Sunday, 26 August 2012

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.

Sunday, 19 August 2012

Number of aperture blades

Lens specifications are not complete without detailing the number of aperture blades. But what does it mean in practice?

Of course, the shape of the aperture blades is important for the out of focus highlights, the bokeh. I have previously seen that the Lumix 45mm f/2.8 1:1 macro lens has somewhat more rounded aperture when stopped down than the Olympus 45mm f/1.8. When not stopped down, i.e., at the largest aperture, the diaphragm blades move out of the way, and the opening is usually perfectly round.

Adding a higher number of diaphragm blades can make the aperture opening more rounded when stopping down. However, lenses seldom go beyond nine blades, probably for the reasons of cost, complexity, and the risk of having one of them break down.

It turns out that the number of blades is also related to the rendering of flare, strong light sources inside the image frame. I'll look at that later in this article.

Samyang and Lumix fisheye lenses

There are currently two fisheye lenses available for the Micro Four Thirds system, the Samyang 7.5mm f/3.5 and the Lumix G 8mm f/3.5:



Of course, the major difference between these lenses is the price (the Samyang is the cheaper), the image quality (the Samyang is better, in my opinion), and the focus mechanism (only the Lumix lens has autofocus). But in addition: The Samyang has six aperture blades, and the Lumix has seven. These close up pictures show the rear exit pupil at f/5.6 for both lenses. The Lumix G 8mm lens has more rounded aperture blades, but you can still make out seven segments:

Samyang @ f/5.6Lumix @ f/5.6

Here is a video showing how the aperture blades open up on the Samyang lens:



Affecting the flare

It turns out that the number of aperture blades affect the flare in a fundamental way. It is common to get a star shaped flare when using small apertures. And the number of spikes in the star is the number of diaphragm blades (when that number is even), or twice the number of diaphragm blades (when that number is odd). Hence, using the Samyang should give us stars with six spikes, and using the Lumix should give fourteen. Let's check, by taking pictures at f/22:

Samyang @ f/22Lumix @ f/22

To see this more clearly, here are enlargements at f/22 and f/11:



It's not so easy to count the number of spikes on the Lumix image to the right, but I think it is still quite clear that it is fourteen.

Conclusion

To my experience, most lenses have an odd number of aperture diaphragm blades, which produces the most spikes on the star shaped flare around bright objects, e.g., the sun. I guess this is because a larger number makes the flare look more blurred, whereas a small number makes the flare more distracting.

A bit of trivia is that Canon has chosen an even number for most of their lenses, while Nikon is going for an odd number. Hence, it is often easy to guess what brand a photographer uses, based on an image where the sun is inside the frame. However, the aperture also needs to be fairly small to see this effect, e.g., f/16 or f/22.  So you might not be able to make this out based on any picture.

Saturday, 11 August 2012

Use of a fisheye lens

Fisheye lenses have traditionally been exotic, expensive items. Now, however, Samyang has brought out the 7.5mm f/3.5 fisheye lens for Micro Four Thirds at a reasonable price. Also marketed as Bower, Rokinon and Walimex, this lens brings the fisheye possibilities to the masses.


But, what should you use a fisheye lens for, in the first place? One obvious answer is when you want to capture a very wide scene. The so called full frame fisheye lenses have a 180° diagonal field of view, corresponding to 132° horizontally with the 4:3 aspect ratio. This is significantly wider than the Lumix G 7-14mm f/4 at the widest setting, and that is the widest rectilinear lens on Micro Four Thirds, and very expensive to boot.

However, in my opinion, there are other advantages of fisheye lenses as well, one being that you have the possibility to combine near and far objects in the same image frame. I will illustrate this with an example.

With 14mm

I wanted to photograph a memorial tree together with a plaque on the ground. Here is my first attempt using the Lumix X PZ 14-42mm f/3.5-5.6 lens at 14mm f/8, 1/40s:


As you can see, the memorial plaque on the ground, covered with roses, is simply not readable, even if I did print this image at a large size. So I could try to go a bit closer:


Now, one could conceivably read the text on the plaque, with some effort. But even less of the tree itself is visible now. So this is still not a good compromise.

