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FORUMS Photography Talk by Genre Macro Talk
Thread started 07 May 2009 (Thursday) 14:05
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Photoshop CS4 Focus Stacking with manual mask work afterwards

 
Triptoph
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May 23, 2009 18:32 |  #16

Wow, now that's support!

Thank you Rik for your insight. I thought 11 shots would be enough for this subject as it was a few centimeters long, however the aperture was probably a bit wide looking back. The MPE-65 lens I've used here is very new to me, I'm still learning the ropes. I may try this shot again when I find another poppy seed, I've got a much better working setup now than I did then, and a little bit more experience under my belt. I'm sure that you're right in that a good part of the poor results here was from my own inexperience.

I'm currently working on another image stack and have similar problems, though not nearly as pronounced. Will post results another day.

Cheers,

Tony


-Tony

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rjlittlefield
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May 23, 2009 22:37 as a reply to Triptoph's post |  #17

Tony, you're very welcome. Between answering the support email for Zerene Stacker, and having done high mag stacking myself for over 5 years, I have a pretty good appreciation for what all can go wrong. There's quite a lot.

Most people don't realize how shallow DOF gets at higher magnification.

The standard formula (from Lefkowitz) is that TDF = 2*C*fr*(m+1)/(m*m), where TDF is total depth of field, C is the circle of confusion (typically sensor diagonal/1500), fr is the f-number set on the lens ring, and m is the magnification.

If you crunch through the numbers, using say a 1.6 crop-factor DSLR (C=0.018 mm), at 1:1 (m=1) and f/16 (fr=16), you get only about 1.2 mm TDF. Generally it's a good idea to have 20% overlap or so for stacking, so figure 1 mm per focus step. That's at 1:1 and f/16.

At higher magnifications, the problem gets worse by a factor of almost m*m because you also have to open up the aperture to avoid too much diffraction blur. At 5:1 and a lens setting of f/5.6, TDF = 0.05 mm, about 0.002 inch. This is why the stacking discussions at photomacrography.net talk so much about screw tables and even finer positioners.

My offer to help still stands. That's a nice image you're working on, and I'd like to see it come out well. Besides, I learn something every time I help work through one of these problems.

Best regards,
Rik Littlefield
Zerene Systems




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Triptoph
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May 23, 2009 23:51 |  #18

At 0.05mm, that would be 1/25th of a turn on the screw on my focusing rail (RSS B-150B), with a 20% overlap, 1/30th. Yikes. I wish it had exact degrees marked out on it, perhaps I can modify it and add some kind of dial that shows degrees on it.

I think that particular subject is a lost cause as the poppy is long gone now, might get another later though and try again.


-Tony

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Triptoph
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May 24, 2009 01:13 |  #19

100% crop of a photo of the center of a pansy. There is a problem with CS4 in that it seems to assume that the focus drops off gradually throughout the image, resulting in halos around areas that change in DOF quickly, if you know what I mean. These images are from a stack of 12 photos, one processed in CS4 using Blend Layers with Seamless Tones and Colours option enabled, and the other in Zerene Stacker using PMax.

Especially when seeing the full image at 100% on a 30" display there is no real competition here, the ZS image is clearly sharper without the troublesome halo effect. My fiancée who knows little about photography at all, just took a look at the two and said "wow that one is so much better." So I know it's not just me. Hope this comparison shows the issue I'm talking about. No PP has been done other than stacking on purpose.

Still working on the final image, will post it in the Macro sharing forum when finished :)

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-Tony

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Triptoph
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May 24, 2009 13:29 |  #20

Final image: http://photography-on-the.net/forum/showthre​ad.php?t=698676


-Tony

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Photoshop CS4 Focus Stacking with manual mask work afterwards
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