Observation using my Nikon primes

[Chuck Fishbein]

I did a series of tests with Mike Tapa's adaptor and 12 of my Nikon lenses. Most of them worked brilliantly but I found minor issues at the infinity setting on some of the shorter lenses.

On lenses 50mm and below, the lens went slightly beyond infinity. It was enough to make the shot slightly soft, but not enough for the peaking to change. After re-testing the problem lenses and focusing with a Hoodman rather than trusting the peaking, the lenses gave excellent results, but I could see how this could easily net problems if I was not careful.

I also recorded myself focusing so that I could compare what the peaking suggested was proper and what my eye without peaking determined to be accurate.

I had previously tested all the lenses on charts under studio conditions, but chart tests would not replicate shooting a skyline a half mile away or even 50 foot away.

Perhaps it was just my lenses, Nikon 50mm 1.4, 35mm 2.0, 24mm 2.8. 20mm 2.8. . Some of them are AI vintage and have seen a lot of action, but it would certainly be prudent to do a test of your own under varied conditions (other than a test chart at 10 feet) before you commit them to a gig. .

[Nate Weaver]

Not to post a proper "oh, this is why PL lenses are for pros, blah blah blah", but...

I think stills lenses are designed with the idea that you would always have a high resolution view (optical finder) to focus with. So they get away with details like this, it's never an issue when you can clearly see what's going on when you're shooting.

Modern PL lenses are designed with the idea that an AC has to focus correctly without ever seeing an image, based on measured distances and accurate marks on lens. Usually cine lenses have hard stops at infinity and a properly serviced lens will be correct at that hard stop.

Just a note, I suppose.

[Alister Chapman]

Most lenses focus beyond infinity. This is too allow for temperature variations in the lens, the mount and the camera that could potentially make a lens that focusses at infinity perfectly well on a hot and sunny day not reach infinity on a cold and chilly morning. Even PL's can go a tiny bit past infinity. Small variations in the flange back distance will also change the infinity position. Don't forget the F3 has the ability to alter the flange back if you need to, although this is really there to help get zooms parfocal.

[Chuck Fishbein]

Thanks Alister,
That makes sense. It just takes a little more care to get it right.

@Nate: You're preaching to the choir my friend. And all of what you are saying is spot on when you've got an AC pulling focus for you. I have to admit that that doesn't happen on the majority of my shoots.

[Brian Lai]

Originally Posted by Alister Chapman

Don't forget the F3 has the ability to alter the flange back if you need to, although this is really there to help get zooms parfocal.

Alister, I've noticed the focus scale on my PL Cooke Panchros consistently tape measured 1" closer to focusing through the finder or monitor. This doesn't happen when the same lens is used on an Alexa. Is it time to fool around with the dreaded back focus adjustment?