Re: [APML] Dynamic Range of CCD

[Matt BenDaniel <matt@starmatt.com>]

Loke,

I agree with everything you are saying. CCD's do have wider dynamic range. It is NOT just bit depth.

With NABG cameras, dynamic range is very important, especially for shorter telescopes. Peak signals will be from the bright stars, which you do not want to bloom. CCD noise is well below the noise of film (its grain). For example, I don't think anyone will ever record the depth of Tony's M51 on film.

But even under light polluted skies, it is primarily CCD's high dynamic range that makes good imaging possible. The linearity, lack of toe, and high QE all have advantages, but the biggest single factor is dynamic range.

Matt

At 01:48 PM 4/5/2002 -0800, lkt wrote:
>Gene,
>
>        Burning out film depends on the film <g>, and I am not talking about
>printing. So printing and scanning is a non-issue. As you know TP/D19
>can easily burn out but not so with color negatives. However, with color
>negatives, the apparent wide dynamic range is more like the logarithmic
>approach to the saturation point. I believe the information recorded in
>color emulsions to also be quite a bit lower in dynamic range than CCDs
>(ST10). The wide dynamic range and linearity in CCDs allows one to
>capture the brightest to faintest light levels with fidelity even though
>you cannot see it. For scientists, this is what matters most. For us
>pretty picture imagers, we can use dodging/burning in Photoshop or DDP
>to map the 12-13 bits of dynamic range to a visually perceivable image. 
>
>Loke
>
>
>Gene Horr wrote:
>> 
>> lkt wrote:
>> 
>> >         I think the wide dynamic range is quite important. There are many DSOs
>> > with very wide dynamic range, mostly galaxies with bright central cores
>> > and globular clusters. It is rare for an ST10 to burn out on any of the
>> > cores of such objects.
>> 
>> But in real world use what is the difference between the lowest level and
>> the highest level effectively recorded on one of these galaxies?  From
>> my personal experience in dealing with 20 minute to 1 hour exposures
>> it is rare to get a useful range beyond 1,000 ADU counts.
>> 
>> For that matter from film experience it is also rare to "burn out" the
>> film _when_making_prints_by_someone_who_knows_what_they_are_doing_.
>> >From what I have seen most affordable film scanners are not recording
>> all of the information that is in the film.
>> 
>> If you look around the comparisons are actually being made between a
>> particular CCD camera and a particular film scanner, not between
>> CCD & film.
>> 
>> As an aside - I shoot a heck of a lot more CCD images than I do film.
>> But the reason are more to do with laziness than because I find CCDs
>> inherently recording more information.
>> 
>> Gene Horr
>> genehorr@texas.net
>> 
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--
Matt BenDaniel
matt@starmatt.com
http://starmatt.com


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