Infinity Focus is not quite right

[gorbas]

Try something further away. One common definition of "infinity" for photographic pursposes is 1000x - 1500x the focal length of the lens.

Can you please point me to source of this info?

 

[MattKing]

...means that the problem you are having is not within any lens, but the issue of focus 'mismatch' (between the viewfinder and the focal plane)

Except that @mehguy has not yet determined if this exists. As far as I can tell, he hasn't encountered any issue with out of focus photos.
He has simply noted a small discrepancy between the markings on the lenses, and his estimate of distances, when the viewfinder indicates the subject is in focus.

 

[Craig]

Except that @mehguy has not yet determined if this exists. As far as I can tell, he hasn't encountered any issue with out of focus photos.

Yes, as far as we know the camera might be functioning perfectly. The viewfinder focus aids might be perfectly calibrated to render an in-focus image on the film when the viewfinder says the image is in focus. We have no confirmation if this is true or not.

 

[ic-racer]

Thank you very much IC-Racer! Very tempting!

One can also search for GOKOSHA on EBAY.

 

[wiltw]

Can you please point me to source of this info?

Here is one of the few references that quantify Infinity in any terms beyond an informal 'across the fence' description...

How to test image quality with a camera that is focused to infinity?

I have to test a camera that is focused to infinity, but I cannot take an image of an object that is more then 1.5 meters away from the camera because I can't get it out of the room itself. (The ro...

photo.stackexchange.com

Someone who was (still is???) affiliated with Northwestern University wrote this response:

"Leonard Evens​

22-Aug-2008, 18:10​

"Infinity" for photographic lenses is 1500 X the focal length.

It's always nice to have a definite number, but how many of us are going to calculate 1500 x the focal length in units we are familiar with, and then measure out that distance in the scene. Also, as I tried to explain above, there is no one distance which is effectively `at infinity'. It all depends on close you have to be to the focal plane before you can no longer tell the difference. That in turn depends on the focal length and how closely you look as well a what you are trying to accomplish.

Let me give a simple method which anyone can use without making distance measurements. This would apply when you really do want to focus `at infinity' rather than just having infinity adequately in focus, in which case you would use the hyperfocal distance.

Focus on two or three very distant points. See if there is any focus spread on the rail among them. If within the accuracy that you can focus they are all at the same place, then you are focused for all practical purposes at infinity. You won't do better than this by measuring out 1500 X the focal length or 750 X the focal length or 3000 X the focal length or whatever.​

...as part of this thread. https://www.largeformatphotography.... infinity,are usually marked at about 60 feet.

 

[BrianShaw]

That was a good thread; I forgot about it. It’s a traditional rule of thumb based on physics and circles of confusion. The reason isn’t not a precise number is because there are many variables some based in psychophysics, hence statistical and inherently include variability. While one could probably reverse-engineer the rule o’thumb it’s probably best to accept that it gives a result far enough away where any farther is irrelevant from a practical perspective but closer could be problematic. “Pick a number, any number: 1000, 1500, 3000: It depends…”

 

[gorbas]

Thank you! So for 1500X and 50mm lens that is 75 meters.
It's more to do with what you can see from your home and what is around you at 75 meters distance and further.

 

[ic-racer]

In the case of Nikon F or Nikkormat, how would you do this? Mirror angle adjustment is straightforward, but I don't recall seeing any shims used where lens mount meets mirror box casting, or where mirror box bolts onto main body casting. And those mirror box castings are pretty stout, and do not seem designed for bend-to-adjust alignments.

Clip from the "F" service manual. In addition to using a dial indicator, one can also use a "standard" lens that is correctly set to infinity and read the flange-focal length error off the autocollimator scale.