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Old April 29th, 2008, 05:32 PM   #16
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Sorry to further this tangent, but for the sake of other readers, I think its important to get to the bottom of this. That way, there isn't another thread on the internet with incorrect figures.

I think you may be mixing up some information, F-stops don't accurately measure light transmission, so I don't see why they would be used by a manufacturer to identify light loss from a prism system.And just to be precise, the Digiprimes maximum T-stop vary from T1.6 to T1.9, there inst a T1.4, and if it were possible to effectively make a T1.0 lens for a 3-chip HD camera system, I can guarantee it would have already been done by Zeiss, Canon or Fujinon (and there would be people willing to pay $20,000 more for it). The purpose of having such a fast stop on a 2/3" camera would be for achieving a Depth of Focus similar to s35mm, it wouldn't necessarily be for "low-light" applications, as you would be silly to have the budget to use digital cinema equipment, but not have the budget for a proper lighting equipment. Also, The lenses you listed with an aperture with greater than f1.4 are for machine vision and security applications, most (if not all) design for single ccd/cmos cameras, just because a website that sells security lenses says that a lens with a maximum aperture of f1.2 is "3-CCD compatible " does not mean your going to get a usable image at an f-stop greater than f1.4 on a 3-ccd camera.

Forgive me if I am incorrect, but if your certain about your information regarding the proper use of Lenses with a maximum aperture greater than F1.4 of 3-CCD prism professional camera systems please provide some cited material explaining your stance. Sorry if I sound like a jerk, I just want make sure there is accurate information being provided, and if I am incorrect, I want to make sure I don't spread incorrect specifications.
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Old April 29th, 2008, 06:13 PM   #17
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I hope this isn't adding fuel to fire, but as a LEX/HD100 owner, I have searched high and low for options being discussed on this thread. I threw out security lenses lens early on because all these wide aperature,3-ccd lenses are primarily C-mount lenses which have somewhere around a 17mm flange focal distance. The 1/3" bayonet mount on the JVC's is around 31mm. This means you would somehow have to get that C-mount lens closer to the CCD than the actual lens mount which would mean dismantling and doing some camera surgery that is just too risky to even bother with.
The reason the DIY relay was somewhat effective with the 24mm SLR lens was (and someone can correct me if I am wrong) the 46.5mm flange distance for Nikon-mount lenses is well in front of the 31mm flange of the 1/3" bayonet of the JVC so you simply needed a mount adapter or mount/extension tube to bring that 24mm out a few more millimeters in order for focusing to occur.

In short, I think it's safe to say C-mount lenses are out.

Now if someone is willing to get the proper measurements, do the correct math, and gather up some R&D money, you might be able source and build a relay lens yourself. I started doing this myself with edmundoptics.com but backed out as costs kept increasing just for research. Prototypes are not cheap.

Remember when we all loved our JVCs for that fully manual stock lens and that was enough?
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Old April 29th, 2008, 06:13 PM   #18
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I think quite the opposite - how can lens's iris possibly affect limitations on how wide you can go with the iris in regards to the CCD block ? closing down too far you get pinhole effect, but thats still more of a lens issue vs sensor size, not a CCD block issue.

regardless of T vs f stop in rating light loss, its a number people can relate to in regards to light loss. All I see a prism rated at F1.4 is saying whats hitting the chips vs whats coming in. nothing more. it does not in any way indicate what sort of lens is suitable for use with that block, and I'd really ask for some white papers indicating this and why.

here is some basic info on the prisms


a techincal paper on 4CCD blocks without any mention of lens choice but a lot on CA, noise, resolution. not one mention of CCD block design limiting lens selection


as for the small lenses I did find, the point wasn't that they don't exist, its that they do. I'd love to try putting one onto the front of my camera but I think the problem with C mount glass is that they don't have a deep enough backfocus for at least my HD100 to get infinity focus. maybe they aren't the sharpest, but thats not the goal, light transmission and size are, along with price.

I still say, a T1 lens is just too much of a problem to build. in the movie world were money is far less an object then in video, there should be plenty of these lenses but there aren't, and comes down to size and wieght more then anything else, then price. if panavision could make'm, they would, but they don't. thats not so say there aren't some, kubrick used them in barry lynden, but I'm sure they were a beast to work with and they where custom built.

other reasons may come down to controlling CA becomes much harder that wide open, overall lens flare, and again it becomes too expensive to do. every market has a price point, even in hollywood.
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