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10-25-2010, 04:19 PM   #1
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macro test target?

I'd appreciate suggestions for a good test target for high magnification macro resolution testing.

The tests are to see how magnification and f-stop affect the diffraction limit.

One kind of ideal target would be fractal in nature, such that it would appear to have the same granularity at all magnifications. Another would be ruled at 1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, 1/128, 1/256, ... mm spacing.

A perfectly sharp edge jumping from black to white might work too, but where to find such an edge? Maybe a razor blade suspended well in front of an illuminated field?

What are your thoughts?

Dave

PS I think diffraction theory implies a maximum usable macro magnification of about:

mag_max ~ 24/f-stop - 1

That's when a diffraction spot occupies about one pixel on a thousand pixel wide display.

10-25-2010, 04:52 PM   #2
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Honestly, my thoughts are go out and take some pictures.
10-25-2010, 05:21 PM   #3
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QuoteOriginally posted by Wheatfield Quote
Honestly, my thoughts are go out and take some pictures.
Just taking random pictures isn't too efficient when trying to do quantitative comparisons. The object should be at least as controlled as the other parameters when trying to document the effects of parameter variation on the image, else one can't be certain if changes on the image are due to the object or some other parameter variation.

Or are you trying to tell me measurements are a waste of time compared to other activities? For you maybe yes, for me, not at all.

Dave
10-25-2010, 05:34 PM   #4
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Flower petals have details within details; perhaps if lighting is too variable you could bring a few inside. Many have more curvature than you seek, but I've a hydrangea with pretty flat petals that would show intricate detail on several levels.

A poor shot of a good candidate:


10-25-2010, 05:44 PM   #5
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I do a lot of macro, and from practical experiements, I'm convinced that the degree of diffraction is not just determined by the f-stop, but by the intensity of light as well. I shoot at f-22 all the time with my DA 35mm macro Limited, but I fill with bounced and diffused light that is intensly concentrated on the subject. To see this, Google Ron Kruger and click on any link to Photoshelter. Then click on Tiny Wildflower Macros. All but a very few in there were shot at f-22.
10-25-2010, 07:22 PM   #6
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QuoteOriginally posted by newarts Quote
Just taking random pictures isn't too efficient when trying to do quantitative comparisons. The object should be at least as controlled as the other parameters when trying to document the effects of parameter variation on the image, else one can't be certain if changes on the image are due to the object or some other parameter variation.

Or are you trying to tell me measurements are a waste of time compared to other activities? For you maybe yes, for me, not at all.

Dave
I've never seen a picture of a test target that caused me an emotional response.
I think people are getting far too tied up with quantitative measurements when they could be spending their time making pictures.
I'm not being facetious, Go out and take pictures, see what works in the real world, you might be very surprised.
10-26-2010, 05:17 AM   #7
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QuoteOriginally posted by Wheatfield Quote
I've never seen a picture of a test target that caused me an emotional response..
Nor have I.

Neither have I seen a collection of random photos that convinced me maximum useful macro magnification depends only on f-stop according to an easy to remember relationship.

Not long ago a poster asked if there is a limit to optical magnification for macros; I don't think "Go thee and take some photos!" is a sufficient answer; rather, such an answer is an insult to the original poster.

I feel satisfied when I can answer such questions in a manner useful to an average photographer.

Dave
10-26-2010, 05:31 AM   #8
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QuoteOriginally posted by newarts Quote
Nor have I.

Neither have I seen a collection of random photos that convinced me maximum useful macro magnification depends only on f-stop according to an easy to remember relationship.

Not long ago a poster asked if there is a limit to optical magnification for macros; I don't think "Go thee and take some photos!" is a sufficient answer; rather, such an answer is an insult to the original poster.

I feel satisfied when I can answer such questions in a manner useful to an average photographer.

Dave
but the question is, exactly what are you going to do with the information.

You will get an answer that shows how defraction degrades the performance of the lens, when shooting a flat surface. OK so it tells you where the limit is for copy purposes, and if you are shooting stamps or coins, that can be important.

BUT when shooting a 3 dimensional object, you have to decide the trade off of loss of sharpness with defraction, and loss of depth of field when you try to avoid defraction.

I think the best way to judge is as suggested. Look at a flower petal, it has very intricate details from the range of normal to maco to micro. Set up the picture so that you have one petal flat (relitive to sensor) and have the rest at different focusing planes. Take a series of shots, and compare the detail in the petal. then look at the rest of the image, where has defraction hurt in extreme detail but depth of feild gained in overall image. Pick the compromise you like the best

10-26-2010, 05:35 AM   #9
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QuoteOriginally posted by Wheatfield Quote
I've never seen a picture of a test target that caused me an emotional response.
COme on now, you mean my bland shots of a block wall to calibrate exposure don't make you cry?
QuoteQuote:
I think people are getting far too tied up with quantitative measurements when they could be spending their time making pictures.
I agree. there are measurements you need to take to quantify you rgear, in terms of exposure, and perhaps some for focus, mostly to ensure that when you go out, you get both exposure and focus where you want them, so you can concentrate on composition
QuoteQuote:
I'm not being facetious, Go out and take pictures, see what works in the real world, you might be very surprised.
No way. you mean use a camera for what it was made for?

+1, agree totally
10-26-2010, 06:40 AM   #10
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You people (Lowell and Wheatsfield) are amazing!

You would deny me the pleasure of establishing valid relationships to aid others?

Yet you happily use similar exposure relationships developed by others though theory and experiment?

And your answer to a simple question concerning macro photo magnification limits remains "go take some photos?" Uh, that's no answer at all unless you mean that everyone must discover underlying principles through personal trial and error.

