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[OM] Re: Depth of Field

Subject: [OM] Re: Depth of Field
From: Moose <olymoose@xxxxxxxxx>
Date: Tue, 20 Jun 2006 13:51:55 -0700
ALI wrote:
> Quoting Mike Lees <olympus@xxxxxxxxxxxxxx>:
>
> You can change the 'WB' balance to show DoF - just found this out. I am 
> sure if
> I have a good example yet but perhaps this is close:
>
> http://flickr.com/photos/4love/167337504/
>
> Its not sharp edge to edge. 
Looking at this shot, there are some simple pieces of technique you can 
use to improve your results.

1. First, you didn't really shoot for DOF. This shot is 35mm at f6.7, 
1/320 and iso 100. At 35 mm fl, you shouldn't need 1/320 shutter speed 
and you might prefer a sharp image to lowest possible noise. Just a 
small change to 1/160 and iso 200 would have given f13, and much more 
DOF, probably enough with the other two changes. Unless it was windy, I 
would also have tried a slower shutter speed and/or higher iso to get to 
f16.

2. It appears that you haven't used the DOF to best advantage. DOF 
extends both forward and back from the focal plane. It's not quite 
symmetrical, but pretty close. It appears clear that the closest point 
of the flower is in focus and the sharpness gradually decreases with 
increasing distance from the lens.

This means that roughly half of the relatively sharp zone is out in the 
air between the front of the flower and the lens. If you had focused 
slightly further out, between the front of the flower and the petals, 
you would find you had a deeper area in focus to work with. With some 
subjects, you can find something at the center of the DOF you want to 
let the AF focus on. With many, you need to go manual focus. A big 
advantage of doing this with digital is that one may shoot a series with 
very slightly different focal points and pick the best later.

3. Another thing I notice is that the petals on the right of the image 
are sharper than those on the left. This means you didn't have the 
camera square to the subject. Setting up so that the plane of focus is 
parallel to those things you want in focus makes better use of limited DOF.

Hard to say for sure, but I'll bet using the above techniques would have 
given you a shot with DOF and sharpness that pleased you.

DOF preview is nice, but of limited practical use when stopped way down. 
The viewfinder just gets too dim.
> I have another shot of a chicken - in which the head of the chicken is clear 
> but further down the neck is fuzzy. 
Sounds like similar things were happening there.

Someone else mentioned the technique of combining shots taken at 
different focal distances. This can work, but is a little fussy to do by 
hand because any change in focal distance also changes image size. 
That's usually not obvious - until you are trying to match up two shots 
at full pixel detail. Here are some two shot combos I've done. The way 
the stamens protrude so far, it's impossible to get everything in focus 
in one shot, at least with any equipment I have.

http://galleries.moosemystic.net/GGPark/Flowers/pages/FL25.htm
http://galleries.moosemystic.net/GGPark/Flowers/pages/FL27.htm
http://galleries.moosemystic.net/GGPark/Flowers/pages/FL34.htm

I'm pretty sure you don't need this technique for flowers like the 
daisy. Even this flower came out pretty sharp overall in one shot. The 
slightly greater subject distance, slight angle on the subject and the 
droopy stamen worked in my favor. This was 50mm @ f13 
<http://galleries.moosemystic.net/GGPark/Flowers/pages/FL30.htm>. Of 
course, the stamen isn't really particularly sharp, but at web size, it 
looks pretty good.

Moose

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