Digital vs. Film in Astrophotography

Chris,

You have it backwards. Because film is nonlinear, it has a greater dynamic
range than a CCD. Don't confuse range with sensitivity. CCDs are more
prone to oversatuation than film. For example, a single unprocessed
exposure of the Orion Nebula will turn out better on film that on a CCD with
regard to dynamic range.

Also, the original poster meant to say that film has more definition rather
than more resolution. Definition is the pixel count (like HDTV); resolution
is the pixel size coupled with optical performance.

Del Johnson



"Chris L Peterson" wrote in message
...
On Sun, 28 Dec 2003 21:11:27 -0800, "Jason Donahue"
wrote:

OK, so that's the basic argument as to the superiority of digital over
film
in astrophotography, and it makes sense. However, is CCD imaging really
that much better? For example, the CCD has to be cooled to cut down on
noise, an issue you don't see with film.

Does that matter? A digital camera designed for long exposures _is_
cooled, so
it is that cooled camera you are comparing to film.


Also, the majority of CCDs in use
are smaller than 35mm film format - wouldn't that generally mean poorer
maximum resolution?

It depends on your ability to match your optics to your imager/film. CCDs
(with
pixels in the 5-10um range) are higher resolution than most films at the
focal
plane.


I mean, some of the better 35mm films give incredible
resolutions, and, combined with 40 megapixel film scanners, you get
better
resolution than digital.

There are very few films that (in 35mm format) deliver anything close to
40
megapixels. At best, typical color films used by most astrophotographers
can
yield spatial data at around 5-10 megapixels, and that varies with
contrast. The
MTF for a digital sensor is flat, so you get uniform response regardless
of
contrast. Since film is non-linear and doesn't have much dynamic range,
you have
to deal with much lower intensity resolution.

Not really. Many color films work just fine uncooled and unhypered. It is
mostly the Tech Pan B&W film that needs the boost.

Del Johnson


"Roger Hamlett" wrote in message
...
For the highest sensitivity, film needs to be cooled, and hypered. The
difference here is unimportant, since an astronomical CCD, will have the
cooling built in.

On Mon, 29 Dec 2003 11:22:01 -0800, "Del Johnson" delastro@{right star in
Orion's belt}.sdsu.edu wrote:

Chris,

You have it backwards. Because film is nonlinear, it has a greater dynamic
range than a CCD. Don't confuse range with sensitivity. CCDs are more
prone to oversatuation than film. For example, a single unprocessed
exposure of the Orion Nebula will turn out better on film that on a CCD with
regard to dynamic range.

I don't have it backwards at all. At the ends of the "S" curve you get with film
the range is compressed down to the noise level. A decent CCD detector will have
between 10 and 50 times the dynamic range of a good film.

Yes, a single exposure on the film may turn out "better" because the film is
compressing the range- that is, you are losing information at the top and
bottom. IMO that is not an advantage; I see how some might see it that way,
though.


Also, the original poster meant to say that film has more definition rather
than more resolution. Definition is the pixel count (like HDTV); resolution
is the pixel size coupled with optical performance.

Yes, the terminology is a problem here. Different disciplines use the same words
in quite different ways. In terms of pixel count, I'd say that a typical 35mm
color film is somewhere between 2 MP and 10 MP, depending heavily on the
characteristics of the image. A typical CCD these days is between 1 MP and 4 MP,
but without the dependence on the image. So the spatial information content
isn't all that different between the two, and CCDs are rapidly becoming higher
density devices.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

For the highest sensitivity, film needs to be cooled, and hypered. The
difference here is unimportant, since an astronomical CCD, will have the
cooling built in.


An engineer I knew who was into astrophotography used to cool his B&W
film and then in the 30 minutes before loading it into the camera would
HEAT it to about 45C...he built a very small regulated oven for the
purpose. If I remember correctly, he claimed this made the film more
sensitive (I would expect noisier as well).

Comments?

Alan

"Davoud" wrote in message
...
Michael A. Covington:
...A good 6-megapixel cooled CCD camera should outperform 35-mm film for
astrophotography. (Bear in mind that for smoothness, you often have to
"bin" the pixels 2x2, which reduces the number of megapixels to a
quarter of
what it was; 1.5 in this case.) SBIG has a camera in this range, priced
at
$15,000 to $45,000 depending on the grade of CCD. Big observatories
have
even bigger ones, up into the 100 megapixel range, but they cost a
fortune.

"A fortune" is quite relative. I'm trying to imagine myself telling my
wife -- aka "the breadwinner" -- that I want to spend $15-$45k on a CCD
camera. "You've been raving about the F3 that you bought on Ebay. All
of a sudden it's no good and you want to spend a fortune on a CCD
camera?"

I should add that contrary to what people often think, as a book author I am
not rich. I too consider a Nikon F3 to be a luxurious camera. And I use
one. For me, $15k is too much to pay for a car, much less a camera.


