TTL flash delay

Flash metering has come a long way the recent decades. TTL flash metering for SLR cameras was first introduced by Olympus in the mid 1970's. TTL refers to Through The Lens. The camera measures the amount of light coming onto the film through the lens during the exposure, and cuts off the flash as the exposure is sufficient.

Film based SLR cameras

For film based SLR cameras, this is usually implemented by having a flash light meter in front of the film plane. The amount of light reflected off the film from the flash is metered, and the flash is turned off when there has been a sufficient amount of light for the desired exposure. See the illustration below.

Film based SLR camera with lens

In this illustration, the mirror is raised for exposing the film.

This generally worked well, at least as long as the subject was not too dark or too light, in which case you needed to manually adjust the flash exposure.

Digital SLR cameras (DSLR)

With digital cameras, this does not work well, since the imaging sensor, replacing the film, is not reflective enough. To overcome this problem, most DSLR cameras fire a pre-flash before raising the mirror, and then fire the main flash after raising the sensor and opening the shutter.

The pre-flash is used to determine the amount of flash needed for the exposure. With this method, the TTL flash meter is no longer needed, the camera's ordinary light meter is used. See the illustration.

DLR camera with lens

There are some DSLRs that still measure the amount of light reflected off the sensor chip, and avoid the pre-flash. The Fujifilm S1 and S3 does this.

Mirrorless cameras

As you know, Micro Four Thirds is a mirrorless camera system. So there is no mirror, and no viewfinder prism. The camera also has no light sensor anymore. The imaging sensor is the light sensor.

To find the correct flash exposure, a pre-flash is triggered while the sensor is exposed. Then the camera must make the sensor ready for a second exposure, and fire off the flash with the correct amount of light. This typically takes a bit more time than with a DSLR. The DSLR used the separate light meter for the pre-flash, and could expose the main imaging sensor only once.

Here's a basic illustration of a mirrorless camera with lens. It is much simpler, since there is no mirror, pentaprism, or light meter.

Mirrorless camera with lens

Flash and pre-flash timings

To examine the pre-flash and main flash timings, I have video recorded the cameras using a Panasonic GH1. The recording was done at 50fps (to get the most detailed timing measurement), and at 1/50s exposure, so that I would not miss the flash firing.

Using this setup, I video recorded four cameras doing the flash exposure: The Panasonic GH2 and GH3, Pentax K10D, and the Canon EOS 400D. For all the cameras, I used manual focus when taking the test exposures, so that there would be no autofocus delay. I also set the maximum aperture, to avoid the delay of the camera stopping down the aperture.

During normal indoor lightning

Here are the tests, as recorded by the Panasonic GH1:



And the results:

	K10D	GH2	GH3
Pre-flash delay	460 ms	120 ms	80 ms
Main flash delay	580 ms	220 ms	180 ms

Here, we see clearly that the GH3 improves upon the GH2, however, the results are still fairly similar. The GH3 achieves quicker flash activation, which I believe is because it has a shutter that operates faster. The GH3 also takes more pictures per second during continuous drive mode, another indication that the shutter operation is faster.

During very dim indoor lightning

Here are the tests:



And the results:

	400D	GH2	GH3
1st pre-flash delay	340 ms	120 ms	60 ms
2nd pre-flash delay	none	none	160 ms
Main flash delay	400 ms	220 ms	260 ms

The Canon EOS 400D was the slowest, taking 0.4 seconds from the shutter was pressed, until the main flash exposed the image. The GH2 was the fastest here, however, that was just because the GH3 decided to do two pre-flashes. This was probably done for better flash exposure accuracy. I would guess that it normally uses only one single pre-flash, in which case it would have been the fastest in the test.

Avoiding the pre-flash

The pre-flash can concievably be a problem. It can cause your subject to blink, for example. As long as you use TTL flash metering, be it with the on-board flash or with an original external flash, there is no way to avoid this.

However, if you have an external flash, it is very likely that you can overcome this by using the so-called "auto" mode. Auto mode for a flash means that the flash has a light sensor, which measures how much light is reflected off the subject, and shuts of the flash when there is sufficient. So only one single flash is needed.

To be able to do this, you need to tell the flash what aperture and ISO rating you are using. See this article for some examples of how to do this using older, legacy flash units. If, on the other hand, you have an original flash for the Four Thirds or Micro Four Thirds format, then the flash will read the aperture and ISO settings off the camera automatically. See my review of the Panasonic FL360 for an example.

The downside of this method, is if your subject is unusually light or dark. The flash has no way of knowing this, and will give you a wrongly exposed image. If you see the image come out too bright, for example, adjust the aperture rating (on the flash) up to a larger aperture (smaller f-number).

Conclusion

The GH3 has an impressively fast response here, only 0.06s delay from pressing the shutter until the camera fires the first pre-flash, twice as fast as the GH2. And the total delay is around 0.2s. On top of this, you will mostly add the autofocus delay. However, since you have most likely focused during composition anyway, this is just a matter of the camera confirming that the focus is ok. Using a lens with a fast AF motor, this will take a very short time, probably around 0.1s

In the second test, the GH3 did a second pre-flash, probably at a different exposure level than the first. This was done to probe how to best illuminate the subject. As a subject, I had a wall with very little contrast, so a normal subject will probably not require a second pre-flash.

