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July 15th, 2006, 06:46 PM | #16 |
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I am assuming this does not apply to the manual lens in any way since it has a physical flangeback adjustment. Right?
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July 15th, 2006, 07:00 PM | #17 |
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It has always driven me crazy that you have to adjust for back focus with video cameras.. you don't have to with film cameras.. but, because I've been "warned" I do it regularly and with precision...
To tell the truth, I've never tried just putting the lens back on the camera, as I would do with my 16mm camera (for which I have 7 zoom lenses and 5 primes)... Could someone explain what changes when you remove and then re-mount a lens on a video camera? |
July 16th, 2006, 06:29 PM | #18 | |
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Best, Christopher |
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July 17th, 2006, 09:32 AM | #19 |
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I'm not sure I understand your response, Christopher -
Let me just say, rather than argue "abstract concepts", that I personally bought my first 16mm camera, a Bolex, in 1962 not far from where you are - Los Altos Rancho Camera Shop - I bought it off the shelf with an early Pan-Cinor zoom. By 1973 I had owned 3 other Bolexes and an Arri 16s and and Arri II (35mm). For example, I shot a feature length documentary (ACAPULCO GOLD) during that time with a 400' Bolex and an Angenieux 12-120 and a Switar 10mm - it was blown up to 35 and distributed nationally - and it's currently available on DVD (although I don't get a dime from it). During the 70's I owned a super16 Eclair NPR, an Eclair Camerette and a CP16. During the 80s I owned a total of five Eclair ACLs (one super16) and in 1990 bought a used super16 Aaton LTR7, which I still own. As a result, I have owned nearly 20 zoom lenses made by Angeniux, Cooke, Century Optics, Zeis and Canon, as well as numerous primes. Except for having the back focus CHECKED (just to be sure) when buying a new lens, I have never had any camera or lens ADJUSTED for back focus - You buy them, put them on, and shoot... That has been my experience.. So, what I'm asking is, simple question that has never been answered to my satisfaction - "why do they advise that you redo backfocus adjustment every time you change a lens on a video camera? - what changes?" I do it because I'm careful, and because it says to do it, but "why?" |
July 17th, 2006, 10:20 AM | #20 | |
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July 17th, 2006, 10:21 AM | #21 | |
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The only point I was making is how nice it is that you can do this calibration yourself with the XL H1. Best, Christopher |
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July 18th, 2006, 05:25 AM | #22 |
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::edit::: clicked on dpreview and realized by digicam's christopher was talking about digital still camera's not digibeta cameras (which also go in for lens matching) so my post was a waste of space....
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July 18th, 2006, 06:27 PM | #23 |
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Please understand, my comment was meant as a general question about video cameras, not a comment on the H1 itself.. the flange back memory function is a terrific tool..
Also, yes I always check a 16mm lens when I buy it, but I only check it when I buy it, not every time I remove then replace the lens... And I've never had to have one modified or adjusted, even wide angle zooms, because I always buy lenses that are in pristine condition, or new ... It just suddenly struck me as curious that I have always accepted (and, I admit, recommended, as on this forum) doing it on video cameras - but I have never questioned why, that's all... My guess is that it needs to be done because the lenses ARE adjustable, and therefore can inadvertably be changed... but I just don't get why they have to be adjustable in the first place with modern non-tube cameras.. |
July 18th, 2006, 07:11 PM | #24 | |
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Best, Christopher |
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July 19th, 2006, 07:10 AM | #25 |
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Hi, I'm just curious, what is actually changed and how when the back focus of the XL H1 is changed? (I know Hasselblad adjusted the length of their still camera bodys with a big hammer (!) if the body was too long. First they replaced the lens with a metal cylinder. Then they adjusted the length by banging with the hammer until the length was correct!)
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July 19th, 2006, 07:54 AM | #26 |
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Christopher: Every manual I've ever read recommends readjusting back focus every time you remove or change a lens on a video camera... And, as I said, I do it because I'm careful, and recommend the same procedure to others... Better safe than sorry, but still, seems unnecessary somehow...
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July 19th, 2006, 08:40 AM | #27 | |
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As a note, I randomly picked 6.5 mm......I have no idea what realistic measurements are.....this is just theoretical. Peace! |
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July 19th, 2006, 11:17 AM | #28 | |
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If you see an actual difference in your XLH1 FB setting each time you reattach a lens that has already been FB set, let us know. Best, Christopher |
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July 19th, 2006, 09:36 PM | #29 |
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Well there are several reasons to backfocus video lenes. For one thing remember your COC charts for film. larger circles for larger film formats. Also take into account that when light hits a frame of film it penetrates all the way to the back of the film.causing a chemical reaction. light must hit the front of a pixel for the image to be in focus> film thickness is massive compared to the surface of a pixel. video mounts are made of soft medals that actually expand and contract with temp changes. We will backfocus HD cams several times a day if the temps change. Film cameras do have shims placed behind the mount to correct for manufacturing tolerances being off. PL mounts are often reset or changed out as they wear on film cameras.
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July 20th, 2006, 01:41 AM | #30 |
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Adding to what craig said, not only do the temperature changes externally come into play but internally as well, I'm pretty sure there aren't too many film cameras with internal fans to regulate the temperature, this is common in the video counterparts.
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