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09-03-2010, 05:00 AM   #1
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macro advice needed for low apertures (e.g. f/22)

Dear all,

my father is a long time Pentax user. He mostly shots scientific-purpose close-up pictures of fungi and flora in the wood, and in order to get very clear and descriptive images he needs to use very low apertures around f/22.
He used to use both a Pentax-A 50mm f/2.8 and a Pentax-M 50mm f/4 with excellent result on film, but now with his K20D the results are much less impressive.
I know that there's a diffraction problem on the K20D (and other DSLRs) when closing over f/11, and in fact the pictures using f/11 are much better... however, he needs everything on focus (scientific purpose) and f/11 is not enough for close ups.
Do you have any advice on how to improve his results?
Thanks in advance


Last edited by noou; 09-12-2010 at 06:29 AM. Reason: improved title
09-03-2010, 05:13 AM   #2
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QuoteQuote:
I know that there's a diffraction problem on the K20D (and other DSLRs) when closing over f/11
This will happen with all cameras, diffraction is a property of the lens, not the sensor.

What might happen is that his lenses are not telecentric. The sensor on a DSLR has more trouble accepting light arriving at strong angles, it's better at collecting light hitting it perpenticular to its surface. Film is better for this.

A lens designed for digital will take this into account, and be telecentric, which will help, indeed. But it should not have that much of an impact on resolution.

I suspect, since your father is using manual focus lenses, that he's simply having trouble focusing his lenses on a digital body. The viewfinder is much smaller, it's harder to tell if the subject is in focus.

A couple of solutions could be:

1-purchase a focus screen

2-use live view to focus

3-Get an AF lens.

I hope this helps!
09-03-2010, 05:23 AM   #3
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QuoteOriginally posted by bdery Quote
This will happen with all cameras, diffraction is a property of the lens, not the sensor.

What might happen is that his lenses are not telecentric. The sensor on a DSLR has more trouble accepting light arriving at strong angles, it's better at collecting light hitting it perpenticular to its surface. Film is better for this.

A lens designed for digital will take this into account, and be telecentric, which will help, indeed. But it should not have that much of an impact on resolution.

I suspect, since your father is using manual focus lenses, that he's simply having trouble focusing his lenses on a digital body. The viewfinder is much smaller, it's harder to tell if the subject is in focus.

A couple of solutions could be:

1-purchase a focus screen

2-use live view to focus

3-Get an AF lens.

I hope this helps!
thanks bdery, very interesting points! In particular, the "perpendicular issue" is really worth checking.

Indeed my father's focusing skills have worsen with the K20D's VF (and his age) However, I've shot myself some pictures together with him (and I corrected the focus), in order to verify the impact of different apertures. What I found is that below f/11 (e.g. f/22) the pictures lack resolution, they are so to say more flou-ed.
09-03-2010, 05:44 AM   #4
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In reading this, I have a few comments

First of all, I suspect that part of the problem may be post processing, in terms of getting the colors etc just right.

with respect to the issue of the lens needing to be "telecentric", and having light hit at a higher angle, this should not impact center sharpness, but causes vignetting at the edges. as most light hitting the center of the sensor is already at a high angle. Additionally, this issue was more of a problem with older , i.e. first generation , sensors than newer ones which use micro lenses, and is an issue at wide angles prodominantly, not normal to tele, or macro.

Defraction is an issue, and the impact has increased with digital (especially APS_C sensors) because we enlarge the images more to get the same results, specifically, if you fill the frame with a flower, on film, and then fill the frame on an ASP-C sensor, to get to the same size print, you are enlarging the image more. (the only way to compare apples to apples in this respect is if you are always using a fixed magnification ratio on the lens, and cropping down in either format to get the final image.

With respect to the view-finder, the K20 has a nice bright finder but it is optimized for F4-5.6 and has a misleading DOF, which can fool you on focusing. You need to consider 2 things here, selecting the focus sensor you want, as opposed to auto, and using the focus confirmation. Combination of beep and green hexagon in the bottom of the viewfinder, for focus. Or a split image finder, which is better.

other than these points, macro should not be an issue, as many posters here have produced stunning shots.

09-03-2010, 06:13 AM   #5
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Use Live View to focus, then select info to zoom to 4x or 8x. You'll see right away what you need to do to focus.
09-03-2010, 06:46 AM   #6
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The over-riding concern with tiny apertures is getting sufficient light on the subject. Is he using some sort of artificial light source for his work; flash, lamps, etc? Is he using a tripod? Even a tripod won't always help. Flora is often not a still subject. A light breeze makes macro shooting considerably more challenging

DSLR shooters regularly use f14-f32 for macros and diffraction is not the big concern. Yes, it causes a bit of IQ loss, but it's nowhere near as worrisome as the battle between depth of field and shutter speed. I'll compromise on ISO any time if it means keeping a good shutter speed. Motion blur or camera shake means a spoiled photo. Digital noise can be managed.
09-03-2010, 09:34 AM   #7
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just like to throw in that stacking several (two even) images at lower F-stops together will give you more DOF than he will ever have with F/22 and MUCH more IQ.