With fisheye

I switch to the Samyang 7.5mm f/3.5 fisheye lens. Here is one attempt. I focus at about 0.5m distance, and set the aperture to f/11 for a good depth of focus:


Now, the text is readable, the whole tree is visible, and as a bonus, the City Hall, the twin tower brick building to the left, is inside the frame!

To get a slight variation, I move the camera closer to the plaque, and angle it more upwards, using the 3:2 aspect ratio. This gives me the text even more readable, with the whole tree inside the frame. With this picture, I lose the roses placed in the shape of a heart, though:


For web use, and when printing small, I would prefer this last shot, where the text can easily be read.

Side effects

There are some negative effects, though. In the fisheye images, the tree now looks very small. This is not due to the fisheye properties of the lens, but due to the wide angle properties. You would get the same effect when using the Lumix G 7-14mm f/4 in a wide setting.

With wide angle lenses, you can go close to a subject, making the perspective look quite unusual. You'll get near objects looking larger than what is expected, and far objects looking smaller. This is the reason why portrait lenses tend to be long, to avoid these wide angle effects. Taking wide angle portraits of people makes them look "horsey", with large chins and noses.

Another side effect is the fisheye property, of course, making straight lines not passing through the centre of the frame look bent. If you dislike these effects, you have the possibility of defishing the image.

The result can look like this:


Read about how to do the defishing here.

The image now looks quite stretched in the corners. This is not really due to the fisheye properties of the lens, but rather due to the extremely wide perspective. If you had a rectilinear lens capable of this wide field of view, it too would give you the stretched look in the corners. Such a wide rectilinear lens does not exist for Micro Four Thirds, though, and will probably never appear, as it would be very expensive to make.

To avoid this stretched look, one could just choose a smaller amount of defishing. One way could be to use the equirectangular lens model, rather than the orthographic lens model. That yields this image:


Since this last image is not truly defished, it has some residual barrel distortion. But it still looks quite natural.

Conclusion

A full frame fisheye lens can be used for much more than just very wide panoramas and cute close up pictures of animal faces. In fact, having a fisheye lens in your lens bag can solve your composition problems in tricky situations, and give you extra creative possibilities.

The Samyang 7.5mm f/3.5 fisheye lens is very sharp, and handles flare well. In my opinion, it is a good alternative to the much more expensive Lumix G 8mm f/3.5 fisheye lens.

The only way in which the Lumix lens is better, is that it gives you autofocus. This is not normally needed for a fisheye lens, but comes in handy if you want to photograph something very close, i.e., closer than about 0.3m (one feet).

The camera also appears to handle the exposure and colours better with the native Lumix lens. With the Samyang lens, the GH2 tends to underexpose, especially in high contrast situations, e.g., night photos. I usually dial in +1 to +1 2/3 exposure compensation at night.

Friday, 3 August 2012

Bokeh comparison

With kit zoom lenses, the bokeh, the rendering of out of focus areas, is not too important. This is because they feature a small maximum aperture, leaving quite a lot in focus anyway. So that the rendering of out of focus objects is less of an issue, with most of the image in focus.

When using prime lenses with a larger maximum aperture, though, the bokeh becomes more important. With a larger aperture, you're more likely to find the background or foreground out of focus, and the quality of this rendering matters.

I've looked a three common prime lenses. The Lumix G 20mm f/1.7, the Sigma 30mm f/2.8, and the Olympus 45mm f/1.8. Out of these three, the Sigma lens is the odd man out, with a not too impressive max aperture of f/2.8. On the other hand, it is also the cheaper of the three lenses.


From my previous experiments, I know that both the 20mm lens and the 45mm lens have quite ok bokeh. The 20mm lens can give out of focus highlights that are elliptically shaped outside the centre of the frame. The 45mm lens is pretty much unproblematic. But the 30mm lens is a bit of an unknown to me at this time.





First test

My first comparison is done in the morning, with a low sun behind some foliage. I focused on the LEGO figure in the centre. I moved closer with shorter lenses, so that the LEGO figure fills out about the same space in the frame. The distance is about 0.9m with the longest lens, and around 0.4m. The distance is slightly shorter than what you would use when photographing the head of a person, given the same lens.

This situation will typically reveal lenses that render the out of focus background in a "busy" way. Ideally, we'd like to see the lenses blur the background so that it does not distract the viewer from the main subject.

