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02-02-2020, 06:38 PM   #1
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Lightbox, trying for macro/max DoF on lava rock

Hi all. I have a piece of nice bubbly lava from a recent (1974) eruption, and I have been trying to get some nice sharp images with as much depth as possible. The rock also has some very nice iridescence and coloration to it which I'm also trying to capture as best I can. I am using one of those portable light boxes with USB-powered LED lighting, plus a fairly powerful hand-held flashlight for extra illumination. Camera is my K-50, 18-135WR mounted, on a GorillaPod, shutter on 2-second delay. Manual Focus & ISO at 100 for all.

In Av mode, I set aperture to maximum 40, and let it set the speed. Things came out too dark (black rock on white background I imagine), so I went to Manual and started fiddling with it there. Finally got some shots that are good for exposure, but the focus is still just a little bit off (even using Live View and the magnified view). I had hoped that setting f/40 would compensate enough, but alas it did not.

Open to suggestions... Would it increase my DOF if I changed over to my 70-300 with its 'macro' option? Have to back it away from the subject to be in the range, so maybe depth would increase? I like the image quality from the 18-135, but if stays so shallow on depth that I cannot get the right focus... (Old crappy eyeballs don't help)

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02-02-2020, 07:28 PM - 1 Like   #2
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Shallow DoF is typical when working at such a close range. To get around this you'll need to focus stack. I've never done any myself, but it involves taking many images focused differently through the whole depth of the subject and combining in post. Searching for "focus stacking" here should get you heading in the right direction.
02-02-2020, 11:58 PM   #3
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You may want to try using a grey card for setting the exposure. That will get you closer with a lot less time spent on tweaking.

Focus stacking pretty much is the only way to go to get more depth of field,

The GorillaPod may not be robust enough for you to get the best results with stacking.
02-03-2020, 08:43 AM - 1 Like   #4
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Hmm, ok. I had really hoped to avoid the focus stacking (like Homer Simpson, I feel like something old drips out my ears when something new gets shoved into my brain). We’ll see. And I’ll swap over to the big tripod once I clear some room...

Gracias.

02-03-2020, 08:47 AM - 1 Like   #5
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QuoteOriginally posted by RoxnDox Quote
In Av mode, I set aperture to maximum 40
I didn't know the 18-135 could go to f/40. I just tried mine on the K-3, and could get f/38 at the longest focal length.

In any case, though, unless you are desperate for depth of field over sharpness (try focus stacking, as mentioned above), I wouldn't go much smaller than f/11 (maybe f/16) with an APS-C sensor. You will be losing resolution to diffraction (https://photographylife.com/what-is-diffraction-in-photography, or Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks). For absolute best sharpness, f/8 is about the limit. You gain another stop (to f/11, say) for full-frame till diffraction starts to show up.
02-03-2020, 12:01 PM   #6
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QuoteOriginally posted by RoxnDox Quote
Hmm, ok. I had really hoped to avoid the focus stacking (like Homer Simpson, I feel like something old drips out my ears when something new gets shoved into my brain). Well see. And Ill swap over to the big tripod once I clear some room...

Gracias.
Back off on the focal length, if possible. That should buy you some DOF at the expense of working distance. Creative framing might also help.


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02-06-2020, 03:00 AM   #7
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At f40/f38, are you not seeing softening from diffraction, rather than merely focus being 'off'? When playing with my macro lenses, I have done various tests focusing on a piece of graph paper set at an angle, and taking multiple shots at different f-stops, to see the depth of field change, and then the image soften a little from diffraction at smaller apertures. This gives you some idea of how much depth of field you are playing with, and you will also be able to see at what point diffraction is making it all too soft.
02-07-2020, 10:22 AM   #8
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Read up on focus stacking. It isn't especially difficult and doesn't require any specialized equipment (though it doesn't hurt to have a focusing rail) Using focus stacking allows you to use your lens at it's best aperture, and also control DOF very tightly.
If you are using recent Photoshop (I am using CS6, I'm pretty sure earlier versions did this), you can do focus stacking pretty much automatically. There are specialized programs that apparently do a better job, I haven't bothered to try them out.

---------- Post added Feb 7th, 2020 at 11:24 AM ----------

QuoteOriginally posted by stevebrot Quote
Back off on the focal length, if possible. That should buy you some DOF at the expense of working distance. Creative framing might also help.


Steve
My experience has been that within any given format, DOF is a product of reproduction ratio on the film/sensor and aperture, not distance from the camera.

02-07-2020, 10:35 AM   #9
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QuoteOriginally posted by Wheatfield Quote
My experience has been that within any given format, DOF is a product of reproduction ratio on the film/sensor and aperture, not distance from the camera.
That is my experience as well and why I suggested a shorter focal length.


Steve
02-07-2020, 06:03 PM   #10
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Thanks all. I have stuck with PS Elements on my PC (no stacking), so I ended up getting the Zerene Systems ZS software to try on my Mac. Using the software has been easier than trying to get the focus slices needed. Making progress, but I do have some banding of sharp and fuzzy segments. Much of which is, I'm afraid, due to my (censored) eyeballs and being able to focus properly. Some cringeworthy CA too, likely made worse by the white background.

At any rate, a couple of improved results:

With 70-300 @ 180mm, f/8, 1/10s, 11 stacked images


same lens @ 200mm, f/8, 1/20s
02-13-2020, 05:42 PM   #11
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Found a Tamron 90mm macro lens at a local store, so I bought it and a focusing rail system. This is a test shot, just handheld with ambient light on the store counter:

02-17-2020, 02:29 PM - 1 Like   #12
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Latest result this morning. Stacked 18 images together, from the K-50/90mm (f/8, 1/6s, ISO 400), in the ZS app on my Mac. Slight adjustments afterwards in Photos to saturation, sharpening, and lightened a touch.

02-17-2020, 09:46 PM   #13
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QuoteOriginally posted by RoxnDox Quote
Found a Tamron 90mm macro lens at a local store, so I bought it and a focusing rail system. This is a test shot, just handheld with ambient light on the store counter:
QuoteOriginally posted by RoxnDox Quote
Latest result this morning. Stacked 18 images together, from the K-50/90mm (f/8, 1/6s, ISO 400), in the ZS app on my Mac. Slight adjustments afterwards in Photos to saturation, sharpening, and lightened a touch.
Yay! Looking good!


Steve
02-18-2020, 07:53 AM   #14
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QuoteOriginally posted by RoxnDox Quote
Latest result this morning. Stacked 18 images together, from the K-50/90mm (f/8, 1/6s, ISO 400), in the ZS app on my Mac. Slight adjustments afterwards in Photos to saturation, sharpening, and lightened a touch.
QuoteOriginally posted by stevebrot Quote
Yay! Looking good!
Agreed
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