The Panasonic GH3 camera improves upon the GH2 in many ways. One improvement is that you can record videos at ISO 6400 sensitivity, while the GH2 only went up to ISO 3200.
This is quite useful. Some months ago, I was recording fireworks, and found that even with ISO 3200, I had to set the shutter speed to 1/12s, and record at only 12 frames per second. With the GH3, I could have set ISO 6400, and used 25 frames per second, a very common FPS setting.
I have tested the ISO 6400 setting at a dimly lit concert. I used the Lumix X 12-35mm f/2.8 lens at 35mm f/2.8. The video mode was the 1080p, 50 fps, and I set the shutter speed to the slowest possible, 1/50s. Here is the result:
In this case, I could probably have gotten better results by using 25 fps, allowing for 1/25s shutter speed, and reducing the ISO to 3200. But here I wanted to test the ISO 6400 setting.
Note that the lightning at the concert was very difficult, with a lot of red coloured lights. With better lightning, the video outcome would have been vastly better.
Here is an extracted frame from the video. I used Kdenlive in Linux to edit the video:
The video mode I used is denoted "MOV FHD 50p" in the camera, and gives 1920x1080 image frames at 50fps. On an NTSC camera, the fps would be 60. This mode gives you 50Mbps bitrate, about twice as much as the highest bitrate the Panasonic GH2 could produce.
For the ultimate in image quality per frame, you could choose the "MOV I FHD 25p" mode, which encodes the video as ALL-INTRA, with a bitrate of 72Mbps. Again, on an NTSC camera, this would be 30p, not 25p.
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:
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:
While testing the Panasonic GH3 camera, I took a series of nine identical pictures using the Lumix X 12-35mm f/2.8 lens in the high speed drive mode, with electronic shutter. They all came out fine, except for one single image, which came out without the pincushion in-camera geometric distortion correction. It also has some corrupted parts in the upper part of the image.
Here is one picture which came out ok, and the one out of nine which came out wrong:
I opened the JPEG file in several image processing programs to verify that the mistake was in the file, not in the editing client.
The RAW image file still came out fine, so this is not a big issue. I wouldn't recommend to avoid the camera because of this finding. It is probably normal that new cameras need some firmware upgrade to behave better. My camera has the original 1.0 firmware.
I later tried to take another long series of images, and they all came out just fine.
To verify that the corrupted image indeed has pincushion distortion, I have superimposed the edges from the JPEG image (in red) on the edges from the RAW image (in blue):
We see that the JPEG image has pincushion distortion, while the image based on the RAW file has the correct rectilinear appearance. If the camera worked well, both images should have the same geometric properties.
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.
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.
Prime lenses are lenses without a zoom function. They have a constant focal length, and a constant angle of view. When the Micro Four Thirds system was introduced, the very first prime lenses were the Olympus 17mm f/2.8 and the Lumix G 20mm f/1.7. While the Olympus prime lens was generally disliked for the limited maximum aperture, the Lumix lens was an instant classic with the brighter aperture and the perceived very good optical qualities.
Since that time, a lot of prime lenses for the M4/3 system have been introduced. In this article, I present an overview of these lenses.
First, here is an illustration which presents the lenses in terms of the focal length (the X axis) and the aperture (the Y axis). In the picture, the lenses are plotted as dots, where the size illustrate their relative price, and the colour the brand:
In the rest of the article, I illustrate what the focal length and aperture means, before going into details about the individual lenses.
When taking pictures, we normally want the resulting image to accurately depict the reality. However, there are times when we rather want to depict a scene in a way that is not consistent with the reality as we see it.
This may sound strange. As the camera industry has spent an enormous effort to realistically depict the scene, why would we want to distort it?
However, keep in mind that one of the current crazes within popular photography is instagram, hipstamatic, and so on, which is all about distorting the images, and making them look unnatural.
Another way in which photos can be distorted is selective focus. The combination of a large sensor and a large aperture can give you an out of focus background when taking a portrait photo, for example. The rendering of out of focus regions is called bokeh, and the effect can be much more pronounced than what you would see with your own eye. Hence, one could argue that this is a distortion of the reality.
Another type of distortion is of course to use a lens with an unrealistic projection, for example a fisheye lens.
