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Author Topic: Macro, depth of field and stacking software  (Read 3744 times)

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Offline Federico M

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Macro, depth of field and stacking software
« on: March 01, 2008, 06:47:23 pm »
I'm preparing a short article about the focus stacking software CombineZM used on ancient coins (especially small, but relatively high relief coins). And I would like to know - in particular form people using digital reflex cameras playing a bit with manual focus and other settings - if they think that this software may be useful to them.

Basically, this is a software tool to extended the depth of field, taking more than one shot of a given item and combining the "in focus parts" (avoiding at the same time the problems of diffraction that would arise from reducing the aperture to obtain a similar result).
(See example attached below: I took several shots slowly focusing on a more distant point and then stacked them with CombineZM.)

Just to be sure, this kind of  software is not useful for all ancient coins pictures (and it's almost useless for people using compact digital cameras), but it may be used when you want to do macro photography of very small coins, in particular if they have high reliefs: for instance, for my example here I used a silver 1/12 stater from Miletos (late 6th century B.C.). This coin is both quite small (9.34mm), so that photographing it with 1:1 magnification may be useful, and almost spherical…

I can give other details about the software and the problems it is supposed to solve, but I hope that pictures below will provide a sufficient intuition.

Offline Federico M

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Re: Macro, depth of field and stacking software
« Reply #1 on: March 01, 2008, 06:51:23 pm »
Some additional images, zooming to highlight the problems (with aperture F/4) and the result after stacking several images (about 8, but I likely exaggerated).

Offline slokind

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Re: Macro, depth of field and stacking software
« Reply #2 on: March 01, 2008, 08:27:14 pm »
Oh, my!!!  I wonder what that was invented for.  I'm sure it's expensive.  Pat L.

Offline Federico M

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Re: Macro, depth of field and stacking software
« Reply #3 on: March 02, 2008, 03:16:18 am »
Oh, my!!!  I wonder what that was invented for.  I'm sure it's expensive.  Pat L.

I think it was invented for taking macro pictures, in particular of insects or microorganisms. But it may be useful in general for macro photography of 3D objects (even if - as I already admitted - usually you may obtain sufficiently good results just changing the F parameter of your camera: a lot of info here http://en.wikipedia.org/wiki/Depth_of_field). And potentially also for several other things (I saw really creative uses here and there on the Internet).

The good news is that the software is actually completely free and open source (as open source developers would say, both free as in free beer and free as in free speech!), hence freely modifiable if one is able to do so (which is not my case, unfortunately).
(It's amazing how some people are willing to freely contribute their excellent job to the rest of the world, isn't it? This is another reason for which I like "advertising" a little bit open source projects.)
You may find additional informations here:
- http://en.wikipedia.org/wiki/CombineZM
- http://en.wikipedia.org/wiki/Focus_stacking
The question is more: do you think it may be useful to take coins pictures both for study/research or artistic purposes? If so, I'm going to prepare a detailed explanation (there are already some good ones on the net, but readers here may prefer a tutorial with ancient coins to one with wolf spiders ;)).

This program is also very easy to use - at least at basic level (it's highly customizable to do quite incredible things, in fact) - and I'm going to prepare a step by step tutorial using some ancient coins images... Essentially, you have to load the images (taken slightly changing the focus from one image to the other) and hit run ;D it's really that simple (the software automatically create the depth map that you may see below and composes the pictures, slightly resizing them to compensate for the differences generated by the focusing operations).

In fact, the only expensive things to use it are the camera and lenses, but you already have a Nikon D80 - if I remember correctly - (which is better than the D40x I used to take these pictures) and I suppose you also have macro lenses, hence using these techniques would likely be completely free for you.

Offline Federico M

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Re: Macro, depth of field and stacking software
« Reply #4 on: March 02, 2008, 03:21:43 am »
For people wanting to see the side effects of diffraction, when decreasing aperture to increase depth of field, I attached also a detail of a Roman (? do you think it's authentic?) die taken with aperture F/4 and F/32 (I exaggerated a bit in using extreme aperture values in order to highlight the problems). My explanations may be wrong, so experienced photographers are welcome to correct me :)

As you see in this Roman die, with "optimal" (at least given a few experiments I did and the natural light I had when taking the picture) aperture (F/4) and shutter time, only a very limited proportion of the object may be in focus at very high magnification (the die was almost completely filling the frame).
A relatively fast and easy way increases the DOF is to increase the f-number (reducing the aperture diameter), if your camera allows you do so (as any reflex camera). However, reducing the aperture also reduces the amount of light arriving to your film or sensor, so that the quality of the image and of the colors may not be optimal.
You may try to compensate this using more light to illuminate your subject and/or you may try to process the picture with an image editing tool later on, but it is not always possible to obtain a satisfying result (see the die at F/32) and – in any case – you will loose some details (is it so? Yes, because of diffraction, that is increased when light is passing through a smaller hole. “Diffraction is the name given to the observation that when light squeezes through a small opening it tends to spread out”)

In the big image to the left (F/32) the depth of field is very high, but (as you see in the zoomed image, above part) with created some problems in term of diffraction (which are visible only at high magnification, but still problematic if we want to create a poster of our Roman die!).

