FreeLists / opendtv / [opendtv] Re: Red camera lenses

["Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>]

Mark Schubin wrote:

>> Is color filtering on an individual pixel basis, the last
>> option you describe, what is used by digital still cameras?
>
> Yes.
>
>> I believe it is, and would seem to be the most compatible
>> way to make use of 35mm/APS lenses for video.
>
> From a fixed-focal-length image-quality standpoint, perhaps,
> but that's a tiny fraction of what a video lens must do. It
> needs to maintain focus, for example, over its entire zoom
> range (which, today, even in smallish lenses, tends to be
> around 20:1 and can go as high as 101:1 before the use of
> built-in extenders).

Thanks for all the informative responses, Mark.

So from all of this, I gather that if you have to accommodate the prism
or rotating wheel arrangements of the 2/3", 1/2", and 1/3" cameras, you
pay a penalty because you increase the image distance. An increased
image distance means you need a deeper camera and a longer focal length
camera lens, and a longer lens means a bigger aperture for a given
f-stop. So, as you say, a big lens.

Big lens, but small sensor area. Which means the big lens has to be very
good. Seems like the worst of both worlds, except that at least the good
lens measurements only need apply to a small image size, at the center
of what would normally be a large image area. So that works to the lens'
advantage.

By going to individual pixel color filters in the sensor, you may be
able to keep the same lens size or go to a smaller and shorter lens, all
else equal, use a bigger sensor area, allowing the glass to be of lower
quality, and the camera might even become smaller if the image distance
is reduced. You'd have to do the numbers to see exactly what the size
tradeoffs would be.

The zoom focus issue is actually an interesting one. I remember years
ago, on Modern Photography, that I think it was Herbert Keppler
discussed this. Earlier zoom lenses for 35mm cameras, say back in the
1970s, were more expensive. They tended to have fixed maximum aperture
over their zoom range, and the focus did not change with zoom setting.
But as zooms for SLRs became popular in those years, lens manufacturers
had to find ways to make them cheaper and lighter. So now you get the
variable max aperture over the zoom range, and the focus variation. But
of course, for 35mm movie cameras, you still want the better old-style
zooms.

Very interesting bunch of tradeoffs.

Bert
 
 
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