On Tue, 13 Feb 2001 07:48:44 -0600, "Richard Smedley" wrote:

>Yeah, it works the same way for telescopes. If you have a f4.5 Newtonian,
>then if you go from a 6" mirror to an 8" mirror, and maintain the focal
>length, you increase you light-gathering power by a factor of 1.8. This, of
>course, neglects the fact that you lose some because of a larger diagonal,
>etc. (I'm also not mentioning that maintaining an f4.5 on an 8" mirror is
>many factors more difficult than on a 6" mirror!)
>
>Sooo, why isn't anyone making add-on lenses whose sole purpose is to
>increase the light-gathering power for better low-light performance? I
>don't know anything about lenses (other than grinding my own 8" mirror years
>ago) so maybe it's not technically possible to make such a lens. It does
>seem theoretically feasible to me.
>
>Also, when discussing the low-light capability of any camcorder, it seems
>that all everyone talks about is the size and type of CCD, rather than the
>obvious other factor -- how about the lens?
>
>By the way, I'm not looking for any real answer here. Just discussing this
>issue in general.

Musing back...;-)
Most camcorders have lenses about the same "speed", which
are also at or near their cost/benefit point. To increase
speed much on most camcorder lenses would require noticeably
more expensive lenses (or lenses noticeably lower in imaging
quality). To add on an optical device that would effectively
increase lens speed would be impossible (the relative
aperture remains the same) - but you can maybe increase
lens speed slightly by adding a close-up lens of the right
power to a lens with enough excess focus range to still
be able to focus infinity-subjects with it attached. I
suspect the speed increase would not be enough to bother
with. (BTW, I have done this. With some close-up lenses
used for macro work, some zooms still allow infinity-focus
at the wide end [but I find this more useful for doing
"macro-focus-to-infinity" continuous shots...]). BTW,
people often assume that larger-front lenses pass
more light; this is not necessarily true - and enlarging
the lens front with a larger-fronted add-on does not
improve the lens' speed...