When talking about cameras like this, most enthusiasts would say that you should not use the built in flash at all. The reason is that it is fairly low powered, meaning that you cannot expose people at a long distance when taking pictures indoor. Any distance larger than about two meters might be problematic, depending on the lens you use, of course, the larger aperture the better. Also, the flash is located quite close to the lens, which gives you a quite flat lightning

However, my experience when using the Panasonic GH3, is that it does a good job when photographing people indoor using the flash, both for portrait closeups (less than one meter distance) and groups of people. Of course, using a proper flash, like the Panasonic FL360, or the more recent predecessor Panasonic FL360L will give you much better flash images. But when you travel light and happen to need the built-in flash, don't be afraid to use it.

Autofocus during video comparison, GH2 vs GH3

When the Panasonic GH1 was announced in April 2009, it had a unique selling point: It was the first and only consumer system camera which could autofocus continuously while recording videos. Since this time, the competition has improved a lot, of course, and all mirrorless system cameras can autofocus while recording videos. But they use different technologies, and the performance varies.

The Panasonic GH3 was released with a claim to have the best AF performance of mirrorless cameras ever, as usual for a new premium mirrorless camera. And the AF performance for single still images is very impressive indeed. However, this doesn't really matter. All current Micro Four Thirds camera focus more than fast enough for static still images. Except possibly with the Lumix G 20mm f/1.7 pancake lens, due to its combination of a fast aperture and an old school focus construction.

What's still a challenge, though, is continuous autofocus during video recording, and focus tracking of moving subjects, in AF-C mode.

The Sony SLT cameras solve this by using a fixed translucent mirror, which means being able to use phase difference autofocus (PDAF) also during video recording. This system is able to track moving subjects very well during video, due to the genuine SLR PDAF technology. However, the cameras are not mirrorless, being DSLR systems with fixed mirrors, which means having larger camera bodies, and, usually, larger lenses as well.

The Nikon 1 system and Canon EOS M system solve this by having on-chip PDAF sensors, directly on the imaging sensor. With this technology, they can combine PDAF and CDAF, however, the real world benefits of this system are still undecided.

Panasonic and Olympus have so far used pure CDAF, with no specialized hardware to aid the focusing. They rather rely on image processing to speed up the autofocus. With the Panasonic GH3 being the most recent premium model, let's see if it actually does improve upon the predecessor GH2. To test the cameras head to head, I mounted both on a plank using Manfrotto Superclamps:



On both cameras, I used the Lumix G 14mm f/2.5 pancake lens. The lens focuses very quickly. Even with the same lenses, the GH2 has a slightly wider field of view in video mode, due to the multi aspect sensor feature, which the GH3 misses.

Here are the results in terms of autofocus performance during video recording:



As we see, the Panasonic GH3 performs much better than the GH2 in term of autofocus. Even with the same basic technology, the GH3 has a better image processing capability, which enables it to focus better while recording videos.

Notice that the GH2 needs to jog the focus back and forth to confirm the focus and settle. This is a typical sign of CDAF focus technology. The GH3, on the other hand, appears to nail the focus straight away, as if it was using PDAF. Which it doesn't.

I think it looks like the GH3 is a revolution when it comes to continuous AF during video for Micro Four Thirds. It may be the first camera to make AF during video truly possible.

And this does work well in real life situations. Here, I have recorded a concert using the Olympus 45mm f/1.8 at f/2, ISO 3200. The light was very dim, around EV2. The autofocus was left on during the video, and it generally keeps the image well in focus. In my experience, the GH2 would not have handled such a situation well:



Keep in mind that AF-C while photographing moving subjects is a totally different subject. I would expect the Panasonic GH3 to perform better here as well, as it is capable of AF sampling at up to 240fps with the most recent lenses, the Lumix X 12-35mm f/2.8 and Lumix X 35-100mm f/2.8. However, I have not tested this feature yet.

High ISO performance of the GH series cameras

When new camera generations get launched, everybody expect the high ISO image quality to improve over the previous generations. While we would use a low ISO as possible at all times some years ago, it is generally quite safe to use ISO 800 with newer generation cameras. Let's take a look at how the Panasonic GH series handles high ISO.

To test this feature, I rigged the Panasonic GH1, GH2 and GH3 on a tripod, using the Sigma 30mm f/2.8. I left the lens wide open, it tends to be quite sharp. To be able to compare the cameras, I set both in the Shutter speed priority mode (S), at 1/10s and auto-ISO. The camera would then select the ISO needed for the exposure to be sufficient. I used Auto White Balance (AWB).

Here are the three images:

GH1, 1/10s, ISO 1250

GH2, 1/10s, ISO 1600

GH3, 1/10s, ISO 1600

These are the out of camera JPEG images, with standard image settings. The histogram below shows that all cameras expose the scene pretty similarly. The GH3 exposes it a bit brighter, though:



Another thing to note is that the GH1 uses the lowest ISO value of the three, 1250. This confirms again that the Panasonic GH1 had a somewhat conservative ISO scale, compared with other Micro Four Thirds cameras.

Looking at the image quality, we can compare 100% crops from all three images. I rescaled the GH1 image, to make it comparable with the 16MP output of the other cameras.



I think we can see that the GH2 images look sharper, but at the expense of shadow details. The GH3 appears to give a higher dynamic range, with more usable details in the dark parts of the image. With the advances of high ISO image quality, I feel quite confident using ISO values of 1600, and even 3200 when needed, with the Panasonic GH3.

