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Macro Lens Question (entrance pupil)

S

Shelby Lewis

Guest
This isn't MF specific, but I bet I'll end up using an MF lens... so I thought I'd pose it here... and you guys all know your lenses :D

I have an idea for a shot that I'm wanting to do that uses stacked exposures.

The catch... it stacks from macro to infinity. In order to pull this off, you need a lens where the entrance pupil doesn't move. This is usually done with a bellows in conjunction with focusing via camera-body-movement (for/aft)... which means a custom setup. The lens doesn't move at all. But there are a few lens, mostly on compact cameras, where the entrance pupil doesn't change as you focus. I'm wondering if the internal focusing slr lenses are included in this group...

Does anyone know if there is anywhere I can find this info? It's no biggy if I can't, as this is just an experiment I'm wanting to play with for a future concept...

Thanks!
Shelby
 

Jack

Sr. Administrator
Staff member
This is a vast over-simplification, but...

The problem is two-fold: one is entrance pupil moving, two is focal length is actually changing as you focus -- and IMHO problem #2 is far more significant than #1 will be. Change in EP will affect parallax where change in focal-length affects subject magnification. Both/either create ghosting in broad-range focus stacks.

Pure IF lenses in theory do not move entrance pupil, but rather alter focal length directly -- effectively zooming out without altering focus for a net closer focus point. This should eliminate most of issue #1, but will exacerbate issue #2. Also, I'm not convinced that current "IF" macro lenses are 100% IF technology --- IOW I suspect that many use combinations of lens-group extension (albeit internal) and focal length changes to accomplish their focus.

The advantage of fixed lens with bellows focus moving the sensor, is that while altering PoF, you are inversely compensating subject distance (it's measured from the sensor plane). At "normal" shooting distances the inverse compensation is very closely aligned with the rate of subject magnification change curve so the results are generally excellent. However, when you get into macro ranges, the proportionality curves diverge far more rapidly and the result will be less desirable as total focus range captured increases beyond a relatively narrow margin (like a few mm).
 
M

martin54

Guest
This is a vast over-simplification, but...

The problem is two-fold: one is entrance pupil moving, two is focal length is actually changing as you focus -- and IMHO problem #2 is far more significant than #1 will be..........................beyond a relatively narrow margin (like a few mm).

Nice approach Jack, i liked that
 

dougpeterson

Workshop Member
See also: http://www.captureintegration.com/2009/08/25/extreme-macro/

You'll probably need to physically remove any large foreground subjects on your long distance shots so that you have a "clean plate" from which to retouch in the areas which the foreground subjects "bloom" with their out-of-focusness.

Or you can compose the shot so that all foreground elements are frame-bottom, all mid-ground elements are frame-middle, and all background elements are at frame-top so that when the near-ground objects are out of focus you don't have them overlap elements behind them.

Doug Peterson (e-mail Me)
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yaya

Active member
This isn't MF specific, but I bet I'll end up using an MF lens... so I thought I'd pose it here... and you guys all know your lenses :D

I have an idea for a shot that I'm wanting to do that uses stacked exposures.

The catch... it stacks from macro to infinity. In order to pull this off, you need a lens where the entrance pupil doesn't move. This is usually done with a bellows in conjunction with focusing via camera-body-movement (for/aft)... which means a custom setup. The lens doesn't move at all. But there are a few lens, mostly on compact cameras, where the entrance pupil doesn't change as you focus. I'm wondering if the internal focusing slr lenses are included in this group...

Does anyone know if there is anywhere I can find this info? It's no biggy if I can't, as this is just an experiment I'm wanting to play with for a future concept...

Thanks!
Shelby
If your goal is to achieve some sort of infinite DOF and you have an idea of what the final frame/ composition is going to be like, then you can break it into "sections" like Doug has suggested and then you won't be limited to a single lens/ device but you will have to spend some time planing and calculating which lens to use for which section of the image

Sounds like fun, good luck!!!
 
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