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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.] |