GH2 vs GH3 video quality comparison

When Panasonic released the GH3, it was expected to raise the bar even further in terms of video quality. To compare it against the GH2, I connected both cameras to a piece of wood, using Manfrotto Superclamps, so that they would record the same scenery for comparison.



On both cameras, I used the Lumix G 14mm f/2.5 pancake lens, a favourite of mine. I focused on "infinity", and then set both cameras to manual focus. The lenses were set to f/5.6 for the best sharpness, and I used the base ISO on both cameras. With the ambient lighting, the shutter speed was usually around 1/120s. Both cameras had the same settings in terms of sharpening and saturation. It was all recorded in 1080p, 25fps.

Even if the cameras have identical lenses mounted, they still have different field of view during video recording. This is due to only the GH2 having the an over-sized, multi aspect sensor, giving a wider field of view in video mode.

Here are the videos combined, for easy comparison:



Some may doubt that the quality of the YouTube rendering of the video is sufficient to really tell the difference between the cameras. I agree with that, and to assist in comparison, I uploaded parts of the video at 200% size, which probably makes the video image quality easier to assess. And I made some 100% crops from the original out of camera video files, uncompressed in PNG format below:





This last image comparison is from the ISO 1600 footage:

Conclusion

Just like I have concluded previously, the GH3 features somewhat less rolling shutter artefacts in video mode. Further, I think it looks like the GH3 handles high contrast better, and the overall sharpness of the video stream is better. Not unexpected, since the GH3 can record at up to 72Mbps bitrate, as compared with 24Mbps for the GH2. I used 50Mbps with the GH3 here, though. Of course, the bitrate is not everything, the sensor, AA filter, downsampling algorihm and compression algorithm are also important.

I also like the colours of the GH3 better. At high ISO, the GH3 does provide more details.

As far as I can see, the GH3 does deliver on the promise of delivering even better video quality than the predecessor GH2.

AF during video, comparison GH2 vs GH3

Recent Micro Four Thirds cameras have very good autofocus performance for still images. Mostly, the performance is among the best in this class, certainly better than DSLR cameras in live view mode. However, there is one area where mirrorless cameras don't perform well at the moment, and that is continuous autofocus: Both during video recording, and for photographing moving objects, e.g., for photographing sports and birds.

Some camera manufacturers have been trying to solve this by adding phase difference sensors (PDAF) on the imaging chip, like the Nikon 1 and Canon EOS M cameras. However, the real world benefit of that solution is still undecided.

Panasonic have said in interviews that the on-sensor PDAF solution is not going to be used for Micro Four Thirds, at least not anytime soon. Rather, Panasonic expects to achieve better continuous autofocus performance by using faster image readout from the chip, better image processing algorithms, and more processing power. Have they achieved this with the most recent Panasonic GH3?

To compare the autofocus performance during video recording with the GH2, I used a Lego Technic contraption to move a cardboard box back and forth at a steady pace. I then set up both cameras, in turn, with the Lumix X 12-35mm f/2.8 lens at 35mm f/2.8 at close range, and recorded video at 1920x1080, progressive, 25fps. Comparing the resulting footage, it is easy to see which camera better finds the focus during the movement. Here is the video footage, for comparison:



It's easy to see that the GH3 achieves correct focus more often than the GH2, in fact, about twice as often, according to my frame counting. The GH3 also has a better overall sharpness: It is possible to see the offset printing pattern more easily with the GH3. This could be partially due to the multi aspect sensor feature that the GH3 misses: It means that you get slightly narrower field of view when using the GH3, as compared with the GH2, and hence, more enlargement of the subject.

One of the new features of the GH3 is the 240fps contrast detection autofocus (CDAF) sensor readout. The GH2 only does 120fps, maximum. The smaller print in the GH3 specifications state that the 240fps is only possible when using the newest f/2.8 zoom lenses, the Lumix X 12-35mm f/2.8 and the Lumix X 35mm-100 f/2.8.

And can the camera use the 240fps feature during video recording? Probably not, since the sensor is busy reading the image at 25fps for the video stream anyway. I previously compared the GH2 video AF performance during 25fps and 50fps video, and found that it does better at 50fps, indicating that more frequent image readout is better for the AF performance. As long as the shutter speed is faster than the video rate, there is surplus time between the frames for CDAF readout. Perhaps the GH3 camera can utilize this for better AF performance?

Conclusion

The Panasonic GH3 camera appears to be able to focus better during video recording than the GH2, even at the same frames per second (fps) rate.

ETC comparison, GH2 vs GH3

I recently looked at the video quality when using the ETC function, as opposed to using non-cropped video on the Panasonic GH3. My conclusion was, perhaps not surprisingly, that the ETC function adds quite a bit of noise at higher ISO. So while the ETC function is very good to have for extending the reach of your lenses during video mode, you should avoid using it at high ISO unless you really have to.

But what about comparing the GH3 with the predecessor GH2. Both cameras feature the ETC mode. To test this, I set up both cameras to video record the same scene, and used the Lumix G 100-300mm f/4-5.6 lens at 100mm f/5.6. I already know that this lens is very sharp at 100mm, especially when stopped down to f/5.6.

Here is a comparison of the videos outputs:



Also, here are some 100% crops from the video streams:



I think that the cameras perform quite similarly, in this case. I'm actually thinking that the GH2 videos look better in terms of sharpness and noise at ISO 3200. The GH3 has better colours, though.

Of course, the GH3 goes all the way up to ISO 6400 for video, also for ETC, which is an advantage over the GH2 anyway.