Last edited by yeatzee; 09-03-2010 at 10:19 AM.
09-03-2010, 10:05 AM   #8
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I do a lot of macros of tiny wildflowers with a K20D and a DA 35mm macro Limited and have developed a method that gets maximum detail and sharpness at f-22. To see what I mean, google Ron Kruger and click on any link to Photoshelter, then click on Tiny Wildflower Macros. If you or your father are intested, contact me though my website and I'll share my method.

09-03-2010, 10:47 AM   #9
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Forgive me if I'm totally off here but are you controlling the ISO to keep it low-ish?
09-03-2010, 10:54 AM   #10
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QuoteOriginally posted by lowspark86 Quote
Forgive me if I'm totally off here but are you controlling the ISO to keep it low-ish?
sure, he always shots at 100 or 200 iso max.
Since in the wood it's dark, he uses an all-metal professional tripod, with hooked legs in order to be better anchored to the ground. He always did like this when he use to shoot film.

Believe me, it's not a matter of quality in general: as I said the results are very good at f/8-11, except for the fact that not everything is focused. The problem manifests just when closing down.
09-03-2010, 10:55 AM   #11
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Also, I'm wondering how you are comparing the film results to the digital results. I'll be naive and guess maybe comparing a 4x6 print to a 100% view on a computer monitor (which is enlarged about a hundred times more than the 4x6 print), and that could have something to do with the perception that the results aren't as sharp. What about comparing prints of the same size. OK, maybe you are doing this already. But I thought I'd at least mention that, as it's actually a pretty common way to get misled.
09-03-2010, 10:56 AM   #12
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QuoteOriginally posted by yeatzee Quote
just like to throw in that stacking several (two even) images at lower F-stops together will give you more DOF than he will ever have with F/22 and MUCH more IQ.
I see, and I'm sure you're right. But I'm trying to address an issue at its lowest level here: f/22 (even f/32 with the Pentax-M 50mm f/4 macro) was excellent on film.

Last edited by noou; 09-03-2010 at 11:16 AM.
09-03-2010, 11:05 AM   #13
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QuoteOriginally posted by Marc Sabatella Quote
Also, I'm wondering how you are comparing the film results to the digital results. I'll be naive and guess maybe comparing a 4x6 print to a 100% view on a computer monitor (which is enlarged about a hundred times more than the 4x6 print), and that could have something to do with the perception that the results aren't as sharp. What about comparing prints of the same size. OK, maybe you are doing this already. But I thought I'd at least mention that, as it's actually a pretty common way to get misled.
we compare his images printed professionally in the same book/calendar/magazine for instance.
The film version (slide film, actually) is always digitized at 300dpi with a professional (and expensive!) cylinder scanner.
Both the digital and the film versions are never cropped.
Of course looking at the slide shot on a computer monitor it looks more grainy.

Still, what I don't understand is why his beautiful macro lens on the K20D is softer at f/22 than at f/11.
09-03-2010, 11:14 AM   #14
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QuoteOriginally posted by Ron Kruger Quote
I do a lot of macros of tiny wildflowers with a K20D and a DA 35mm macro Limited and have developed a method that gets maximum detail and sharpness at f-22. To see what I mean, google Ron Kruger and click on any link to Photoshelter, then click on Tiny Wildflower Macros. If you or your father are intested, contact me though my website and I'll share my method.
thanks Ron. I looked at some pictures there, but I'm not sure I can find shots taken at f/22. Most of them have a dof surely shallower than what you get at f/22. Could you show me (even via pm) a few examples?
For instance this Wild Mushrooms and Plants | Ron Kruger Outdoor Photography is indeed nice, but totally useless for scientific purposes, where every detail must be clear.
09-03-2010, 11:17 AM   #15
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QuoteOriginally posted by Marc Sabatella Quote
Also, I'm wondering how you are comparing the film results to the digital results. I'll be naive and guess maybe comparing a 4x6 print to a 100% view on a computer monitor (which is enlarged about a hundred times more than the 4x6 print), and that could have something to do with the perception that the results aren't as sharp. What about comparing prints of the same size. OK, maybe you are doing this already. But I thought I'd at least mention that, as it's actually a pretty common way to get misled.
QuoteOriginally posted by noou Quote
we compare his images printed professionally in the same book/calendar/magazine for instance.
The film version (slide film, actually) is always digitized at 300dpi with a professional (and expensive!) cylinder scanner.
Both the digital and the film versions are never cropped.
Of course looking at the slide shot on a computer monitor it looks more grainy.

Still, what I don't understand is why his beautiful macro lens on the K20D is softer at f/22 than at f/11.
the point is, I think, that who ever edited and scanned the images probably did a ton of post processing to print in a magazine, on top of what ever processing, contrast and lighting adjustment the person who printed the shot origonally did,

It is hard to compare a 1:1 on this basis.
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