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.

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