Digital vs. Film in Astrophotography

"Jack Schmidling" wrote in message
m...
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.

I researched this a few years ago... It has been shown that most cooled
cameras were too cold. Cooling the film too much reduces the speed.

Cooling hypered Tech Pan should not help, for the simple reason that once
the reciprocity failure is near zero, there's not much possibility of
lowering it any further. At some point you get very close to zero
reciprocity failure, and there you stay.

Ditto for new-technology color films that already have little reciprocity
failure.

Cooling worked miracles with one generation of color films, back in the
1970s. Films have changed.

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.

What I think you're getting at is that the film grain is *irregular* -- you
will see granularity in a film image even when you're not near the
resolution limit, because of random large-scale variations. In a digital
image, you do not see granularity until you approach the actual resolution
limit.

Keep up the good work!


--
Clear skies,

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

I have sort of a different view of this issue. I own a professional
photo studio and lab (film based) and am also an avid
astrophotographer. I use both film and CCD and find that each has its
own strong points. While I don't do commercial CCD photo work in my
business (mostly all medium and large format film work)...it is very
obvious that film will soon be a very limited market. The convenience
of digital for Joe average is an easy sell for the convenience,
cross-platform ability (can be printed on home color printers, saved
on computer storage media, etc.) You can also email pics to your
friends. That being said...film for THAT purpose still has the edge in
quality, etc. but only when processed by good labs and knowledgeable
technicians. The average suff you get from the one hour labs is pretty
poor quality and the average digital photo printed out on your $200
color printer at home will likely be better! But film is quickly
dissappearing as CCD is leapfroging with the latest innovations. Even
the traditional film areas like large format photography are changing
over to digital. Of course this isn't cheap...it isn't unusual for a
CCD back for a large format camera ALONE to run over $35,000. This
doesn't include the huge overhead in very high end computers and
computer storage...and large format computer color printers.

The bottom line is that as film becomes more and more of a dead end
media for the masses...you can count on good films suitable for
astrophotography to also go away.

The other differences are that in film there is about a 5% efficiency
ratio...5% of the photons hitting the film are saved. In CCD there is
about a 95% efficiency ratio. This accounts for the greater
sensitivity of a CCD. In addition the response on CCD is lineal or
nearly flat in response. On film even the best ones still have
reciprocity failure...doubling the exposure won't give twice the
photons....you need a longer exposure. This last is probably the main
reason scientists prefer CCD....CCD is lineal...twice the exposure
time doubles the photons captured. From a science standpoint that is a
huge advantage.

And yes...I prefer CCD for astronomy....although I still use film for
wide field imaging. Big chip cameras suitable for covering a wide FOV
and maintaining a favorable sampling ratio are still too
expensive...but they are getting cheaper. However I see the consumer
type big chip digital cameras like the Canons replacing the dedicated
CCD astronomy specific cameras for the average person in a short time.
However, the better IR and blue response and lower noise of a CCD
camera designed for astronomy will still be the instrument of choice
for serious scientists and advanced amateurs for a long time.

Bob Berta

In article , Robert
Berta writes

The other differences are that in film there is about a 5% efficiency
ratio...5% of the photons hitting the film are saved. In CCD there is
about a 95% efficiency ratio. This accounts for the greater
sensitivity of a CCD. In addition the response on CCD is lineal or
nearly flat in response. On film even the best ones still have
reciprocity failure...doubling the exposure won't give twice the
photons....you need a longer exposure.

Film reciprocity failure does not quite work the way you suggest. It's
not that "twice the exposure doesn't mean twice the photons": it's more
a case of "half the rate of photons per second gives less than half the
nucleus sites". This is because (simplifying a complex situation
somewhat) a stable nucleus site requires several Ag atoms, which in turn
requires several (typically 3) photons to create. If a single Ag atom is
left alone for too long before being joined by others it will be lost
and no "exposure" is registered. At "normal" light levels this is
unlikely to happen, but as the level reduces it becomes more probable.

