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[OM] Focus stacking

Subject: [OM] Focus stacking
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Wed, 30 Apr 2008 18:05:37 -0400
Quite some time ago I downloaded some free software that does image 
stacking ("CombineZM" by Alan Hadley) but never tried to use or study 
it.  CombineZM can be used to stack images for improved depth of field, 
add exposures (as in astrowork), increase dynamic range, etc. (yes, 
there's more)

Today I noticed the beautiful blossoms on a crabapple tree so snipped 
off a small branch and setup indoors to take a series of shots with a 
Viv Series 1 90/2.5 macro intending to get all of the blossoms in focus 
across the full width of the branch.  I ended up with a set of 7 frames 
each focused about an inch apart.  I started to peruse the instructions 
which seemed rather daunting so decided simply to press ahead and see if 
I could find the automated procedures.  I did but they made a perfect 
mess of the result.

First, I knew that changes in focus were going to cause slight 
differences in magnification.  But I was surprised to see just how much 
the magnification does change.  Across the full 7 frames the image 
shrank about 3-4%.  When I directed the software to do it's thing I 
ended up with a series of overlaid images all of slightly different 
size.  Not what I expected.  I guess I may be forced to read the 
instructions to figure out how to resize the images for a precise overlay.

Finally, and I don't know how I'm going to defeat this part, I noticed 
that over the 7 minutes I took to take the 7 shots that several blossoms 
visibly wilted during the session and sagged on their stems by roughly 
their own full width in the 7 minute session.  Guess I'm going to have 
to get faster.

Anyhow, anyone have any experience in doing this sort of thing.  Any advice?

Thanks,
Chuck Norcutt

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