[sbc]

I had the SFXn, Z-1 and Z-1p. They were long gone before I learned about AF calibration starting with the K-20D.
I am wondering if anyone sacrificed a roll or two of film to test the AF for front/back focus?
Maybe some of my old lenses were not really soft at all.

[UncleVanya]

I had the SFXn, Z-1 and Z-1p. They were long gone before I learned about AF calibration starting with the K-20D.
I am wondering if anyone sacrificed a roll or two of film to test the AF for front/back focus?
Maybe some of my old lenses were not really soft at all.

Sure it is possible, though it was only as digital systems resolution increased that the very small calibration distance errors became noticed. I would expect that only with very thin depth of field and very high resolution film would the tiny differences in tolerance that modern high resolution digital sensors can detect show up.

[zapp]

Some people did that, some even calibrated their bran to decide focus differences for different f-stops. You would not sacrifice a roll of film, but several rolls and keep practicing your skills.
We’re your lenses not soft at all. Maybe, but modern sensors are more demanding and modern glass is ‘less soft”, aberration wise modern glass has much improved.

[Bob 256]

Film had a tendency to warp and not lay completely flat over the exposure area so there were sometime issues with uneven focus which came up. I think it was easier to use a smaller f-stop and not worry about exact focus than to go through a lot of film to calibrate a focus offset for each lens which might vary from roll to roll due to film warpage anyway. Of course, if it was suspected that there were focus errors due to a camera issue, the camera itself would be subjected to repairs using a ground glass in place of film to check critical focus at the center of the film aperture. Nowadays, the output of the sensor can be viewed directly which guarantees critical focus so it can place higher demands on that process and allow better fine adjustment of the critical focus. UncleVanya alluded to this and digital systems can also allow focus offsets to be paired with X number of lenses so these offsets are automatically applied when a given lens is attached. For film, you'd just have to remember or write down that info.

[TwoUptons]

I remember hearing about people using the ground glass trick to calibrate high end cameras in the 90s, but I never knew anyone who had actually done it...
I always wondered how you knew the ground glass was in exactly the right place... there would have been some play in where the film ended up, too...

I don't remember ever having front/back focus issues with my PZ-20. Of course I had occasional focus issues (in-between the couple?! stupid single-point focus)
I was far more likely to have camera shake issues, or subject movement issues, or just "what was I thinking?" issues... that got me blurry photos.

It's actually really annoying to go back to some of my slides and negs that I remember as being awesome, scanning them in, and going, "eew..." because I'm pixel-peeping 30-year-old film...
And I did some of my father's slides, which looked great on the living room wall as a child, and they're even worse (his Rollei may have been good, but that Vivitar zoom, not so much...)

-Eric

[stevebrot]

I am wondering if anyone sacrificed a roll or two of film to test the AF for front/back focus?

Probably not. There was no way to apply a correction. It was not unusual for people to check the viewfinder accuracy, however. That is done be putting a ground glass or focus screen across the film gate.


Steve

[Bob 256]

I remember hearing about people using the ground glass trick to calibrate high end cameras in the 90s, but I never knew anyone who had actually done it...
I always wondered how you knew the ground glass was in exactly the right place... there would have been some play in where the film ended up, too...

-Eric

I've done it a few times. It requires a fine ground glass of the appropriate size which sits on the film rails. As long as it's using the rails as a reference, it should be at the film focusing plane (ignoring any 'curl" the film might have). You also need a magnifier to enlarge the GG view for critical focus. The main use for this is to check the viewfinder and verify the AF is working as it should. The PZ-1p would allow operation with the rear open so this was a practical calibration check using bulb to keep the shutter open (with a given test lens in place). I've seen it done with a video camera (shooting the ground glass) so the magnified image shows on a television monitor but that's totally unnecessary in most cases.

[Michail_P]

Fine tuning in analog? Maybe I would if no digital cameras were available. Now I cannot see why this would matter to me. I wouldn’t sacrifice film for calibration now.

[aaacb]

Happy times before pixel peeping and high res sensors gave us 1kg 50mm primes I think it was a matter of not being able to confirm in the field that, shot wide open, AF fine tuning was the issue (because of no instant view, and why waste film for minute differences), stopped down it's not a problem except for gross inaccuracy which requires servicing?