Move focus ring or camera, when taking stacks?

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Move focus ring or camera, when taking stacks?

Post by Marcel »


I'm trying to get into macrophotography, the camera (Canon D40) and lens (EF 100mm) I already own. My question is about focus stacking:

This morning I saw some 'youtubes' about the StackShot from Cognisys. Looks very nice to me because it solves my first question about photomacrography: how to get equidistant focuslayers (it IS important, is it?).

However, in my understanding, the different focus planes should be set by moving the focus ring of my lens and not by moving the whole camera towards the object because then the object will appear bigger and bigger on the camera's sensor. Looking at the results on some sites, this method cannot be so wrong after all, but I still don't understand why it works.

Does it mean that the stacking software (zerene/photoshop whatever) compensates for this "change of perspective"?

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Post by lauriek »

Yep the software should take this into account. Certainly Zerene does.

One thing to watch out for - either start off at the back, or check your back/front framing before starting and ensure you have a bit of space on the tightest shots, as those may be cropped slightly to compensate for the framing change..

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Post by Chris S. »

Marcel, welcome to the community! :D

One of the FAQs available on the Zerene Systems' Website addresses your question very well, and I'd recommend it strongly: Is it better to use a focus rail or the ring on my lens? The FAQ, as well as Zerene Stacker software, was written by Rik Littlefield, who is an administrator here.

Yes, getting "equidistant focus layers" is fairly important in most situations encountered by macro photographers. There are cases where it doesn't matter so much, but listing them at this point would probably just cause confusion.

The Cognisys StackShot you mentioned is a very nice piece of kit, incidentally, and very fairly priced for the utility one gets from it.

By the way, this thread would probably fit better in the "Beginners' Macro" forum, and I'll move it there after you've had a chance to see this message.


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Post by rjlittlefield »

Marcel, hello, welcome aboard! I'm the fellow that Chris S. mentions.

I'm still trying to figure out how best to explain the issues that you're asking about.

It's really easy for a beginner to get started thinking that there must be one "right" method and all the others are "wrong". That's a trap. In fact almost every method you would seriously think about using is not perfect but will work pretty well. The reasons are that a) focus stacking software is very good at correcting for scale changes, and b) most shooting methods do not cause a troublesome amount of perspective change.

There are a few shooting methods that seem natural and attractive, but in fact will not work very well. One example is trying to focus stack a necklace on a modeling stand, with a wide angle lens, by moving the camera on a focus rail. That fails because the amount of perspective change is too large, the same problem illustrated in the writeup using a flower and jar.

It was seeing people try a few of those methods, get bad results, and not understand why, that prompted me to write that page Chris S. references.


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Post by Marcel »

Thank you for your answers. They made things clear to me.
In one sentence: yes, stacking software DOES compensate for changes in perspective and scale, but only within certain limits: stacking software will not turn a fish-eye into a macro-lens because it distorts too much.

Oh, and the article "Is it better to use a focus rail or the ring on my lens?" is really great: it compresses my four days of "googling" in 1 article ... if only I'd found you earlier.


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Post by EyeDontKnow »

Think about the big picture.....
Moving the focus ring does change the depth-of-field and other attributes, in that the internal lens elements change while doing-so.
Moving the subject often changes the lighting (by a small amount, depends).
Moving the camera body, changes none of either. (ok, it does, but to a lesser degree.)

I move the camera body....forward or aft, usually.
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