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Focusing Tecniques


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#1 Rob Esaw

Rob Esaw

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Posted 23 March 2003 - 10:00 PM

I found that it's strange having to be concerned with focus now that I've moved to a housing.

Before, I had a Nikonos V, and I thought the manual focus with no slr viewfinder sucked, and I couldn't wait until I moved up to digital to get that 'autofocus', yeh!

But, I am surprised to see that it's taking a great deal of effort to get a sharp shot. Please, any tips, if you have them.

One thing I thought I'd share is with a test dive I just took with my buddy and his new camera:

I found the autofocus didn't like anemone tentacles and the camera kept tracking back and forth from soft to sharp to soft, and just released way out of range. I guess the many different tentacles at different distances is too much for the focus to lock on.

One thing I tried was to lock focus BESIDE the subject at a similar distance, then recompose and shoot. I was concerned about being able to keep the same distance for a length of time while moving the camera, but I found that the depth of field is great enough with digital that it wasn't a problem.

I know you housing folk have probably done this before, but I'm a newby to anything beyond simple ttl and thought I'd show an example:

#2 Rob Esaw

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Posted 23 March 2003 - 10:02 PM

Above was the best I could get with the focus area selector on the anemone, and below was locked to the right of the subject, and then recomposed and shot.

Hope the examples are clear enough.

#3 scottyb

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Posted 24 March 2003 - 04:28 AM

Rob, I am going through the same learning curve. I found that once I locked the focus on the subject, you can tweak it by moving forward or backward slightly until you get the focus you like. Anemones and others with multiple targets present more of a problem. I wish I had MF for these times.

#4 chrisg

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Posted 24 March 2003 - 05:44 AM

I found that it's strange having to be concerned with focus now that I've moved to a housing.

Before, I had a Nikonos V, and I thought the manual focus with no slr viewfinder sucked, and I couldn't wait until I moved up to digital to get that 'autofocus', yeh!

But, I am surprised to see that it's taking a great deal of effort to get a sharp shot.  Please, any tips, if you have them.

One thing I thought I'd share is with a test dive I just took with my buddy and his new camera:

I found the autofocus didn't like anemone tentacles and the camera kept tracking back and forth from soft to sharp to soft, and just released way out of range.  I guess the many different tentacles at different distances is too much for the focus to lock on.

One thing I tried was to lock focus BESIDE the subject at a similar distance, then recompose and shoot.  I was concerned about being able to keep the same distance for a length of time while moving the camera, but I found that the depth of field is great enough with digital that it wasn't a problem.

I know you housing folk have probably done this before, but I'm a newby to anything beyond simple ttl and thought I'd show an example:

I use manual focus for pretty much anything except wide angle images in bright light. The technique I use is to mostly think of the manual focus control as a "subject size selector", rather than a means of focus. I remember what '"size" I am currently set for, and adjust if necessary while approaching the subject. Sometimes while between subjects, or during approach, I will place my hand some distance in front of the lens
to check current focus distance/subject size, and adjust.

When I am in front of the subject, I will usually swim until i'm close to the desired distance before I look through the view finder, peeking above the housing to keep the subject in view, making sure strobes are reasonably adjusted, etc. When I'm close to within range I look through the viewfinder, and adjust my position until I have the composition I want and then inch forward and back until i've got the focus right. If the focus is difficult and/or the subject is uncooperative (pygmy seahorses seem to instinctively turn away from cameras :-), and/or current is making things difficult, it may take some number of iterations of adjusting position. composing, and focusing before an opportunity to press the shutter release presents itself.