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Collimating TV lens for Bolexes...


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#1 Sir Alvin Ekarma

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Posted 16 May 2006 - 05:22 PM

I just want to double check: if you get a c-mount TV lens, it needs to be recollimated if you want to use it with a film camera i.e. Bolex, right?
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#2 Charles MacDonald

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Posted 16 May 2006 - 08:03 PM

I just want to double check: if you get a c-mount TV lens, it needs to be recollimated if you want to use it with a film camera i.e. Bolex, right?

IN THEORY, It shoulld work Ok an almost any c-mount EXCEPT Bolex, BUT it is real easy to adjust the backfocus on a TV camera so The lens May Not be set up just right.

Two other posible problems.

1) I have at least one TV lens that will not clear the shutter in my Filmo. TV cameras just had a sensor in many cases - Often a 1 Inch Vidicon, and so the lens could get away with almost touching the sensor.

2) the BOLEX has that Prisim/beamsplier gismo, a normal everyday lens will need to be checked out and posibly adjusted to ensure that the focus in the finder is right.

ALSO

I have seen a lot of TV lenses with out diapharms, and I am sure that many more were just loosly calibrated. A vidicon can have its sensitivity controled by playing with the target voltage. So You may want to have that checked also.
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#3 Sir Alvin Ekarma

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Posted 16 May 2006 - 08:51 PM

Thanks for the info. I was buying a lens from a fella on Ebay and he was the first person I've communicated to say that TV lenses didn't need to be adjusted. (I guess he's half right if you don't count a bolex). Anyway, I got a computar lens for cheep and I'll probably have JK camera adjust it sometime.
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#4 Clive Tobin

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Posted 16 May 2006 - 09:41 PM

I just want to double check: if you get a c-mount TV lens, it needs to be recollimated if you want to use it with a film camera i.e. Bolex, right?


This has been asked many times!

The prism in the Bolex Rex cameras causes dispersion errors in an ordinary lens. This means that the refractive index of the prism is not uniform for all colors of light. So with an ordinary lens, if the green light is in focus the red and blue are not.

The Bolex RX lenses are designed to offset this dispersion error by introducing an equal and opposite error to ensure a sharp image.

Dispersion error cannot be corrected by collimating a lens. It requires a different lens formula.

Collimating a TV lens might help a little if it is not collimated perfectly in the first place. Some lenses seem to manage okay with the Bolex prism if stopped down a bit, others are terrible at almost all settings. You need to try it out with film tests to see.

Some TV lenses are not very good to begin with since TV is not as sharp as film, so the lenses are designed to looser quality standards.
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#5 Sir Alvin Ekarma

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Posted 18 May 2006 - 11:21 AM

I dropped a line to Chambless and they said TV lenses didn't need to be adjusted if used with an EBM. And if anybody should know, I guess it would be them...
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