Twice the exposure always (even in the region of severe reciprocity
failure) results in twice the recorded density, as long as you are in
the linear area of the film's characteristics; it just may not be as
much density (for either length of time) as you expected.
--
David Littlewood

It is this "compression" that gives film greater range. The CCD may
distinguish more levels of brightness, and is certainly more sensitive, but
film prevails when there is a large difference between bright and dark
objects in the same image.

Why would this not be an advantage? The alternative is a complete loss of
detail in the oversaturated areas.

Del Johnson



"Chris L Peterson" wrote in message
...

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.

On Tue, 30 Dec 2003 15:21:14 -0800, "Del Johnson" delastro@{right star in
Orion's belt}.sdsu.edu wrote:

It is this "compression" that gives film greater range. The CCD may
distinguish more levels of brightness, and is certainly more sensitive, but
film prevails when there is a large difference between bright and dark
objects in the same image.

Why would this not be an advantage? The alternative is a complete loss of
detail in the oversaturated areas.

It's not an advantage because you pay for your lack of saturation at the bright
end with a huge loss of detail at the dim end (everything is compressed into a
very narrow brightness range). It is precisely in the ability to show detail at
the dim, low contrast end of things where CCDs shine, and that is the region
that is usually of the most interest (to me, anyway) when examining astronomical
objects.

_________________________________________________

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

Sounds like you are still confusing range with sensitivity. It is a given
that a CCD will pick up fainter objects for the same integration. If one
adjusts the integration time so that the faint range is about the same
between film and CCD, one will find that film will be less likely to
overexpose the brighter portions of the image.

Any single unprocessed CCD of the Orion Nebula that shows the fainter wisps
will completely burn out the bright core, whereas a film image will do a
better job of capturing the entire dynamics of this object (albeit with a
longer exposure). The only good images of the Orion Nebula with a CCD are
a result of multiple stacked images or mosaics that have been pumped up with
paint software.

Del Johnson


"Chris L Peterson" wrote in message
...

It's not an advantage because you pay for your lack of saturation at the
bright
end with a huge loss of detail at the dim end (everything is compressed
into a
very narrow brightness range). It is precisely in the ability to show
detail at
the dim, low contrast end of things where CCDs shine, and that is the
region
that is usually of the most interest (to me, anyway) when examining
astronomical
objects.

_________________________________________________

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

On Wed, 31 Dec 2003 10:08:49 -0800, "Del Johnson" delastro@{right star in
Orion's belt}.sdsu.edu wrote:

Sounds like you are still confusing range with sensitivity.

Not at all. Sensitivity is a whole separate issue, and I'm not discussing it at
all.


Any single unprocessed CCD of the Orion Nebula that shows the fainter wisps
will completely burn out the bright core, whereas a film image will do a
better job of capturing the entire dynamics of this object (albeit with a
longer exposure).

You are fooling yourself here. Most film has an overall dynamic range of about
3A, or maybe 3.5A if you really push out into the extremely non-linear portion
of the response curve (that is, where a factor of 10 difference in source
intensity produces essentially the same density on the film). Most CCDs have an
overall dynamic range of about 78dB, or 3.9A, and that is nearly linear end to
end. The simple fact is that if you make a single CCD exposure of the Orion
nebula adjusted just to the point where the core is about to saturate, you will
have captured more detail at the wispy edges than the film image will give you
assuming that you expose it long enough to compensate for the difference in
sensitivity.

The trick with film is that you can expose it even longer than that in order to
bring some of the wispy detail up on the image, and still have a reasonable
looking core. But even so, that core has been pushed up onto the flat part of
the response curve, which means that much of the structural detail has been
obliterated, even if it doesn't have the characteristic blown-out appearance of
a saturated CCD image.


The only good images of the Orion Nebula with a CCD are
a result of multiple stacked images or mosaics that have been pumped up with
paint software.

