In the family of wide angle lenses we have however one exception: the fisheye lens. This lens is not so commonly used; the prize is often higher compared to other wide angle lenses and it is generally considered as having very limited use. Already the name however, should make the diving photographer alert: Fisheye !

This type of lens produces extraordinary results at underwater photography. How come ? Part of the explanation is recognizable if you are aware of some properties of this lens type. Here are the most important:

• The fisheye lens has an angle of view of 180 degrees. There are two types of fisheye lenses. The subject here is the so called "full frame fisheye" lens, having this angle of view along the diagonal of the picture and thus "filling the full frame". We also have the second kind of fisheye lens, which is giving a round picture of 180 degrees, utilizing then only part of the film format. This lens is more specialised and perhaps of less interest.
• Straight lines are generally reproduced curved in the picture ("barrel shaped distortion").

You need more details to get the explanation:

Imagine yourself standing close to a straight railroad, looking perpendicularly to the rails through the viewfinder of your single-lens-reflex camera, having a lens with an angle of view of 180 degrees. You look at the rails, which are passing diagonally from one corner to the other.

What do you see ?

• It is a subject with two parallell straight objects, the rails.
• They are separated by a certain distance in the middle of the picture. Lens to subject distance is here typically a couple of meters.
• The distance between the rails diminish to zero at the corners, which represent a lens to subject distance of infinity.

Realising that this is a correct description of what you see, you now also realise, why the fisheye lens must have a "barrel shaped distortion", and why the conventional property of wide angle lenses: "straight lines remain straight" is impossible for fisheye lenses. It is also evident, why the "barrel shape" in this case is closer to a realistic reproduction than the "straight lines remain straight" of other wide angle lenses.

Having this perhaps new knowledge in mind, it is rather logical to think, that the planes of sharpness also could be different for fisheye lenses compared to other wide angle lenses. Conventional wide angle lenses are designed to reproduce flat subjects well on flat film. This means that they must handle a large variation in lens to subject distance, going from the middle of the picture to one corner (with respect to plane of sharpness). The larger the angle of view, the more difficult this will be. With an angle of view of 180 degrees, and small lens-to-subject distance in the middle of the picture, this is impossible (remember the rails!). Therefore fisheye lenses are designed to reproduce not flat, but curved objects sharply on the flat film surface. Now we have one important clue to the extraordinary results at underwater photography: the curvature of field and the reduced lens to image distance, produced by the dome port, is an ideal situation for the fisheye lens !

What about the "barrel shaped distortion" then, doesn't it cause a strange appearance for many subjects, making the use of the lens very limited ? Well, this is perhaps true for subjects containing straight lines, as for many "on land" subjects. Under water, however, straight lines are of a much smaller occurrence, not to say rare. You can take lots of pictures under water with a fisheye lens, without bothering about the distortion, the spectators will never notice.

Now that I have explained why the fisheye lens is superior to other housed camera wide-angle lenses, I must add that an alternative exist: the Nikonos system. The only way however to get comparable results with respect to resolution, is to use those lenses in the system, which are optically designed for underwater use.

Still not convinced ? Look at most of the published underwater pictures today, and/or try to borrow or rent a fisheye lens (with accessories).

*) "Housed cameras" are cameras with a surrounding waterproof housing.

We have discussed an ideal lens type for underwater photography, a most important factor striving against the ultimate underwater photograph. An other factor, that can improve the situation considerably, is a larger film format (it has been understood, that the discussion so far has dealt with the 35 mm film format). It is easy to understand, that a larger film format does not need as much magnification as a smaller for the same picture size, and hence the quality should be better. It is however first when you see slide shows with similar subjects but different film format that you really realise how big the difference is. It is not only a difference in the ability to resolve small details, it is also something with the colours, that is more difficult to pinpoint. Colours are more vivid and seem to have "larger span". It is necessary to experience this, it is difficult to explain. This difference can not be fully compensated by increased lens quality for the smaller format, which has been claimed by some 35 mm fans. I have personal experience from comparisons between Canon EF 35 mm lenses (top-rated by many photographers) and Mamiya lenses (for the 6x4.5 cm format).

What about depth of field then, the larger format must lag behind because of larger focal lengths for the lenses ? Yes, this is true, but not as much as the difference in focal length indicate. The reason is the smaller need for magnification. The smallest medium size format (6x4.5 cm) is in this respect ideal; a fisheye lens has a focal length of 24 mm, resulting in completely satisfactory depth of field. Going to macro photography will also be without problems with respect to depth of field. I have personal experience of using 80 and 120 mm macro lenses, reproduction ratios down to 1:1. Macro lenses by the way, do not need, and should not be provided with, a dome port. The reason is their limited angle of view and the "long travel" of the lens package at focusing.

I have already discussed lens selection for underwater photography and medium size format: the fisheye lens of course, and the macro lens. To get those corner-to-corner pinsharp pictures I have no other realistic suggestion for you; lenses of in-between focal lengths are super-wide or wide-angle lenses, and as such they have problems with the curvature of field produced by the dome (not to mention the shortcomings of the flat port). An alternative has however existed for Hasselblad photographers. About ten years ago it was possible to purchase a so called Ivanoff corrector, manufactured by Zeiss, to the Super Wide Camera and the 38 mm Biogon lens. This combination is really a high quality performer. Unfortunately I don't think it is possible to get one today (the prize was also extraordinary!).

How about the bulkiness of medium size format cameras ? It is true that they are larger and heavier, and they also most often need a tripod at normal photography. Under water however, they are just as easy (or even easier) to handle, compared to a 35 mm camera, if the housing is designed to be neutrally buoyant and with ergonomy in mind.

What about number of frames per film then, 12 or 15 must be too small ? Well, actually you are better off, compared to a 35 mm camera. You don't have to use 120 roll film, you have the possibility to use 220 instead, having around 30 frames, which is quite in level with the 36 frames of a 35mm film. Sometimes it is quite sufficiant to use the 120 roll film. Have you ever been in the situation, when you have exposed only half your 35mm film, but are impatient to see the result ?

Competing with other photographers regarding the attention of picture editors of magazines and newspapers, you have a great advantage over 35mm collegues, if you use medium size. The editors are often middle age, and they have difficulties seeing those small 35mm slides ! (As long as the pictures are provided as slides, digitalized pictures is an other matter !)

I am personnally convinced, that one of my greatest victories in an UW photo competition, to a large extent depended on my medium size format slides !

So, being an underwater photographer with ambitions, take a close look at the possibilities, properties and economy of medium size format lenses (fisheye, macro) and cameras. Personnaly I have realised following, and I only regret that I didn't understand it long time ago: It is a waist of time, money, efforts and especially those once-in-a-lifetime-shots not to use the superior medium size format !

Here are some useful links, if you want to look at some medium format camera systems, suitable for underwater photography (fisheye lens included in the system):