Rail Focus or Lens Focus

Just bought that first macro lens? Post here to get helpful feedback and answers to any questions you might have.

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cbphoto
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Rail Focus or Lens Focus

Post by cbphoto »

Greetings all,

First post here. Great work all around!

Question:
When should one use a rail to focus on an object/scene, and when should someone use the lens to focus on an object/scene?

After some web research, it seems that true macro work (1:1 and closer) needs to use a rail system such as the Cognisys StackShot. And when one is shooting a scene such as a room (camera-to-subject distance ≥ 2 meters to 10 meters) lens focusing should be done. Is my assumption correct?

At what enlargement ratio does the use of a rail system become valuable? 1:1? or maybe 1:5?

Any info is appreciated.
~ CB

rjlittlefield
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Re: Rail Focus or Lens Focus

Post by rjlittlefield »

For starters, see the article at https://zerenesystems.com/cms/stacker/docs/troubleshooting/ringversusrail .

Then feel free to discuss further here. I wrote that article, so I'll be happy to expand or clarify as needed.

--Rik

cbphoto
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Re: Rail Focus or Lens Focus

Post by cbphoto »

Thanks!
~ CB

blekenbleu
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Re: Rail Focus or Lens Focus

Post by blekenbleu »

rjlittlefield wrote:
Wed May 25, 2022 11:32 am
For starters, see the article at https://zerenesystems.com/cms/stacker/docs/troubleshooting/ringversusrail .
In that table, what is meant by bellows front vs rear?

Some lenses, e.g. my Canon EF 50mm f/1.4, change focus by moving their front element in and out,
while others do not. When changing focus by ring, should one be preferred over the other,
or is minimizing focus "breathing" (change in magnification) more important?
Metaphot, Optiphot 1, 66; AO 10, 120, and EPIStar 2571
https://blekenbleu.github.io/microscope

rjlittlefield
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Re: Rail Focus or Lens Focus

Post by rjlittlefield »

blekenbleu wrote:
Mon May 30, 2022 12:04 pm
rjlittlefield wrote:
Wed May 25, 2022 11:32 am
For starters, see the article at https://zerenesystems.com/cms/stacker/docs/troubleshooting/ringversusrail .
In that table, what is meant by bellows front vs rear?
"Bellows front" means to move the front standard on which the lens is mounted, while keeping the camera in a fixed location.
"Bellows rear" means to move the rear standard on which the camera is mounted, while keeping the lens in a fixed location.
Some lenses, e.g. my Canon EF 50mm f/1.4, change focus by moving their front element in and out,
while others do not. When changing focus by ring, should one be preferred over the other,
or is minimizing focus "breathing" (change in magnification) more important?
In general, the troublesome differences in perspective are caused by movement of the entrance pupil. Simple changes in magnification, without movement of the entrance pupil, can be compensated in the stacking software. That's why "bellows rear" is so good -- it introduces a lot of change in magnification, but the entrance pupil does not move at all.

In the few lenses that I have studied, internal focus lenses have had less perspective change than lenses that extend. But I do not know of any reason why that should be true for all lenses, so for this question I think the bottom line has to be "I don't know. You'll have to try it and see."

--Rik

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