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Archive 2014 · understanding rangefinder focus shift

  
 
fstopperdown
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p.1 #1 · p.1 #1 · understanding rangefinder focus shift


I'm not sure if I'm seeing focus shift or just softness at minimum focus distance.

It is soft on the left third of my test shots but it's not terrible at f/1.4 and sharpens by F/2.8 and is great at F/4 and beyond.

How much focus shift is acceptable?

Is it gone by F/4 or just masked by the DOF?

I don't forsee shooting at minimum distances.

Most likely shooting at 7-15 feet and beyond for some of my bar bands, news/PJ assignments.

Also, I do long exposure landscapes typically at F/8 to F/16.

FWIW... I'm using it on a Leica M2 as a starter set to see how much I want to invest in Leica.

Any help appreciated.

I can return the lens no issues.




May 18, 2014 at 11:21 AM
EB-1
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p.1 #2 · p.1 #2 · understanding rangefinder focus shift


I don't believe that any decent lens should be softer on one side than the the other. Usually I rotate the camera around the lens axis and check for sharpness. The upside down image should be the same as the rightside up image.

You might want to post in the Alternative Gear forum.

EBH



May 18, 2014 at 11:31 AM
Gochugogi
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p.1 #3 · p.1 #3 · understanding rangefinder focus shift


Being soft on one side isn't focus shift. Your lens is decentered and needs to go to the shop for alignment. It would need to be a really good deal to offset repair costs.


May 18, 2014 at 04:46 PM
Monito
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p.1 #4 · p.1 #4 · understanding rangefinder focus shift


Gochugogi has it right.

Focus shift is what happens when the lens stops down during the taking of the photo. With a very few lenses, when the lens is focused wide open, the plane of focus will shift when it gets stopped down to f/4 say. It "goes away" by f/8 and beyond whether or not it has de-shifted or is still shifting; at those f/stops the depth of field is large enough to mask a focus shift effect.

Focus shift moves the scene plane of focus forward or back while maintaining the same orientation to the optical axis, i.e. perpendicular. The plane of focus does not tilt.



May 18, 2014 at 05:01 PM
fstopperdown
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p.1 #5 · p.1 #5 · understanding rangefinder focus shift


Thank you!

That was very helpful.



May 18, 2014 at 06:09 PM
Alan321
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p.1 #6 · p.1 #6 · understanding rangefinder focus shift


If it is soft on all sides in a ring around the centre then it is probably curvature of focus, which is a lens design issue. Only DOF will fix that. However, it is far more obvious when photographing flat target sheets than it is in real life where the subjects are more 3D and it doesn't too much which part is in focus.

Leica is way too expensive to be getting a de-centred lens element. Either exchange it or give up on it completely, but don't go through the hassle and delay of getting it sent away and fixed.

- Alan



May 22, 2014 at 11:16 AM





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