One can also argue whether ISO 200 is the same with both cameras. Do the cameras have the same sensitivity at ISO 200, and at higher ISOs? I don't think the jury is fully out on this yet. To try to assess this, I tried to take images at ISO 200 with the cameras GH1, GH2 and GH3. However, even after seeing the results, I am not sure how to interpret them.

Conclusion

The ETC mode is very useful, but avoid using it at high ISO, where it adds quite a bit of noise. The GH2 and GH3 appear to be quite similar in this respect.

Using the Lumix G 100-300mm f/4-5.6 at 300mm in combination with the ETC mode gives an effective reach of around 1500mm equivalent, filling the moon into almost the entire video frame:

One picture, different times

I had the possibility to photograph a nice view early in the morning, and took two images spaced by 29 minutes, to see the difference. I used the Panasonic GH2, since my GH3 is still in for a warranty repair. I did not have a tripod, and handheld the camera with the Olympus 45mm f/1.8 lens.

The first picture was taken at 7:41 in the morning, 35 minutes before sunrise, at ISO 1600, f/2, 1/25s:

The second was taken at 8:10 in the morning, six minutes before sunrise, at ISO 160, f/2.5, 1/45s:

In practice, I took a series of four images in both cases, and then later chose the least blurry of them. That's how I handled the slow shutter speeds without a tripod.

I think most would agree that the first image is the most striking, at least at first glance. It has the deep blue tint associated with the early morning, and there is the contrast with the yellowish artificial lights.

To be able to photograph the first one without a tripod, I needed to push the ISO rather high, at ISO 1600. This is at the border of what the GH2 can handle, and the image quality suffers. Here is a comparison at pixel level between the images shot at ISO 1600 and ISO 160:

Note, though, that this difference is not purely due to ISO differences. The first image also has a slower shutter speed (1/25s versus 1/45s) and a larger aperture (f/2 versus f/2.5), both potentially making the image less sharp. The Olympus 45mm f/1.8 lens is quite sharp, but you'll usually notice that the sharpness increases quite a bit when stopping down from f/1.8 to, say, f/2.8. Despite this, I think the first image could well be printed fairly large without any problems.

The pictures above are from the out of camera (OOC) JPEGs. One could say that the first of the images is rather blue. However, this is not the GH2 auto white balance doing anything wrong, it was quite simply very blue this early in the morning. Opening the RAW image in Lightroom 4, it could be edited to something like this:

I think this edited version is probably a bit more striking.

Conclusion

After having looked at these images, I think it is quite impressive that it is possible to take a handheld image half an hour before sunrise, and even with a tele lens to boot. This shows how far the technological development has come.

Still, the image quality could be improved by using a tripod. If I had a tripod, I could have set the shutter speed to, e.g., 1 second, and used a significantly lower ISO, and a larger aperture for the best image quality.

Sigma 19mm autofocus comparison

The Sigma 19mm f/2.8 EX DN is perhaps a strange lens. In terms of specifications, it is quite close to the Lumix G 20mm f/1.7 pancake lens, except that it is slower, and less compact. So, why would anyone be interested in it?

Lately, it sells at a reasonable price, and besides, it features the normal internal focus system, while the Lumix G 20mm has an old style focus mechanism which moves all the lens elements, being slow and noisy.

I have found that the Sigma 19mm lens is slightly less sharp than the Lumix 20mm lens, at similar apertures. This is consistent with other people's findings.

With still images

What about the autofocus performance, then? Is it faster, as one could guess? Here is a comparison where I put both lenses on the Panasonic GH2, and focused down to around 0.3m:



The Sigma 19mm lens spends 0.28s focusing down to close to the minimum focus distance, while the Lumix 20mm lens needs 0.64s. So the Sigma lens is indeed faster, as we had expected in advance.

During video recording

Another important aspect is continuous autofocus during video. This is still the achilles' heel of the Micro Four Thirds system, and not even the most recent cameras do this well.

To test it, I mounted the Panasonic GH2 with the Lumix G 20mm f/1.7 lens to a wooden plank, and next to it, mounted the Panasonic GF3 camera with the Sigma 19mm f/2.8 lens. I used Manfrotto Superclamps to mount the cameras, just like when I tested the rolling shutter properties of the GH2 and GH3. I set both lenses to f/2.8 for similar depth of focus properties.

Of course, the 19mm lens has a wider field of view. But on the other hand, the GH2 has the multi aspect sensor, oversized sensor property, which gives relatively wider field of view in video compared with the non-multi aspect sensor GF3 camera. So the field of view is probably quite similar for the two cameras.

Here are the two video footages, combined to one clip. To see the focus performance, it is best to view this in 1080p, click on the youtube icon to access this possibility.



The results are not completely consistent, but I think the Sigma 19mm lens and GF3 combo keeps the focus better during the video. One could speculate that the GH2 probably has the better image processing technology, and hence, should have the advantage in terms of handling continuous autofocus. Despite the handicap of being combined with the basic GF3, the Sigma lens performs better.

It would have been better to mount the lenses to the same camera, of course, but I don't have two of the same camera model. Also, I would normally have used the newer GH3 camera, but my camera is sent back for repair. I hope I get it back soon, and that I don't have to wait for three months, like I had to when sending back the Lumix G 14-42mm lens for misaligned aperture diaphragm blades.