Offline moonmoth

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Re: Macro, depth of field and stacking software
« Reply #5 on: March 02, 2008, 04:55:54 am »
There is an example of the effect of diffraction on this page:

https://www.forumancientcoins.com/moonmoth/photo_coins04.html

As for the idea of taking more than one shot and combining the in-focus parts, I do this manually when necessary, which isn't often, and it's not all that difficult.  The result is fine and a lot cheaper than software.  I last used it on this coin, to get the surface of that rusty attachment into focus as well as the surface of the coin.  The software might be useful if you need to do a lot of this, though.
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Offline Federico M

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Re: Macro, depth of field and stacking software
« Reply #6 on: March 02, 2008, 05:18:49 am »
Yes, I saw your pages about coin photography: they are very interesting!

The result is fine and a lot cheaper than software.

From the monetary point of view, it's difficult to be cheaper than 0. This software is free. Moreover, it's really easy to use, so - for people without good editing skills with other software, it may be even easier than learning how to manually combine pictures to obtain a similar result (and it's surely faster).
But I agree, about the fact that one may live happy even without this software :-)

Offline moonmoth

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Re: Macro, depth of field and stacking software
« Reply #7 on: March 02, 2008, 05:41:38 am »
Yes, it could not be cheaper than 0 - sorry about that!  I should really have said that it's usually better for your computer to install only the software you really need.
"... A form of twisted symbolical bedsock ... the true purpose of which, as they realised at first glance, would never (alas) be revealed to mankind."

Offline Federico M

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Re: Macro, depth of field and stacking software
« Reply #8 on: March 02, 2008, 06:27:35 am »
That's true, and yet I would give this a try (looking at the help of the full version), especially if one also has some very small coins with high reliefs (and wants to see them at high magnification) or small artifacts (I agree that for normal denarii or other relatively flat coins - I don't mind any offense to denarii ;) and some have high reliefs - it's not that useful, normally). Or also if one does a lot of macro photography in general.

Installing useless software is not a good idea, I agree. But this is a small and apparently fairly neat program, so it should not change of an inch the performances of a non-prehistoric hardware. After all, also changing the lenses of your camera is not a good practice, in absolute terms, since you may leave small particles enter into it and generate similar problems with humidity or dirt in general... And yet, I guess that you frequently experiment taking pictures with different lenses and settings, even if you don't really "need" to do so (and this creates small "risks" for your camera); the same is valid for software, at least to me (but I admit that I like playing with new software programs in general, and this is not true for everybody).

Federico

Offline Joe Sermarini

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Re: Macro, depth of field and stacking software
« Reply #9 on: March 02, 2008, 06:53:59 am »
Very interesting.  I'm not sure yet what I will use it for, but I expect I will find a use for this software someday. 
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Offline moonmoth

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Re: Macro, depth of field and stacking software
« Reply #10 on: March 02, 2008, 12:46:47 pm »
(...)  After all, also changing the lenses of your camera is not a good practice, in absolute terms, since you may leave small particles enter into it and generate similar problems with humidity or dirt in general... And yet, I guess that you frequently experiment taking pictures with different lenses and settings, even if you don't really "need" to do so (and this creates small "risks" for your camera); the same is valid for software, at least to me (but I admit that I like playing with new software programs in general, and this is not true for everybody).

Federico

In fact the camera I use for coins sits there with its 105mm macro lens in place almost all the time.  But it certainly saw a lot of lens changes when I used to carry it about, sometimes in dusty or dirty conditions, so you are quite right in principle.  I may be a bit more sensitive than usual to software issues because my computer is 3 years old and is starting to behave erratically!
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Re: Macro, depth of field and stacking software
« Reply #11 on: April 03, 2008, 11:09:27 pm »
you did a good job describing and showing the progressively deteriorating effects of using smaller apertures. it's not an easy subject to "get". what you didn't mention is how focal length comes into play. the longer the focal length of the lens (the greater the number preceding the mm) the more depth of field latitude you will have for any given working distance. on a 60mm macro lens at 6-8 inches going below about f10 becomes really tricky on any but the thinnest-reliefed coins if you want all of it to be in focus. use a 200mm lens and you need to back up a couple feet at least but you can use pretty much any aperture and be reasonably sure no matter how thick the coin is it will be perfectly sharp (assuming a good setup).

the problem is that there is a tradeoff. with the shorter focal length lenses you get the close-in, comfortable working distances at the sacrifice of the above-mentioned depth of field constraints. with longer focal length lenses you get idiot-proofing at the cost of an awkward working environment - not to mention the additional expense; a 200mm macro will likely cost over a thousand dollars!

it should also be noted that the sharpest aperture for almost any lens will fall between f/5.6 and f/8.

ras

Offline moonmoth

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Re: Macro, depth of field and stacking software
« Reply #12 on: April 04, 2008, 02:04:47 am »
You are right about the focal length, and I didn't cover choice of lens.  But maybe it's worth adding a paragraph.  I think that around 100mm is the best compromise between depth of field, usability and magnification, as well as being (as you say) a lot more affordable than longer focal lengths.   And the last time I looked, some of the the shorter lenses did not give 1:1 magnification, and the longer lenses were less sharp (though this might have changed since).

I found experimentally that f11 gives me the best results. Ancient coins are often far from flat as well as hard to position at exactly 90 degrees to the lens, and some depth of field is essential.  It is quite possible that I might say something different if I were working on modern coins.

Bill
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