Premium Member Paul Bruening Posted January 12, 2010 Premium Member Share Posted January 12, 2010 When you measure for critical focus do you measure from the film plane or from the outermost element of the lens? Link to comment Share on other sites More sharing options...
Mike Panczenko Posted January 12, 2010 Share Posted January 12, 2010 When you measure for critical focus do you measure from the film plane or from the outermost element of the lens? In 35/16mm you would measure from the focal plane. In B4 style ENG video mounts- but not all the cine style mounts!!!- you would measure from the front element, or the green marking on the lens barrel. Link to comment Share on other sites More sharing options...
Premium Member Paul Bruening Posted January 12, 2010 Author Premium Member Share Posted January 12, 2010 In 35/16mm you would measure from the focal plane. In B4 style ENG video mounts- but not all the cine style mounts!!!- you would measure from the front element, or the green marking on the lens barrel. Thanks, Mike. I just shimmed my Fries 35R3's lens board. The critical focus is perfectly on the money when measured from the film plane. I just had to make sure I wasn't goofing the reference point up. Link to comment Share on other sites More sharing options...
Premium Member Chris Keth Posted January 12, 2010 Premium Member Share Posted January 12, 2010 Thanks, Mike. I just shimmed my Fries 35R3's lens board. The critical focus is perfectly on the money when measured from the film plane. I just had to make sure I wasn't goofing the reference point up. Sounds like you're all good. I've never measured focus from anywhere but the film plane. ENG lenses, as Mike noted, are measured from the end of the lens but I've never even thought about measuring focus with one of those. Link to comment Share on other sites More sharing options...
Premium Member Paul Bruening Posted January 12, 2010 Author Premium Member Share Posted January 12, 2010 Sounds like you're all good. I've never measured focus from anywhere but the film plane. ENG lenses, as Mike noted, are measured from the end of the lens but I've never even thought about measuring focus with one of those. Thanks, Chris, I'll check infinity on all my lenses tomorrow when there's daylight. I'm going to go ahead and shoot a test roll for critical focus while I'm at it. Link to comment Share on other sites More sharing options...
Tom Jensen Posted January 12, 2010 Share Posted January 12, 2010 In film you always measure from the plane but when you want critical focus you eyeball it on lenses 50mm and longer. If it's sharp to the eye, it's sharp on film. Non film, I have no idea. Link to comment Share on other sites More sharing options...
Premium Member John Sprung Posted January 12, 2010 Premium Member Share Posted January 12, 2010 ...when you want critical focus you eyeball it on lenses 50mm and longer. If it's sharp to the eye, it's sharp on film. That works provided that the ground glass is correctly seated and the mirror shutter is in the right plane. That's almost always the case, but it's one of the things you test when you check out your package. Shoot diagonal newspaper tests to see exactly what's happening. -- J.S. Link to comment Share on other sites More sharing options...
Premium Member Paul Bruening Posted January 12, 2010 Author Premium Member Share Posted January 12, 2010 Darn! All the lenses over-focus. They go beyond infinity. At the infinity, end setting on the focus ring the image blurs quite a bit. Backing the ring towards the other end sharpens up infinity. Do I have too much FFD or too little? Link to comment Share on other sites More sharing options...
Premium Member John Sprung Posted January 13, 2010 Premium Member Share Posted January 13, 2010 A lot of lenses do that. It's a good thing, that way you can roll thru critical focus at infinity. Otherwise, you'd be depending on the accuracy with which the hard stop was set. If it was set a little short, you'd be SOL. -- J.S. Link to comment Share on other sites More sharing options...
Premium Member Paul Bruening Posted January 13, 2010 Author Premium Member Share Posted January 13, 2010 A lot of lenses do that. It's a good thing, that way you can roll thru critical focus at infinity. Otherwise, you'd be depending on the accuracy with which the hard stop was set. If it was set a little short, you'd be SOL. -- J.S. Tim said pretty much the same thing, especially about Nikon lenses. He called it, "Overstroking." I've checked and all of these Nikons overstroke. All ten of them. Matt Duclos collimated them all when he put the focus gears on them. I'm going to assume they're all set-up correctly. Link to comment Share on other sites More sharing options...
Premium Member Chris Keth Posted January 13, 2010 Premium Member Share Posted January 13, 2010 Tim said pretty much the same thing, especially about Nikon lenses. He called it, "Overstroking." I've checked and all of these Nikons overstroke. All ten of them.Matt Duclos collimated them all when he put the focus gears on them. I'm going to assume they're all set-up correctly. It's also a good way to tell a green focus puller from a good one. The ones who are overstepping their experience will almost always assume infinity is where the barrel stops. Link to comment Share on other sites More sharing options...
Jonathan Bowerbank Posted January 28, 2010 Share Posted January 28, 2010 Shooting ENG, just zoom in real quick and get critical focus by eye ;) Link to comment Share on other sites More sharing options...
James Martin Posted February 1, 2010 Share Posted February 1, 2010 Regarding overstroking - I have been told that putting a significant amount of glass filters *CAN* (though not experienced myself) alter the focus slightly, hence the need to go beyond infinity. In my experience many cheaper lenses (including the RED zooms) are not even marked up at infinity right - I often found it to be sharpest a hair short. For HDTV/B4 lenses, the general rule I have been taught is if the lens has a green ring around it (eg. Canon, Fuji), then that is what the scale on the lens is reading from. If it does not (Panavision Digital Primos, I assume Zeiss Digiprimes) then you go from focal plane. Hope that clears some things up, but if I'm wrong let me know! Link to comment Share on other sites More sharing options...
Premium Member John Sprung Posted February 1, 2010 Premium Member Share Posted February 1, 2010 Another thing you can try: Set the camera up locked off and focused by eye on something very near its close limit. Stretch your tape the other way around, with the dumb end on the subject, and see whether the focal plane or the front element lands closest to what the ring says. -- J.S. Link to comment Share on other sites More sharing options...
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