QuoteOriginally posted by Lowell says:
... there are measurements you need to take to quantify you rgear, in terms of exposure, and perhaps some for focus, mostly to ensure that when you go out, you get both exposure and focus where you want them, so you can concentrate on composition.
I'm not advocating that individuals in general make measurements "to quantify your gear" - that seems to be what you are recommending; and that is terribly inefficient; rather, I seek to provide some simple guidelines to aid in the process of macro photography to avoid everyone's re-inventing the wheel.

Dave
10-26-2010, 12:37 PM   #11
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That being the case, I suspect you are going to be looking for a plate that has lines etched in by a laser.
When you find one, I'd be interested to know what it cost and whether or not it provided what you needed.
10-27-2010, 04:12 AM   #12
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QuoteOriginally posted by Wheatfield Quote
That being the case, I suspect you are going to be looking for a plate that has lines etched in by a laser.
When you find one, I'd be interested to know what it cost and whether or not it provided what you needed.
Such calibrated scales are in the $500's-$5000's range!

I'm thinking that natural targets like the plant leaves mentioned earlier might be good at least for a series of macros at a particular magnification with varying f-number.

I'd likely be best off to quit talking and start doing, just like you said.

Dave
10-27-2010, 05:23 AM   #13
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QuoteOriginally posted by newarts Quote
Such calibrated scales are in the $500's-$5000's range!

I'm thinking that natural targets like the plant leaves mentioned earlier might be good at least for a series of macros at a particular magnification with varying f-number.

I'd likely be best off to quit talking and start doing, just like you said.

Dave
Dave, I went through the same thing myself and decided that there were some things I could quantify, and some things that I just had to wing it with.
Macro resolution fell into the latter category because of just what you found.
So I went out and took pictures instead.
10-27-2010, 05:52 AM   #14
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QuoteOriginally posted by newarts Quote
You people (Lowell and Wheatsfield) are amazing!

You would deny me the pleasure of establishing valid relationships to aid others?

Yet you happily use similar exposure relationships developed by others though theory and experiment?

And your answer to a simple question concerning macro photo magnification limits remains "go take some photos?" Uh, that's no answer at all unless you mean that everyone must discover underlying principles through personal trial and error.



I'm not advocating that individuals in general make measurements "to quantify your gear" - that seems to be what you are recommending; and that is terribly inefficient; rather, I seek to provide some simple guidelines to aid in the process of macro photography to avoid everyone's re-inventing the wheel.

Dave
Dave

Perhaps you misunderstand my comment.

I am not trying to deny you of anything, but simply offering my opinion, based upon experience.

The problem with Macro especially is that you have a ton of competing and conflicting physical constraints.

The two biggest are depth of field and difraction. Difraction is always present, but is generally ignored at wide apertures, since the impact is minimal as a function of the overall lens area. as apertures get smaller the ratio of area impacted by difraction compared to total opening area becomes an ever increasing percentage, which is why sharpness with stopping down has its limits.

BUT.....

you have to trade that off with depth of field, and depending on the three dimensional nature of the subject, it may be more important to have improved depth of field at the expense of ultimate sharpness.

I also suggested that if you want to try some tests, that you use a real life subject, and locate one portion parallel to the densor plane, and the remainder of the subject at differing depths so you can evaluate with your test shots the trade off between depth of field and ultimate sharpness.

However, you will most likely find that there is no hard/quantitative measure you can make with a simple subject, only a qualitative trade off relationship that you can make, and it will be lens specific. And, this measure is already known to a large extent, with the published lens data. they publish sharpness vs aperture data, and DOF is something you can check before you shoot by stopping down.

It is different with the tests I do perform on my lenses, to check metering. I can make a hard measurement in terms of exposure error. It is important to know if a particular lens always over exposes by 1 stop (as an F2.8 zoom with a TC on the K10D) or has exposure drift up linearly as you stop down, as my Tammy 28-75 does from wide open to F32.

So by all means go ahead and test, but in this case, I think you will find that shooting a series of different subjects you will gain more than trying to figure out something from a test target, even a real life one.
10-27-2010, 07:25 AM   #15
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QuoteOriginally posted by Lowell Goudge Quote

Perhaps you misunderstand my comment.
....
The problem with Macro especially is that you have a ton of competing and conflicting physical constraints.

The two biggest are depth of field and difraction. Difraction is always present, but is generally ignored at wide apertures, since the impact is minimal as a function of the overall lens area. as apertures get smaller the ratio of area impacted by difraction compared to total opening area becomes an ever increasing percentage, which is why sharpness with stopping down has its limits.

BUT.....

you have to trade that off with depth of field, and depending on the three dimensional nature of the subject, it may be more important to have improved depth of field at the expense of ultimate sharpness.

I also suggested that if you want to try some tests, that you use a real life subject, and locate one portion parallel to the densor plane, and the remainder of the subject at differing depths so you can evaluate with your test shots the trade off between depth of field and ultimate sharpness.

However, you will most likely find that there is no hard/quantitative measure you can make with a simple subject, only a qualitative trade off relationship that you can make, and it will be lens specific. And, this measure is already known to a large extent, with the published lens data. they publish sharpness vs aperture data, and DOF is something you can check before you shoot by stopping down.....
Thanks for your comments; I understand them well.

I think you ascribe more quantitative goals to my effort than I intend. My intent is simple; it is to be able to say something like,

"Don't worry about diffraction when shooting macros until F-stop x (m+1) is greater than about 24, after that there'll be some sharpness loss."

I'm trying to get some illustrations that show what one might expect.

Dave

PS you say "and it will be lens specific..." Simple theory implies it won't be particularly sensitive to lens specifics for reasonable quality lenses. That's part of what I want to test and illustrate.
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