Conclusion

What this shows, is that the Sigma 19mm f/2.8 EX DN lens is better for video use, as long as you can live with the f/2.8 aperture. While it is not as sharp as the Lumix G 20mm lens, it is still very sharp, and certainly more than sharp enough for video use. The autofocus is also less audible.

Even if the Sigma 19mm lens is larger, it is still quite non-obtrusive, with a matte black finish.

The Lumix G 20mm f/1.7 pancake lens is a classic Micro Four Thirds lens, praised for the very good sharpness. However, people also find it annoying for the slow and noisy autofocus performance. People have also reported that the focus mechanism can be clogged with dust, due to the moving front elements. The Sigma lens has no moving lens elements on the outside (only internally), and is probably more solid in that way.

Given the low price the Sigma 19mm f/2.8 EX DN sells at, it can be considered a good value for money, and an interesting alternative to the Lumix G 20mm f/1.7.

I haven't tested the "brother" lens, the Sigma 30mm f/2.8 EX DN in the same way, but I would guess that it, too, performs well in terms of autofocus speed.

GH2 vs GH3 rolling shutter evaluation

The Panasonic GH1 and GH2 had pretty much the same rolling shutter properties. I have previously examined the rolling shutter artefacts of the GH3, compared with the GH2, and found that the GH3 has somewhat less artefacts. But my test was based on a rotating propeller setup, which is not so realistic.

Rolling shutter artefacts are typically identified when panning quickly during video recording. This can lead to "wobbly" effects, square objects can be seen to lean towards one side.

To compare these artefacts again between the GH2 and GH3, I mounted both cameras to a piece of wood:

I used Manfrotto Superclamps with ball heads to fix the cameras to the piece of wood. These are quite useful.

GH2 vs GH3, AF speed comparison

All new premium Micro Four Thirds cameras come with a claim to have the fastest AF ever, and this applies to the Panasonic GH3 as well. The GH2 improved upon the GH1 by adding 120fps AF readout from the sensor (in bright light), and the GH3 ups this to 240fps. However, this feature is only available with the Lumix X 12-35mm f/2.8 and 35-100mm f/2.8 zoom lenses, and then only with the most recent firmwares. Probably, this only works in bright light, otherwise, one would guess that the camera chooses a slower sample rate.

I've tried to measure the focus speed of the GH3, compared with the GH2. I did so in two lightning conditions, moderate indoor light (6 EV), and very low indoor light (3 EV). I also used two lenses, the Sigma 30mm f/2.8 EX DN and the GH3 kit lens Lumix X 12-35mm f/2.8.

I tested them by setting the cameras on a tripod, with centre spot focus mode enabled. And I put a small figure on the table in front of the cameras, with a distance of about 40cm. When turning on the camera, the lenses are usually reset to around infinity focus.

I video recorded the process using a GH1 camera. To measure the time the camera needs to focus on the figure and take the picture, I've analysed the audio, to find the time from my finger taps the shutter button, until the camera snaps the picture.

Here are some example tests in moderate light (6 EV):



And the results are:

Lens / Camera	GH3 (6 EV)	GH3 (3 EV)	GH2 (6 EV)	GH2 (3 EV)
Sigma 30mm	0.54s	0.63s	0.61s	0.52s
Lumix X 12-35mm @ 35mm	0.23s	0.74s	0.43s	0.45s
Lumix X 12-35mm @ 12mm	0.18s	0.25s	0.27s	0.28s

In the table, we can note that in the GH3 excels in good light with the Lumix X 12-35mm zoom lens, especially in the wide setting. This is as expected: The GH3 can use the higher framerate for the AF sensor output in bright light.

In dim light, though, the results are a bit unexpected: The GH2 comes out the best. This may be down to the fact that the GH2 is more mature, the firmware has been updated some times for better AF performance. I guess the GH3 will too, and probably the AF performance will be tweaked for the better in the future.

There is also the odd result that the GH2 and Sigma 30mm combination performs better in very low light than moderate light. I would attribute this to some random variations. After all, these are just single observations.

Conclusion

The GH3 performs very well in reasonable light, especially with the Lumix X 12-35mm f/2.8 kit zoom lens. However, in very dim light, it is not as good as the GH2. However, keep in mind that the GH2 has a more mature firmware.

GH1, GH2 and GH3 @ ISO 200

Whenever a new camera is launched, there is usually a lot of discussions about what the true ISO values of the camera is. Is the ISO rating conservative, meaning that the true sensitivity of the camera is higher than the rated sensitivity? Or are the manufacturer cheating by stating that the sensitivity is ISO 200, for example, when in fact it is ISO 100?

To try to shed some light on this question regarding the Panasonic GH series, I have taken a picture of the same scene at the same time of day with the three cameras. I used the same lens, the Lumix G 20mm f/1.7, and I set the aperture to f/1.7. The other settings were: ISO 200, 1/250s, sunny white balance. Here are the out of camera JPEGs:

GH1:

GH2:

GH3:

When isolating only the wall part of the image, and looking at the histograms, it reveals that the ISO ratings are probably a tad bit different:

This indicates that at ISO 200, the Panasonic GH1 appears to be a bit more sensitive, while the GH2 and GH3 appear to be fairly comparable. This is consistent with the DXO ratings, which show the GH1 to be more sensitive than the GH2.

Note that the above results are based on the out of camera JPEG images. I have also developed the RAW images using Lightroom 4.3 RC with no exposure compensation, and gotten these histograms:

These results indicate a similar conclusion as the JPEG tests: The GH1 has the higher sensitivity at ISO 200, while the GH2 and GH3 are fairly similar.