In this article, I am looking at another type of distortion: To use an IR filter to keep off the visible light, and hence, to photograph light outside of the visible spectrum.
A number of different types of IR filters are available. Usually, they are categorized by the cut-off frequency. Visible light roughly goes from 340nm to 740nm, with ultra violet (UV) to the left of the visible spectrum, and infrared (IR) to the right, see the illustration below.
The idea of the IR filter is to remove light which is to the left of the cut-off frequency, only leaving the infrared parts of the spectrum.
I tried two filters, both where bought online at a low price:
The filter to the left is labelled with "IR950", meaning that it cuts off all light to the left of 950nm. Hence, it blocks all visible light completely, and even some of the infrared light. The filter to the right is less extreme, labelled "IR680": It retains some visible red light, but cuts off the larger part of the visible spectrum. I start with the one rated the lowest:
IR680
This filter looks completely black, however, when holding it up towards the sun, you can see that it lets some red light through:
To see how it affects the images, I have taken the same image without and with the filter. Here they are:
Without filter, GH2 with Lumix 20mm f/1.7, ISO 160, f/5, 1/160s:
With IR680 filter, GH2 with Lumix 20mm f/1.7, ISO 160, f/2, 1/2.5s:
Based on the exposure settings, we see that the IR680 filter steals about eight stops of exposure, which is a lot. Normally, you need to use a tripod and a slow shutter speed when using an IR filter.
So how is this interesting? It is just a very red tinted photography. However, when opening the RAW image, one can adjust the white balance, which gives a result like this, leaving some false colours:
Another possibility is to desaturate the images, to create black/white photos. Here are the two images desaturated:
Without filter
With IR680
The desaturated images are not that different.
Here is another example image, taken with the IR680 filter, and no desaturation in post processing:
IR950
This filter looks even blacker than the IR680 filter. When holding it towards the sun, it still looks completely black. I tried it on the GF3, GH1 and GH2 cameras, and they could all just see black when using the filter. So my conclusion is that this filter is too extreme to be used with most digital cameras.
Different sensors can have different types of filters in front of the photosites, and hence, react differently to infrared light. That is why I tested three cameras before giving up. It is well known that some cameras are better than others for infrared photography.
I also tested two different lenses, as I have heard that the coating on some lenses can block infrared light.
IR850
I also tried a third IR filter, with a cut-off frequency of 850nm, not pictured above. This filter looks completely black to the human eye, but the camera can see a little bit through it.
I tested it with the Lumix G 14mm f/2.5 lens. Here are pictures of the same scene without and with the filter:
Without filter, ISO 160, 1/4000s, f/2.5
With IR850, ISO 1250, 1/3.2s, f/2.5
The IR850 filter appears to remove too much light for the Panasonic GH2 camera sensor, and is not very useful.
Note that there is a lot of flare in the image taken with the filter. This is not due to the infrared light, but rather due to the strong light source in the centre of the image, and the poor quality of the filter glass. I have written about this effect of using filters here.
Conclusion
I think the IR680 filter lets through too much visible light, and hence, it doesn't create that special effects. On the other hand, the IR950 filter is too extreme. It removes all the light that the camera can see, and hence, is useless.
I would guess that something in between would give more interesting results. Perhaps a filter with a cut-off at around 720nm would be better. Such a filter removes virtually all visible light, and allows you to photograph a band of infrared light, given that the camera sensor is sensitive enough in this spectral range.
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.
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.
Traditionally, lens focus mechanisms have been rather simple, just a cam which pushes the lens elements back and forth as the focus ring turns. Moving the lens assembly away from the film/sensor gives you a shorter focus distance.
In the Micro Four Thirds family of lenses, this mechanism is rather unusual. Only the two first pancake prime lenses, the Olympus 17mm f/2.8 and the Lumix G 20mm f/1.7 feature this type of mechanism, in which all the lens elements move during focus.
Most other lenses feature internal focus, meaning that only one or some of the lens elements inside the assembly move during focus. This has many advantages: It is usually more quiet, the lens can be more solid since there are no moving elements on the outside, and it is usually less noisy.
On the negative side, this type of focus mechanism can give you a change of effective focal length as the focus moves. This is not much of a problem for still photography, but if you are focusing during video recording, it can lead to what is called "focus breathing", as the image zooms in and out a bit as the focus jogs back and forth.