--
Clear skies,

Michael Covington -- www.covingtoninnovations.com
Author, Astrophotography for the Amateur
and (new) How to Use a Computerized Telescope

"Chris L Peterson" wrote in message
...

You have it backwards. Because film is nonlinear, it has a greater
dynamic
range than a CCD. Don't confuse range with sensitivity. CCDs are more
prone to oversatuation than film. For example, a single unprocessed
exposure of the Orion Nebula will turn out better on film that on a CCD
with
regard to dynamic range.

I don't have it backwards at all. At the ends of the "S" curve you get
with film
the range is compressed down to the noise level. A decent CCD detector
will have
between 10 and 50 times the dynamic range of a good film.

The real problem, as you point out, is that with film, the toe is
compressed. We would rather have the toe be perfectly linear and do our
compression, if any, at the shoulder, because the faintest objects in the
picture are usually the most important. Also, the compressed toe works
against you if you want to stack images or subtract out the sky background.

I seem to recall that CCDs typically have a 12- to 16-bit dynamic range. 12
bits is 12 stops, photographically speaking; film is 9 or 10 stops maximum
when developed normally, much less when processed for high contrast in
astronomy.

Michael A. Covington wrote:

I should add that contrary to what people often think, as a book author I am
not rich. I too consider a Nikon F3 to be a luxurious camera. And I use
one. For me, $15k is too much to pay for a car, much less a camera.



That's a shame. It's a good book and you deserve to be rich. macnmotion

On Mon, 29 Dec 2003 17:19:40 -0500, "Michael A. Covington"
wrote:

I seem to recall that CCDs typically have a 12- to 16-bit dynamic range. 12
bits is 12 stops, photographically speaking; film is 9 or 10 stops maximum
when developed normally, much less when processed for high contrast in
astronomy.

The sensors in most commonly used cameras have dynamic ranges of 76-78dB, or
about 13 bits. A couple of cameras are as high as 85dB (14 bits); that's as high
as any sensors I'm aware of amateurs using. There are some tradeoffs. If you
really want a lot of pixels (11M) for not too much money, you could go with the
SBIG STL-11000M, but then you get a sensor with rather poor performance: only 11
bits of dynamic range, shallow pixels, poor linearity, and microlenses. Of
course, with a linear detector, you can just take more pictures- every time you
double the number it is like you added another 6dB, or one stop. This kind of
stacking is very imperfect when applied to film, because you've already lost the
information down at the low intensity end of the range, and because adding
non-linear frames just makes things less linear.

It is important to remember that lots of pixels (or the film equivalent) is
really only important for wide field imaging. For the vast majority of DSOs, one
or two million pixels is more than enough to reach the point where the seeing
and optics are the limiting factor, not the sensor pixel count.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

"macnmotion" wrote in message
...
Michael A. Covington wrote:

I should add that contrary to what people often think, as a book author I
am
not rich. I too consider a Nikon F3 to be a luxurious camera. And I use
one. For me, $15k is too much to pay for a car, much less a camera.

That's a shame. It's a good book and you deserve to be rich. macnmotion

Persuade a million of your friends to buy my books and I will be

Actually I should be careful about saying "I'm not rich" because I've
recently come across people who really look down on me for not being rich.
This is a value system that I don't understand. But right now, with
daughters in and approaching college, I'm not going for high-budget
equipment.

Anyhow, the audience for my books is primarily people with common equipment,
so if I bought really high-end gear, I'd actually become less qualified for
the writing that I do. My main endproduct is not astrophotos -- it's
knowledge of how to make astrophotos.

Thank you for your support!

Michael

Don Stauffer

Ah, but serious astrophotographers DO cool film in film cameras, and do
such fancy things as presensitizing film with various gases and
chemicals.....

Hypersensitizing yes but I think you will have to dig very deep to
find anyone cooling film cameras these days.

In the days before TechPan, cooled cameras were a must but I think
everyone getting into astrophotography since than is mighty glad they
don't have to deal with cooling.

I would be interested in knowing who, if anyone, has any info on
cooling TechPan and if it helps much.

One more point while I am at it, browsing this thread I have not seen
any mention of film grain size.. just a lot of converted electonic
jargon. If anyone has ever looked at a piece of film under a
microscope and then looked at a CCD chip, the argument about
resolution would be pretty moot.

Authors in older books make all sorts of strange claims for the grain
size in film but if you look at the grain under a microscope, you will
realize how shaky these statements are. The pixel is a well defined
rectangle while the film grain looks like a blob of jellow running
down a wall and is sigficantly larger to boot.

Take a half inch square of a film photo and fill you monitor with it
and you will get the idea. CCD resolution is vastly better.

Keep an eye on my web site and see how the old film phots get replaced
by CCD images as time goes by.

js

PHOTO OF THE WEEK... http://schmidling.netfirms.com/weekly.htm