On Wed, 19 Mar 2003 00:38:30 GMT, "ralford"
<ralford@bigfoot.com> wrote:
>From: "Neuman - Ruether"
<d_ruether@hotmail.com>
>> On Tue, 18 Mar 2003 16:13:59 GMT,
"ralford"
>> <ralford@bigfoot.com> wrote:
[...]
>> >And the intensity does indeed change for
different image areas as we all
>> >expect.
The fact that is varies as the square emphasizes the effect.
>> >
>> >I'm happy now :)
>> But, I'm not....;-)
>Damn, me neither. Looking at my little equations, I
think I just returned to
>the same point. i.e.
>
>since the total size of the two ccd's is proportional to
d^2,
>
> ( E1/ d1^2) / ( E2/d2^2 ) = 1 .... crap! back where I started.
>> It is all really much simpler than all of this,
>> really....;-) If you are comparing two CCDs for
>> relative sensitivity, based on size alone, the
>> whole lens issue is irrelevant (you could stop
>> right there...;-),
>agreed, however, we cannot ignore the amount of light
arriving at the ccd.
>There is no doubt that a larger CCD is more sensitive
since it has a larger
>area to integrate the light over.
Yes - but a simple specification that the
illumination of the same subject is the same, and
that the same f-stop is used on both lenses (which
properly cover their respective CCD sizes) cover
this...
>> since all relevant aspects
>> for the lenses used, if properly specified, are
>> the *same* for the two different CCD sizes, and
>> therefore the lenses can be dropped from the
>> comparison equation.
>This is were the problem comes from. Clearly the same lens cannot give the
>same result, since the length characteristic (wide,
normal, tele) depends
>upon the size of the element. Granted a smaller ccd can be put in place of
>the larger ccd, however, the characteristic, as used,
will change. And in
>fact, the smaller ccd would gather an appropriately
smaller amount of the
>light gathered by the large ccd.
The last is true, as I have tried to point out, but
the earlier part isn't. The FL, max aperture, lens
diameter, etc. are all irrelevant if the lenses
cover their respective CCD areas, and can be set to
the same aperture (easily satisfied conditions...).
>>It does not matter if the
>> lens for one is a tele, and the lens for the other
>> is a WA (assuming even illumination), nor if one
>> lens is bigger in diameter, or whatever. If the
>> lenses are correctly focused on the same (distant)
>> subject, with the same reflectivity and
illumination,
>> and both lenses are set at the same aperture (and
>> have the same efficiency), and both cover their
>> respective CCDs, and are used at the same relative
>> aperture, then their contribution is the same for
>> both CCDs - they both pass the same "unit
intensity"
>> of light to the CCDs, with the larger CCD obviously
>> receiving more "units".
>Sorry, I don't think all those conditions can hold at
the same time. The
>focal length must change to preserve the characteristic,
Not necessary at all...
>and the light
>intensity is a function of the focal legnth and the
aperature.
No it isn't - it is a function of relative aperture
and the light entering the lens (both conditions are
the same for both lenses...).
>I am willing
>to assume lossless lense for this discussion. To "cover their respective
>ccd" is the problem.
Not really, since nothing matters but the
easily-satisfied conditions of sufficient coverage
and the choice of the same f-stop... (hate to keep
repeating this, but this is true - and once seen,
the "solution" is easy...;-).
>>Better to simply remove
>> these confusing-but-equal-in-effect lenses, and see
>> the obvious directly: the two CCDs, under the same
>> even illumination, with the same type of
construction
>> (including sensor type and number, but not sensor
>> size, which would change proportionally with chip
>> size), will not be equally sensitive; the larger
>> will be more sensitive...
>> I'm not sure why this is so difficult...;-)
>Me neither :)
It is easier to understand that Vegas!
(not trying to start
>a NLE jihad, vegas-newbie ranting....)
No prollem...;-)
>Cheers,
>
>Richard