On Thu, 14 Dec 2000 12:52:28 GMT, "Alexander Ibrahim"
>"M.A. Smith"
>news:3A387B0E.69506B14@moving-memories.com...
>> Alexander Ibrahim wrote:
>> Snip
>> > I just intercut a little more than 4 hours of footage from these
>cameras. In
>> > that setup the XL-1 was nearly twice as far from the stage as the
>TRV900,
>> > and still the images from the TRV900 were not as bright.
>> Snip
>> I believe that the distance of the light source from the subject is the
>> important factor here, not the distance of the subject from the camera
>(unless
>> there is some atmospheric condition or the distance is vast). The exposure
>> should be the same whether you are 2, 20 , or 200 feet away.
>>
>> I am correct here, right??
Yes.
>No that is not true, emphatically so.
>
>Remember the lighting rule...The strength of light falls off with the
>inverse square of the distance. Now think of it this way...what you are
>weilding when go to a shoot is a light meter that happens to make a lot of
>simultaneous measurements and records them for your review. Another way of
>looking at it...you are using light reflected from the subject to light your
>imaging surface.
>
>Because of the strange nature of light, we get to disregard this to some
>extent, because of our zoom lenses. At wide angles light from a huge area is
>gathered and you see the intensity fall off. As you zoom, you still gather
>light from the same area, but you are changing the plane of focus so you get
>a different part of the light. This bending of light onto a small imaging
>area kind of acts like a magnifying glass when you are trying to kill ants.
>
>Of course your zoom lense also hurts you...your f-stop is likely to crawl up
>a full stop or more as you go from wide to tight. I would have killed to get
>20 feet closer, I could have dropped my f-stop to 1.6 instead of 2.0. Of
>course if I could get them to raise the lighting ...
>
>However when you are far away a lot less of those photons will get to your
>imaging plane through your optics. Remember the photons you are trying to
>corral are spreading to a relatively huge surface area. Even with a fairly
>large 72mm lens to gather the light you only have about 4071mm^2 of photons
>to look at. 20 feet is very different from 40 feet. 80 feet is worse..and so
>on.
>
>If the subject is properly lit for video it almost won't matter. Now a bad
>lighting situation, like I had, will exacerbate the limitations of your
>optics and imager. I was shooting a dance troupe, in a large auditorium with
>lights so low, I could barely see with my eyes...you know for dramatic
>effect. {sic.}
>
>Also since my light is reflected, from the subject only the light incident
>on the subject gets put into the lighting equation. If I really wanted to
>calculate from the light setup I'd have to add the distance from the light
>to the subject and the distance from the subject to the camera. How do I
>calculate this mathematical wonder ? Starting at about 20 feet from the
>subject, for every ten feet I move away the lighting people should pretend
>their lights are 1 foot farther away. At 50 yards they should light like
>their lights are 12 feet further from the subject than they are.
Nice try, but, assuming no loss due to the intervening
medium (here, air...), there is no loss in light level
due to the distance of the observer (otherwise, the sun
and moon would be MIGHTY dim...! ;-).
>There is a small adjustment to be made since my glass has four times the
>area of the TRV900's, but it is really negligible.
If the f-stop is the same, and the designs equally
roll off edge illumination, there is no difference
in light transmission due to front-element diameter
of a lens. A tiny 20mm f2 lens makes as bright an
image as a big 200mm f2; a smallish-front 20mm f2
(all else being equal) passes as much light as a
largish-front 20mm f2...) If the area of the diaphragm
of one lens is four times that of the other at the same
focal-length, it passes two stops more light, hardly
a negligible amount of difference...;-)
BTW, in my reviews, at: www.David-Ruether-Photography.com/camcorder-comparison.htm ,
I based my conclusions on overall performance, though
in specific light levels, the conclusions could very
well be different. I liked the picture quality of
neither Canon reviewed, though in a specific room
interior light-level, both performed at their best
(and better than some others - but it is reasonable
to assume that not everything will be shot at this one
light level, and in most other situations I preferred
the picture quality of other camcorders...;-).