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Focal length change from close to infinity and how that affects...

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sanfairyanne:
I believe I'm right in camera lenses do not hold exact focal length throughout their range from close to infinity. If this is correct does it affect focus stacking. If so how do photographers correct for this?

Many thanks in advance.

BobShaw:
Yes and yes. Each image is a different magnification so ideally avoid it with a good lens and small aperture but most software like Photoshop or Helicon are pretty good at fixing.

sanfairyanne:

--- Quote from: BobShaw on April 22, 2022, 07:06:06 pm ---Yes and yes. Each image is a different magnification so ideally avoid it with a good lens and small aperture but most software like Photoshop or Helicon are pretty good at fixing.

--- End quote ---
Thanks Bob, from my experiences Helicon and Zerene Stacker have been ok, but rarely perfect. I've learnt how to improve a Photoshop stack using layers by brushing in imperfections, then stamping the layer.  I've yet to see a tutorial for focus stacking that actually explains the different magnifications from close focus to infinity. As you say a small aperture would help but who wants to shoot at f16, that sort of defeats the purpose. Personally I wonder why no lens manufacturer has developed a slow lens i.e. one where the widest aperture was for example f8 or even f11. Imagine having a lens where the sharpest f stop was f16. One would assume the lens would also be much lighter. It's for this reason I'm happy with the kit f4 lenses on my Z7.

PeterAit:
This is one reason that most folks seem to prefer moving the camera rather than changing the focus.

kers:

--- Quote from: sanfairyanne on April 23, 2022, 01:56:13 am ---... As you say a small aperture would help but who wants to shoot at f16, that sort of defeats the purpose. Personally I wonder why no lens manufacturer has developed a slow lens i.e. one where the widest aperture was for example f8 or even f11. Imagine having a lens where the sharpest f stop was f16. One would assume the lens would also be much lighter. It's for this reason I'm happy with the kit f4 lenses on my Z7.

--- End quote ---

f16 will always be less sharp than f8, independent of type of lens, because of the physical effect of diffraction.
some explantion here: https://photographylife.com/what-is-diffraction-in-photography.

btw; The interest in making slow lenses has grown lately due to the stabilisation built into camera's.

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