Here are the full images, with all three lenses. They are all taken using a tripod, at ISO 160 on a GH2, and the exposures are generally between 1/60s and 1/5s. I used autofocus, and set a small centre spot area. Click for larger images:

Lumix G 20mm f/1.7 Sigma 30mm f/2.8 Olympus 45mm f/1.8

To look at how the centre, which was intended to be in focus, was rendered, here are some 100% crops from the centre area:


And from the top right corner:


Second test

My first comparison is done at night time, with high contrasts. I have focused on the basket of a bicycle, and there are some lights in the background. With the shorter focal length, I moved closer to the basket, so that the framing is pretty much the same. The distance is about what you would use when photographing the head of a person, given the same lens.

Here are the full images, with all three lenses. They are all taken using a tripod, at ISO 160 on a GH2, and the exposures are generally between 1/2s and 4s. I used autofocus, and set a small centre spot area. Click for larger images:

Lumix G 20mm f/1.7 Sigma 30mm f/2.8 Olympus 45mm f/1.8

To look at how the centre, which was intended to be in focus, was rendered, here are some 100% crops from the centre area:


I wouldn't use these to evaluate the sharpness, as I am not 100% sure that the camera focused at the very centre each time.

And a look at the out of focus rendering of the background highlight:


Conclusion

This comparison shows us that the bokeh of all these lenses is quite good. The Lumix G 20mm f/1.7 has elliptical out of focus highlights outside of the centre, as we have seen previously.

On the other hand, both the Sigma 30mm f/2.8 and the Olympus 45mm f/1.8 display slightly "busy" out of focus rendering when wide open. These two lenses could have blurred the background in a more pleasing way, but this is not a big deal. I don't think the background is very distracting in my test.

My perception is also that the Sigma 30mm f/2.8 lens handles high contrast situations the best. It appears to retain the contrast well, and flare/ghosting is not a problem. For a night exposure, I would use this lens when possible. This property may be due to the relatively simple construction of the 30mm lens: It does not have a large maximum aperture, not a wide angle, and is not a pancake. Hence, the optical construction is more trivial.

Another conclusion to be made, is that a longer lens gives more out of focus images, given the same framing and aperture. If you're after this effect in your images, it may pay to look for lenses that are long.




Wednesday, 1 August 2012

Lumix G 12.5mm f/12 3D lens review

The Lumix G 12.5mm f/12 3D lens, launched in 2010, was marketed as the world's first interchangeable 3D lens. It is currently available at a discounted price in some markets:


Physical

This is probably the simplest lens available for the Micro Four System so far. It is very small and light, and also, it has no moving parts whatsoever.

There is no focus mechanism. This is a so called fix focus lens. Fix focus lenses are typically seen in disposable cameras, cheap web cameras, and cheap mobile phone cameras.

Also, the lens is fix aperture, meaning that there is no aperture mechanism at all. There is only one aperture, f/12, and the lenses cannot be stopped down further.

At the fixed focus and aperture setting, the lens is in focus from 0.6m to infinity, according to the specifications.

There are two separate lenses, each of which has four lens elements in three groups. The stereo base, i.e., the distance between the lenses, is 1cm. For comparison, the stereo base of a typical human is around 8cm, which is the distance between the eyes. Hence, using this lens will give you significantly less 3D effect than what you are used to from your daily perspective.


Focal length and field of view

This lens is stated to have a focal length of 12.5mm. However, you should not let that fool you into thinking that this is a funky wide angle lens. Each of the two lenses project much smaller image circles onto the sensor, hence, there is another crop factor to take into consideration.

On the GH2 camera, the images created are 1920x1440 pixels, out of a total sensor area of 4608x3456 pixels. Hence, the crop factor of each projection is 2.4, and the field of view corresponds to a lens with a focal length of 30mm, e.g., the Sigma 30mm f/2.8 EX DN. So the 3D lens is actually a short tele lens.

This diagram illustrates the sensor sub areas used by the 3D lens:


The lens only uses 35% of the total sensor area, which helps to explain the limited resolution of the resulting 3D images, more about that later.

You can also choose to cover the electrical contacts of the lens, and use the full sensor output. Them you need to convert the image to 3D manually, but the advantage is that you get a much larger resolution to work with, around 2000x3000 pixels for each of the stereo pair image. Your image will be in portrait format.

