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back focus working with 16mm lenses


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#1 oscar jimenez

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Posted 12 March 2009 - 06:13 PM

Hi everyone,
I was trying a regular 16mm zoom lens Zeiss 10-100 to be able to work at 2k without sacrificing lens field of view like with 35mm lenses at 2k, I wanted to skip working with 35 lenses and work all the way at 2k for tv commercials with 16mm lenses, this lens is a Bayo mount lens and I tried a Angenieux bayo zoom as well, and a 9.5mm lens as well, thing is that zoom lenses didnt held focus consistently all the way tru the focal lengths and the wide angle seemed that the focus was at the front element, so I saw sharp in focus all the imperfections of the element, and everything else out of focus. I was able to do focus at fixed focal lenghts within the zooms but when closing the lense and focusing, then wide up again, image was soft. funny that using 35mm lenses this has not happened to me, please, anyone with similar issues, any clues would be very much appreciated.
best
oscar
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#2 John Sprung

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Posted 12 March 2009 - 08:19 PM

Most likely you need to send that zoom out for calibration. If back focus is correct with all your other glass, then that zoom is the problem. If you're using it with an adapter, that could be the problem.




-- J.S.
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#3 Matthew Rogers

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Posted 12 March 2009 - 10:15 PM

Hi everyone,
I was trying a regular 16mm zoom lens Zeiss 10-100 to be able to work at 2k without sacrificing lens field of view like with 35mm lenses at 2k, I wanted to skip working with 35 lenses and work all the way at 2k for tv commercials with 16mm lenses, this lens is a Bayo mount lens and I tried a Angenieux bayo zoom as well, and a 9.5mm lens as well, thing is that zoom lenses didnt held focus consistently all the way tru the focal lengths and the wide angle seemed that the focus was at the front element, so I saw sharp in focus all the imperfections of the element, and everything else out of focus. I was able to do focus at fixed focal lenghts within the zooms but when closing the lense and focusing, then wide up again, image was soft. funny that using 35mm lenses this has not happened to me, please, anyone with similar issues, any clues would be very much appreciated.


Hey Oscar, is there any particular reason you only want to shoot in 2k? You do know that you will see more noise in your footage and it won't be as sharp, right? Why not just use 35mm lenses and shoot at 4k? It's really not overkill even for SD commercials-you can see a difference between the 4k and 2k.

Matthew
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#4 Nigel Smith

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Posted 18 March 2009 - 07:06 AM

Hey Oscar, is there any particular reason you only want to shoot in 2k? You do know that you will see more noise in your footage and it won't be as sharp, right? Why not just use 35mm lenses and shoot at 4k? It's really not overkill even for SD commercials-you can see a difference between the 4k and 2k.

Matthew

Hi Matthew
I was planning to purchase a RED ONE to work with our lenses and accessories from an ARRI S16mm SR2.
I have Zeiss High speed 9.5, 12, 16 & 25mm primes, a Canon 8-64mm zoom, Canon 150mm [with doubler], Kinoptik 5.7mm wide, and Zoomar 90mm macro. All use PL mount adapters.
Do you think I will have issues with back focus?
I'm also slightly worried by the suggestion of noise and soft images at this resolution. :(

Edited by Nigel Smith, 18 March 2009 - 07:07 AM.

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#5 John Sprung

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Posted 18 March 2009 - 10:46 AM

Hi Matthew
I was planning to purchase a RED ONE to work with our lenses and accessories from an ARRI S16mm SR2.
.... Do you think I will have issues with back focus?
I'm also slightly worried by the suggestion of noise and soft images at this resolution. :(


With those lenses, you'll be pretty much stuck in 2K mode. If you get lucky some of the longer ones may cover 3K, but you'd have to test. Remember that Red's version of 2K -- or any K -- means Bayer masked photosites, not pixels. Bayer gives you one color per location, not three. So, the resolution you get in Red 2K mode is substantially less than ordinary HDTV. Back focus could also be a problem, but a solvable one. Buying glass designed for 35mm is the only sure way to escape the 2K resolution limit.




-- J.S.
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