Using the RawDigger program, I extracted the average exposure from the wall area of the images, again from the RAW images. The results are here:

Camera	GH1	GH2	GH3	GH3(*)
Red	215	153	267	123
Green	618	427	470	326
Blue	430	287	346	202
Green2	612	422	471	327

The current version of RawDigger does not set any default black level offset for the GH3, since it is a new camera. For the GH1 and GH2, it sets a black level offset of 15. Some say that the Panasonic GH3 should have a black level offset of 144, in which case you get the rightmost values in the table, denoted by "GH3(*)". The other GH3 column is taken without any black level offset.

For comparison, here are the images converted from the RAW files using Lightroom:

GH1:

GH2:

GH3:

GH3 has less rolling shutter artefacts than GH2!

Rolling shutter denotes a type of shutter mechanism, and can refer to both a mechanical shutter, and an electronic shutter. It also refers to the type of tilting artefacts you get when panning quickly during video recording. Some refer to these artefacts as "jello video".

This is not strictly related only to digital cameras. Older film based cameras often feature a focal plane curtain shutter, which "rolls" across the film plane and exposes the film horizontally or vertically. A very famous example of this is the racing car picture taken in 1913 by Jacques Henri Lartigue using a 4x5 Speed Graphic camera.



The shutter moves relatively slowly on this camera, when compared with modern SLRs, which gives the distortion of the racing car. The distortion is especially visible in the wheels, which appear to be leaning forward. This effect was later copied by cartoonists when they wanted to give the impression of speed.

Fisheye sharpness

When I reviewed the Samyang 7.5mm f/3.5 fisheye, it was natural to compare it against the native Lumix G 8mm f/3.5 fisheye lens. Since the Lumix lens costs about 2-3 times the price of the Samyang lens, I would expect that the Lumix lens comes out as the winner.

However, what I found was that the Samyang lens was sharper, even in the extreme corners, and without the in camera CA correction which is done with the Lumix lens when using it on a Panasonic camera.

Some have doubted this result, and I have also been a bit unsure now and then. So I decided to do another test.

This time, I photographed a couple of trees against the bright sky, a useful test for lens sharpness. The focus was set on the centre of the image. With the Lumix lens, I used autofocus, and set a centre spot. With the Samyang lens, I used the 10x focus assist magnification available with the Panasonic GH2 camera. Here are the two images, both at f/3.5:

Samyang 7.5mm f/3.5	Lumix G 8mm f/3.5

To better evaluate the sharpness performance, I have compiled some 100% crops. From the centre of the image:

And from the top right corner:

Based on this study, it is perhaps not correct to say that the Samyang lens is much better. I think the Samyang lens appears to have slightly better sharpness in the corner, but the differences are fairly subtle.

Keep in mind that the Lumix lensis automatically corrected for CA artifacts, though. By looking at the RAW image files, and converting them to JPEG with third party software, we can see how the images were before the software CA corrections. These 100% crops are from the top left corner:

I used the free program UFRaw to convert the RAW images, but any program could have been used here, as long as it allows for doing the conversion without applying CA correction.

Here we see that without the in camera software CA correction, there are some significant red/green fringing artifacts. These are largely removed in the out of camera JPEG image. In the light of this, the Samyang lens's performance is even more impressive, as no in camera CA correction was done.

Conclusion

I wouldn't say that the Samyang 7.5mm f/3.5 fisheye lens is significantly better than the Lumix G 8mm f/3.5 fisheye lens, even if it appears to perform better in this test. So the image quality should not be an important factor when deciding between the two.

You could also consider the fact that they have slightly different projections. The Samyang lens gives images that are slightly less barrel distorted, and may be easier to defish.

The Samyang lens also handles flare better, see a direct comparison between the two in my review. Flare handling is very important for a fisheye lens, since you are quite likely to find the sun or a strong light source inside the image frame, due to the wide field of view.

When focusing manually with the Samyang lens, it is important to keep in mind that you shouldn't blindly trust the focus distance scale. On my lens, it is slightly off, and I reach infinity focus slightly before the infinity mark. This is not uncommon with manual focus lenses. Exact calibration would be very expensive, and the producers usually leave some slack for themselves by allowing the lens to focus beyond infinity.

The autofocus of the Lumix G 8mm f/3.5 fisheye isn't really needed for landscape pictures, as you easily get infinity into focus manually. But when taking closeup images, the autofocus can come rather handy.

Continuous AF during video with the GH2

The Micro Four Thirds mirrorless cameras use a totally different autofocus method than traditional SLR and DSLR cameras. The M4/3 cameras use a technique called Contrast Detection Autofocus (CDAF), whereas SLR systems typically use Phase Detection Autofocus (PDAF), also called Phase Difference Autofocus.

CDAF relies on jogging the autofocus back and forth to find the setting with the most contrast, in which case the camera assumes the image is in focus. For still images, this works very well. My study shows that both the GH1 and GH2 feature very fast autofocus, especially with the kit zoom lenses. I don't think that SLR cameras can do this much faster, at least not faster in a noticeable way.

The GH2 can sample the contrast 120 times per second (120fps), which allows for a faster autofocus, given that the lens is also capable on reacting fast enough. The GH1 could only sample at 60fps.