Compatibility

As this lens was launched after the first wave of Micro Four Thirds cameras, it cannot be used on all of them. The first generation of Panasonic cameras can't use this lens, i.e., the G1, GH1, and GF1. Newer cameras can use the lens, however.

The Olympus E-P1, E-P2, E-P3, E-PL1, E-PL2, E-PL3, and E-PM1 cameras cannot use this lens. The OM-D E-M5 can, however.

Video

Contrary to what you might expect, you cannot record video using this lens. Not with any of the current cameras available, anyway.

Although it does not officially support video, there is nothing stopping you from covering up the electrical contacts of the lens, and then recording the video the camera sees through the 3D lens. I have demonstrated that here.

Use of the 3D images

When taking pictures using this lens, you get two image files. The first is an ordinary JPEG file, with the image from one of the lenses. When using a GH2 camera in the ordinary 4:3 aspect ratio, these images are 1920x1440 pixels, and are generally around 1.5 megabytes in size.

The second file has the .MPO suffix, and is a container file with two JPEG images, one from each lens. Both images are 1920x1440 pixels (when using the GH2 camera), and is around 3 megabytes in size.

If you have a Panasonic 3D TV set, it is pretty easy to display the MPO images on it, and there is indeed a 3D effect to them.

On other TV sets, this might be more difficult. Honestly, I don't have much experience with this.

On a PC, you could choose various different ways to display 3D images, depending on your hardware and preferences. I've chosen to use the Gimp plugin script-fu-make-anaglyph, which takes a pair of images, and turns them into a cyan/red image to be viewed using anaglyphic glasses. See the "Example images" section below.

Example images

This image was taken outdoors on the Intrepid Carrier Flight Deck. It was taken with the GH2 at ISO 160, f/12, 1/400s. The images are straight from the camera with no processing. Click for larger images.

left imageright image

And here is the anaglyphic version of the same image:


Another example, this image was taken indoors, at ISO 320, f/12, 1/60s, and with the onboard flash. The image depicts a LEGO model of the Intrepid carrier, inside the carrier itself. There is a large window letting in light from the side, but the lightning is still quite dim.

left imageright image

And here is the anaglyphic version of the same image:


In the last example, the 3D effect is more dominating, due to the shorter distance to the subject. For the best 3D effect, it is good to leave some items in the foreground, preferably around two feet out from your position, or thereabouts.

Close up use

According to the specifications, the lens can be used from 0.6m to infinity. At 0.6m focus distance, you can photograph items that are about 33cm by 25cm, which is not very impressive. Most lenses can photograph smaller items than this.

As this lens has no focus mechanism at all, there is no way for the camera to know at what distance your subject is. So you may very well ignore the 0.6m close limit, and photograph items that are closer. The disadvantage is that any items closer than 0.6m will be somewhat out of focus.

This is demonstrated here, where I have a focus distance of 0.2m to the central LEGO figure. For lightning, I used the Panasonic FL360 flash unit with a large diffusor.

left imageright image

And here is the anaglyphic version of the same image:


As you can see, the image is rather out of focus. It is probably best to avoid going this much outside of the lens focus distance specifications.

Conclusion

This lens has a short stereo base, hence, the stereo effect is rather limited. Also, it has a very small aperture at f/12. This restricts the lens to being used outdoors at daylight, or with a flash at a short distance.

The short stereo base could have made more sense for close up images, but the lack of a focus mechanism limits it to a distance of 0.6m and more. Even when used on a camera with a good resolution, the resolution of the 3D images is quite small.

And it is not possible to record 3D videos with this lens.

So is there anything positive to say about this lens? It can be an easy way to create some crude 3D images to show on your television. But my conclusion remains:

Don't buy this lens. Even at the discounted price you can find in some markets these days, it is not worth it, in my opinion.

If you are genuinely interested in 3D imaging, it is better to get one of the 3D compact cameras. Both Panasonic and Fujifilm market some compact cameras with two separate lenses, and two separate sensors, at a more sensible stereo distance of around 5-10 cm. These cameras give a better resolution, a zoom, a larger aperture, and can be used to record 3D videos. So they are better in every conceivable way than using the 3D lens on a Micro Four Thirds camera.