I think this is a bit of an exaggeration, but if not, so what? In what way is
taking multiple CCD images a problem? There is virtually no difference in effort
between taking one CCD image or taking several, and the overall exposure time is
still shorter with the CCD. So if the normal CCD technique involves collecting
and stacking several images, so be it. This is neither an advantage nor a
disadvantage compared with film.

_________________________________________________

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

Talking about Orion - here's a film Orion - a stacked composite. Technique
are the same on software. Well exposed film has a very good range.

Take Care,

JAS


"Chris L Peterson" wrote in message
...
On Wed, 31 Dec 2003 10:08:49 -0800, "Del Johnson" delastro@{right star in
Orion's belt}.sdsu.edu wrote:

Sounds like you are still confusing range with sensitivity.

Not at all. Sensitivity is a whole separate issue, and I'm not discussing
it at
all.


Any single unprocessed CCD of the Orion Nebula that shows the fainter
wisps
will completely burn out the bright core, whereas a film image will do a
better job of capturing the entire dynamics of this object (albeit with a
longer exposure).

You are fooling yourself here. Most film has an overall dynamic range of
about
3A, or maybe 3.5A if you really push out into the extremely non-linear
portion
of the response curve (that is, where a factor of 10 difference in source
intensity produces essentially the same density on the film). Most CCDs
have an
overall dynamic range of about 78dB, or 3.9A, and that is nearly linear
end to
end. The simple fact is that if you make a single CCD exposure of the
Orion
nebula adjusted just to the point where the core is about to saturate, you
will
have captured more detail at the wispy edges than the film image will give
you
assuming that you expose it long enough to compensate for the difference
in
sensitivity.

The trick with film is that you can expose it even longer than that in
order to
bring some of the wispy detail up on the image, and still have a
reasonable
looking core. But even so, that core has been pushed up onto the flat part
of
the response curve, which means that much of the structural detail has
been
obliterated, even if it doesn't have the characteristic blown-out
appearance of
a saturated CCD image.


The only good images of the Orion Nebula with a CCD are
a result of multiple stacked images or mosaics that have been pumped up
with
paint software.

I think this is a bit of an exaggeration, but if not, so what? In what way
is
taking multiple CCD images a problem? There is virtually no difference in
effort
between taking one CCD image or taking several, and the overall exposure
time is
still shorter with the CCD. So if the normal CCD technique involves
collecting
and stacking several images, so be it. This is neither an advantage nor a
disadvantage compared with film.

_________________________________________________

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

On Wed, 31 Dec 2003 20:06:54 GMT, "Jose Suro" wrote:

Talking about Orion - here's a film Orion - a stacked composite. Technique
are the same on software. Well exposed film has a very good range.

No link? But anyway, don't mistake me- I'm not saying that it isn't possible to
get excellent results with film. People have done so for years, and with the
increased use of tricolor filter imaging on B&W film have done even better. It's
just that in a side-by-side comparison between digital and film imaging, I'm
hard pressed to think of any way in which film is better other than cost per
square inch of detector.

_________________________________________________

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

Sorry about the link! I was on the phone and thought I had copied it.

http://astrosurf.com/lorenzi/images/m42.htm

I think 35mm film doesn't have any advantage over CCD other than cost - but
that's a big one. Also, starting with film and moving to CCD is a good way
to get your feet wet before spending the megabucks. Film can't compare with
CCD in sensitivity. I still use it though, because I find the color
saturation of film and the smaller stars appealing.

Happy New Year!

JAS


"Chris L Peterson" wrote in message
...
On Wed, 31 Dec 2003 20:06:54 GMT, "Jose Suro"
wrote:

Talking about Orion - here's a film Orion - a stacked composite.
Technique
are the same on software. Well exposed film has a very good range.

No link? But anyway, don't mistake me- I'm not saying that it isn't
possible to
get excellent results with film. People have done so for years, and with
the
increased use of tricolor filter imaging on B&W film have done even
better. It's
just that in a side-by-side comparison between digital and film imaging,
I'm
hard pressed to think of any way in which film is better other than cost
per
square inch of detector.

_________________________________________________

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