The Panasonic GH3, due to be available late 2012, further improves upon this by allowing for 240fps CDAF readout. However, Panasonic says that at the moment, only one lens supports this, the Lumix X 12-35mm f/2.8, and only after firmware update, which was announced today, coincidentally.

Continuous autofocus during video recording, though, is one area where the Micro Four Thirds cameras currently do not perform very well.

One thing to keep in mind, is that when taking still images, the sensor is free to be used for AF before you snap the image. When recording video, though, the sensor is busy scanning your video stream, and cannot be used for high speed CDAF sampling in the same way.

The GH2 can record videos at three different rates: 24fps, 25fps and 50fps (24fps, 30fps and 60fps for American versions). The 24fps, 25fps and 30fps modes are popular for their progressive image stream, and high bit rate. However, keep in mind that in these modes, the camera can only sample the contrast at a low rate, hence, I guess that autofocus during video will also be slower.

The interlaced 1080i mode, 50fps for the European version and 60fps for the American version, can scan the image scene twice as fast, and hence one can guess that the AF is also faster.

The test

I have tried to test this with a controlled case. I rigged up a picture which moves back and forth (using a LEGO Technic mechanism). This is used to test the autofocus performance in both the 50i and 25p modes of the GH2, using three different lenses, the Lumix X 45-175mm f/4-5.6, Lumix G HD 14-140mm f/4-5.8 and Olympus 45mm f/1.8. All of these lenses are marketed as video optimized.

Here is a video showing the test setup, and the outcomes of the tests:



Analysis

By looking at the videos, I think it is quite clear that the focus is kept better when recording at 50fps, compared with 25fps. To be more sure, I looked through the first full cycle when using the Lumix X 45-175mm f/4-5.6. The cycle from the rear position, moving forwards and then backwards again to the same position takes 140 frames, or 5.6 seconds.

At 50fps, I counted 71 frames in focus (51%), while at 25fps, the number of frames in focus was 59 (42%). This is hardly a scientific analysis, but I think it confirms that my theoretical guess also holds in practice: When recording at a higher frames per second rate, the continuous autofocus works better.

Conclusion

When the continuous autofocus performance is important, you could consider video recording at a higher frames per second rate. This gives the camera a better chance of keep up the focus, given that there is sufficient light.

On the other hand, the GH2 camera can only provide the interlaced mode at 50fps/60fps at 1080 lines resolution. The interlaced mode probably gives slightly less perceived sharpness anyway.

Future cameras are expected to provide the progressive mode at 1080 lines resolution (1080p) at 50fps/60fps. With this capability, I would certainly recommend using 1080p at 50fps/60fps when the autofocus performance is crucial, and when there is sufficient light.

Technical improvement potential

One could imagine improvement potential within the technical limitations of the autofocus system. As I have demonstrated in this article, the frames per second rating affects the autofocus effectiveness. As the sensor is used to record the video stream, it cannot at the same time be used for autofocus at a faster rate.

However, it is quite often that you don't use a 360° shutter. A 360° shutter means that the shutter stays open all the time. Hence, at 25fps video recording, the shutter speed is 1/25s. At this fps and shutter speed combination, the sensor is always busy reading the video stream.

However, what if you use a 180° shutter? At 25fps, that would correspond to 1/50s shutter speed. At this rate, there is a 1/50s gap between each frame which could be used for reading out CDAF information, see the illustration below:

Using this method, there is room for one exposure, and two additional CDAF readouts per frame when using a 180° shutter. Perhaps the GH2 uses this technique today, I don't know. These technical details tend to be secrets.

Alternative techniques for AF during video

The Micro Four Thirds cameras so far only use CDAF for autofocus, both for still images, and during video. There are some other techniques out there as well.

The Sony Single-Lens Translucent (SLT) cameras use a permanent (non-flapping) mirror which is semi-transparent. This mirror allows for using traditional SLR style PDAF sensors, meaning that the camera can operate the focus very quickly also during video recording.

This has an additional advantage over CDAF: There is no need to jog the focus back and forth to find the maximum contrast, as the Micro Four Thirds cameras do. Hence, you will see that the cameras do not "overshoot" the focus. When needed, the focus changes to the correct distance at the first attempt, given that there is sufficient light.

The disadvantage of the SLT system is the requirement for a traditional mirror box, making the cameras larger and more complicated, as well as requiring the lenses to be designed for a longer register distance, resulting in larger and heavier lenses.

The Nikon 1 system has an alternative approach. It uses an imaging sensor where some of the photosites are PDAF sensors. This allows for a hybrid CDAF and PDAF system: The camera can choose which system to use depending on the situation. In theory, this is the best of both worlds, as it can keep the register distance short, while allowing for faster autofocus during video recording. I have not tried the Nikon 1 myself, though, so I don't know the real world merits of the system.

According to interviews with designers and engineers, there are no plans to change the autofocus system of the Micro Four Thirds cameras. In theory, it should be possible to improve the CDAF system with better and faster image processing. Hence, we can expect the continuous autofocus to gradually improve with newer cameras.

Air show video using the Lumix 100-300

During the September 1st Royal Norwegian Air Force 100 year anniversary, I tried to video record some of the air plane flybys. This was the very first time I had tried to video record air plane, and I brought the longest lens I have, the Lumix G 100-300mm f/4-5.6 with the Panasonic GH2 camera.

I did not bring any tripod or extra microphone, as I would be standing in a crowd of people, and needed to be fairly agile.

