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hd lenses on single chip cameras


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#1 Keith Mottram

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Posted 02 April 2007 - 03:29 PM

when using a hd lens such as a digizoom on a digital camera like a red, will the t stop change?
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#2 Jonathan Bowerbank

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Posted 02 April 2007 - 03:43 PM

when using a hd lens such as a digizoom on a digital camera like a red, will the t stop change?


I'm not understanding why this question is being posed. Do you mean an HD lens as opposed to a 35mm lens being used on the Red?

I don't know for sure about that, there are a lot of factors to throw in. But a (potentially) good thing about the Red is that you won't need a Pro35 adaptor, so you're not worrying about having too much light loss.

If you're thinking of comparing HD lenses to SD lenses, then yes. HD lenses are generally more pristine and sharp than SD's, allowing in more light. I saw an example of the XDCAM HD being used, shot with an SD lens it looked horribly soft compared to the pristine Fujinon HD lens the rep was using for the rest of what he shot.
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#3 Max Jacoby

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Posted 02 April 2007 - 04:38 PM

Lenses for 3 chip cameras do not focus the different colors at the same plane so you cannot use them as such on 1 chip cameras (and film).

As far as I know there are adaptors, but I am pretty sure that you lose a certain amount of light for the very simple reason that these lenses are designed to cover a 2/3 inch surface and on bigger 1 chip cameras they have to cover a bigger surface. A related example would be the Cooke 18-100mm zoom that you can transform into a 9.5-53mm Super 16mm lens and in which case the speed increases from T3 to T1.6, which is nearly 2 stops.
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#4 Brian Drysdale

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Posted 02 April 2007 - 05:05 PM

There are two adapters currently* available that allow you to use a 2/3 video lens - one for 16mm and the other for Super 35. With the former, I'd imagine you'll lose some light because you're going through some extra glass. The RED would have to be windowed to allow you to use it, however, this wouldn't be an issue issue with the SI 2k on which you can use 16mm lenses.

With the Super 35 version the 2 stops figure sounds like the right ball park. It matches up with the figure for 16mm lenses modified to be used on 35mm.


http://www.abakus-sc..._Converters.htm


*RED are bringing one out, but I don't know if Abakus are making it for them.
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#5 Keith Mottram

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Posted 02 April 2007 - 06:25 PM

To clarify, if you were to use a red camera with a b4 mount (which is listed as an option) and a digizoom which is I believe T1.9 at fully open would you achieve the same T stop or would that T stop change due to the fact that it is mounted on a single rather than 2/3 chip? For example if an HD lens opens to T1.9 on a 2/3 chip this aprox T4 on 35mm, if the same lens is on a single chip is T1.9 still T1.9 or would the T stop be different? I am primarily thinking of depth of field rather than the amount of light needed to achieve the T stop. Further more would there be any optical advantages/ disadvantages in using digiprimes/zooms as oposed to 35mm lenses on a camera such as a red?

Edited by Keith Mottram, 02 April 2007 - 06:27 PM.

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#6 Max Jacoby

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Posted 02 April 2007 - 06:49 PM

For example if an HD lens opens to T1.9 on a 2/3 chip this aprox T4 on 35mm, if the same lens is on a single chip is T1.9 still T1.9 or would the T stop be different?

In this case T1.9 would be T4.

As a real life example of how this works, Arri have an 18-100mm Cooke Zoom adapted to their 765 via a relay tube and the lens is recalibrated to a 34-210mm with a stop of T6.3.

I don't think there would be any optical advantages in using DigiPrimes on a 1 chip camera, as the existing 35mm primes are specifically designed for this and not used via an adaptor. Also compared to their 2/3" equivalents 35mm primes have longer focal lengths for the same field-of-view. The longer the focal length the easier it is to reduce distortion during the design so 35mm primes will look better than the much shorter DigiPrimes.
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#7 Brian Drysdale

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Posted 03 April 2007 - 04:26 AM

I can't see any advantage sales wise in RED having their B4 adapter option covering the full 35mm area. The larger market demand would be to be able to use 2/3" HD lenses for documentaries plus TV dramas. With all the full 35mm DOF marketing, it's easy to forget that windowing is a feature on the RED, so you can use the 2/3" lenses as normal.

The main advantage of the 2/3" to 35mm single sensor/film adapter would be in using those large zoom range HD video lenses used in sports coverage.
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#8 Keith Mottram

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Posted 03 April 2007 - 04:28 AM

thanks everyone for filling in my knowledge gaps...
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#9 Eden Lagaly-Faynot

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Posted 03 April 2007 - 06:23 AM

Lenses for 3 chip cameras do not focus the different colors at the same plane so you cannot use them as such on 1 chip cameras (and film).


Hello Max,

The light coming out a lens is split by a prism into the 3 primary Red Green Blue right? Since the prism is located into the body of the camera, I can't get why B4 mounted lenses wouldn't focus colors on the same plane?
Maybe I miss something?

Thanks,
Eden.
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#10 Brian Drysdale

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Posted 03 April 2007 - 08:44 AM

Hello Max,

The light coming out a lens is split by a prism into the 3 primary Red Green Blue right? Since the prism is located into the body of the camera, I can't get why B4 mounted lenses wouldn't focus colors on the same plane?
Maybe I miss something?

Thanks,
Eden.


Historically, when video cameras had tubes, they agreed to save money on lenses by not fully correcting for chromatic aberration. So, instead of putting the tubes the same distance (as with a corrected lens), they put the tubes at different focal distances to match each colour. This got carried over when CCD's replaced tubes in video cameras, so each CCD is at a slightly different focal distance.

Of course, you could adjust the tube's focal distance to match the lens, which you can't do with prism mounted CCDs. So the lenses now have to be made to a higher standard than the old tube video lenses to focus each colour on it's fixed CCD.
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#11 Eden Lagaly-Faynot

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Posted 04 April 2007 - 01:22 PM

Thanks Brian for the historical explanation!
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