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Auto-focus or manual

by Benny Sutton

Reproduced from in focus 50 (January 1994)

The majority of underwater camera housing manufacturers have dropped manual focus altogether in favour of autofocus - but is this a good idea?

When autofocus first became widely available there was a lot of resistance to its use underwater. The purists condemned autofocus as being for beginners: real tough underwater photographers didn't use autofocus, did they?

It was a bit like the situation that arose when BCs took over from ABLJs, The mass of the buying public made up their own minds and voted with their pockets. So it was with autofocus and the purists missed photographic opportunities.

The general acceptance of autofocus meant that cameras with sports-finders became obsolete for underwater photography. You didn't need a large screen to focus anymore, and you also didn't need the huge housings that went with such cameras!

The Nikon F801 soon established itself as the world's most popular autofocus camera to house for underwater use, and it converted even the most sceptical. There were still a few of us, however, nostalgic for the good old days, who felt that there must still be a place for manual focus - but is there?

The short answer to the last question is no! Once you take the plunge into autofocus you eventually arrive at the conclusion that you are missing the point if you put a technologically advanced camera like the Nikon F90 or F801 in a housing and then start using it on manual focus. Underwater photography is difficult enough, so we should be looking for things that make it easier - not harder. Autofocus and auto-exposure controls are there to free the photographer to concentrate on finding the subjects and composing shots.

I had resisted the dreaded autofocus harder and longer than most, until one day I was under Swanage Pier (where else) photographing a Tompot Blenny (you know the one). He was being most co-operative, sticking his head out of his pipe and posing away. I was using a 60mm macro lens but it was so dark under the pier that, although I could make him out as being in frame, I was damned if I could see whether he was in focus or not! I went by the autofocus indicator and shot the roll off anyway. When the film was processed I had 36 in-focus shots.

Autofocus systems these days can not only see in less light than we can, they are also faster. try it yourself. Take an autofocus camera and try to manually focus on the opposite wall of the room (OK, you may not be in a room). Now swap to autofocus and see how much quicker it is. Now try the same exercise underwater with the camera in a housing when you're cold and wearing gloves. Case proven!

One situation in which autofocus does have difficulty is with subjects of low contrast (autofocus uses contrast to determine focus). However, your eyes also work on this principle which is why, if you can see a subject well enough to manually focus, then so will your autofocus system.

There are, however, ways around the problems of low contrast, should you encounter it. Take the practical situation of photographing a shark. If you are lucky enough to get close enough to one for photography, you will discover that its skin is so smooth that there is insufficient contrast for autofocus. You will need to find an edge, its fin perhaps, to use for autofocus (just like you would on manual with a split-screen focus system). Apart from flat walls (not an interesting subject) there is always an edge to use if you have insufficient subject contrast.

The only situation where you have neither an edge nor subject contrast is with some heavily back-lit subjects. Manual focusing may be just as hit and miss as autofocus in such circumstances. An equally valid alternative to manual focus therefore (with back-lit subjects) is to pre-focus on a convenient object and use the focus lock (by depressing the shutter release halfway) then allow the subject to come into range before firing. The depth of field on wide-angle lenses usually covers up any mistakes.

If you must swap between manual and autofocus modes underwater you should be aware that damage to your camera can result. Read your camera instruction manual carefully. Although the camera may allow you to swap between manual and autofocus modes, some lenses require additional adjustments (like the Autofocus - Manaul ring on the 60 mm Micro Nikkor which disengages the drive gearing) and you can't change the control whilst the camera is inside the housing.

Manual focusing of a camera in a housing also requires an additional gear to be fitted to the lens and all those gears create extra resistance for the autofocus drive motor to overcome. There is, therefore, the possibility that the extra loading (for which the motor was not designed) can also cause damage and leave you with a half functioning camera in the middle of nowhere!

You should then, for the sake of your drive gears, choose which focus mode you use before you get in the water and stick to it. Given the small percentage of shots that actually benefit from manual focus it should be obvious what the right choice is!

Remember, it is the contents of a picture that is judged - not how it was focused. Autofocus is not cheating - honest!

[Editor's note: I'm not sure that the majority of camera housing manufacturers have dropped manual focus altogether. Certainly the Subal housing for a Nikon F801 I purchased in the later half of 1993 has an external manual focus control and, moreover, this can be disengaged from the lens gear if you choose to use autofocus, putting no extra strain on the autofocus drive motor. Although the focus gear can be disengaged, it is still necessary, as Benny suggests to set the Autofocus - Manual ring to Autofocus on the 60 mm Micro Nikkor lens before putting the camera in a housing if you are intending to use autofocus.

In my opinion, sports-finders are still a very useful add-on. I much prefer to compose a shot with my Pentax LX and sports-finder in a Hugyfot housing than with my Nikon F801 in a Subal housing, if only because I can see the extreme edges of the frame and read the LEDs without squinting. Covering only about 92% of the picture area as it does, the Nikon F801's viewfinder has its limits, particularly inside a housing and viewed through a face mask.

I do use autofocus and am pleased with the results I have got. Ideally, however, I'd go for autofocus and a sportsfinder.]

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