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Focusing rails

Victor Oyarzun , May 16, 2011; 04:55 p.m.

I am thinking on getting a focusing rail for focus stacking macro photos but, not sure how it would work for this purpose as if I move the rail (position of the camera) not the actual focus it would change the frame slightly. Would this change affect the stacking of the photos lately in CS5? How far I could go, distance wise?

Responses

Joseph Wisniewski , May 16, 2011; 05:18 p.m.

Yes. It would affect the stacking greatly in CS5. The change in perspective with each change in focus produces strange looking boarders on edges of objects. This is called by several names, like "fringing" or "ringing". CS5 does not handle it well, some other stackers, like CombineZ, Helicon Focus, or Zerene Stacker, do a lot better.

The longer the lens you use on the rail, the less fringing you'll get. If you have a 200mm, you'll end up with a 10:1 subject-size to perspective point distance, and minimal fringing. An "infinite perspective" lens totally eliminates fringing, but telecentric macro lenses are insanely expensive. There's a technique for coupling two lenses with a telecentric stop between them that's surprisingly cheap and easy.

Or switch to a bellows, and use "bellows draw" (rear standard movement) for your focus stack. That gives you a finite (and very short, if you want) perspective, which might look more natural for many subjects than the "infinite" perspective and total "flattening" you get from the use of long lenses or telecentric photography.

Victor Oyarzun , May 16, 2011; 07:19 p.m.

Thanks Joseph, I am glad I asked because the rails and the software probably it would be too much for me, just an enthusiast.
Regards

Geoff Mower , May 17, 2011; 03:02 a.m.

Thanks Joseph, I am glad I asked because the rails and the software probably it would be too much for me, just an enthusiast.


Victor, in case you meant "too expensive", you should know that the the CombineZM software mentioned by Joseph is a free download, and well worth trying.

Victor Oyarzun , May 17, 2011; 09:03 a.m.

Oh! Yes, thats' what I ment, becasue I understand the Helicon Focus is expensive. Thanks Geoff, I will give it a try.
Regards.

Derek Thornton , May 19, 2011; 07:53 p.m.

I have never tried stacking photos, so correct me if I am wrong. What you are trying to achieve is a closeup with great DOF, right. So would it be best to not move the camera but move the point of focus? Say you are shooting a spider head on and want the front legs in focus as well as the eyes. Fix camera to tripod and do not move. Focus on legs, shoot. Focus on knees, shoot. Focus on eyes, shoot. Then take three photos and combine. If you use a rail that will move whole camera. If you move the camera, how will the software line every thing up?

Joseph Wisniewski , May 24, 2011; 12:36 p.m.

Derek, there will typically be an even greater shift in the "perspective point" if you try refocusing the lens. As you focus, the bulk of the lens moves away from the camera, and that includes the lens's aperture, the "entrance pupil" that is what determines the angle of view.

There's also the issue that many lenses do not have sufficient "fine control" on their focusing collars to do what you describe, focusing on many different planes of the subject.

There are advanced techniques to get around these things. The use of a "telecentric stop" on a macro lens, or the use of "bellows draw" focusing (which requires a bellows with a moveable rear standard, obviously).

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