Most of the time, I used the lens in the longest setting, at 300mm, and stopped down the aperture a bit to f/6.3. I could do this at ISO160, the base ISO, and still have a healthy shutter speed of about 1/500s, even when dialing in about +1/3 to 2/3 of exposure compensation. I needed the exposure compensation, as I was mostly shooting into the sun, or close to the sun.

Here I have edited the footage into a video stream of about three minutes with some of the footage:



I used Kdenlive to edit the stream, and I added a bit of post process image stabilization to the video. This was needed, even though I used the OIS feature of the lens. Perhaps I would have been able to go without the extra image stabilization had I used a tripod.

Some things to note about the video:

• There is quite clearly still some vignetting, even though I did stop down an extra 1/3 of an aperture stop.

• You can see the lens OIS working, as the brightest central disc area moves about in the frame.

• The focus is mostly ok. Some times, the camera loses focus for a short period, but it is not a big problem. I had the AF-S mode selected.

• The sound is not very good. An external microphone would probably have improved it.

• You can see the evidence of rolling shutter distortion. Here is a frame from a video, where the helicopter blade is bent due to the rolling video shutter:
  
  
  
  
  When using the mechanical shutter for still images, though, there is virtually no rolling shutter effect:
  
  
  
  
  This is because the mechanical shutter travels faster than the electronic line by line readout of the sensor is.

Fireworks recorded using GH2 and Samyang 7.5mm f/3.5 fisheye

It was very dark during this firework, so to record it, I had to push the exposure as high as possible. I used the "Creative Movie Mode", with the manual setting ("M"), in which I could dial in ISO 3200 (the maximum), and used the largest aperture on the Samyang 7.5mm fisheye lens: f/3.5.



A little known feature of the Panasonic GH1 and GH2 is that you can record videos with a slower shutter speed than the frames per second setting. I was using the high bit rate 25 fps 1080p mode, and to get sufficient exposure, I set the shutter speed to 1/13s, i.e., slower than 1/25s. This is possible only in the "Creative Movie Mode", in the "M" exposure mode, and with autofocus turned off. Of course, you don't actually get 25 frames per second with a shutter speed of 1/13s, you only get 13 frames per second.

To make the video clip more interesting, I speeded up the video to 200% speed, meaning that the frames per second of the output clip was about 25fps.



I also changed the tempo of the sound, to keep it in sync with the 2x fast video.

Conclusion

The Samyang 7.5mm f/3.5 fisheye lens is very good for recording fireworks. But to get sufficient exposure, you may need to set the shutter speed quite low, lower than 1/30s, giving you fewer frames per second than you are used to. This feature of the Panasonic GH1, GH2 and GH3 cameras is quite useful, and I don't think other Micro Four Thirds cameras can record videos with this slow shutter speeds.

When the GH3 gets released soon, I would guess that it can record videos at ISO 6400, which may solve this issue.

2x Fisheye on a bicycle

It so happens that I have both the fisheye lenses available for Micro Four Thirds at this time. I bought the original Lumix G 8mm f/3.5 fisheye when it was available. It is a fine lens, for sure, with good sharpness even in the corners.

The Samyang 7.5mm f/3.5 fisheye lens did interest me, and I decided to pick that one up as well. It is much cheaper, and performs even better optically, in my experience. The Lumix lens can be better when photographing close items, like closer than around 30cm (one foot). Then, autofocus is useful. Otherwise, I generally use the Samyang lens now.

But having both at the same time can also be useful. Since I have both the GH1 and GH2 cameras, I can use both lenses at the same time. Mounting them both to my bicycle using Manfrotto Superclamps and ballheads, I can record the scenery passing by from two angles, which can make some interesting footage:

Here is the footage I ended up with, after editing the video. I'll get back to the details of how I edited it later in this article:



Front camera

Pointing forwards, I have the GH1 camera with the Lumix G 8mm f/3.5 fisheye lens. The camera is set to auto-ISO. With the exposure set to f/3.5, 1/25s, the camera has picked the maximum ISO 1600 for most of the ride, which is still a bit too low, leaving the footage a bit underexposed. I pre-focused at about 1m distance, and left the autofocus off. The camera records at 25fps 1080p.

Rear camera

Pointing backwards, I have the GH2 camera with the Samyang 7.5mm f/3.5 fisheye lens lens. I used the same settings as for the GH1 camera above. However, the auto-ISO goes to 3200 for videos, and hence, the rear camera has a better chance at capturing a more correct exposure.

In my experience, both cameras will consistently underexpose when using the Samyang lens at night, with high contrast. So I dialed in +1 1/3 exposure compensation.

Video editing

First of all, I had to synchronize both video streams, which was quite difficult. In retrospect, I should have clapped my hands in front of both cameras, to have a more clear point of reference.

Here you can see both videos in the Kdenlive video editing software timeline. The GH1 footage is on the top. I'm using the audio from the GH2, pointing backwards.

Then, I wanted to fit both videos into one single frame. This was achieved by cutting off the top and bottom of the original frames, and then compressing the rest by about 20%. To do this, I use the "Scale and Tilt" effect in Kdenlive, with these parameters:

Here is an illustration of an example image frame before and after cropping and scaling:

After halving the vertical size of each stream, I can fit both of them into one 1920x1080 video frame.

Conclusion

One would think that having two lenses that are virtually equal is a waste of money, but it can give you some creative possibility.

After seeing the resulting video, I think I should have cut it much shorter. I doubt that many will want to see the whole thing, as it is too long.