Re: Starfields from "bulb" and RAW?

grant keaton wrote:

Correct. I'd only change that last sentence to:

"Just boost the ISO, and/or use longer shutter speeds, and/or possibly stack
images."

When going for any camera, don't forget the importance of aperture too (you
being an amateur astronomer knows all about it though). That's the nice part
about the super-zoom P&S cameras, often having apertures 1 to 3 stops larger
than the same partial range focal-lengths in DSLR zoom lenses.

This is incorrect! The are two major factors at work ere:
1) Aperture (not f/stop). A 50mm f/2 lens on a DSLR has a 25 mm aperture.
On a P&S camera, where the crop factor may be 4x or larger, that same
50 mm equivalent is really a 12.5mm or shorter focal length. The aperture
on a 12.5mm FL f/2 lens is only 6.25 mm. The larger actial aperture on the
DSLR collects more light (16x).
2) The larger the pixels, to more light each pixel collects. An f/2
lens on every format camera delivers surface brightness the same
(e.g. expressed in photons/square micron) so a larger pixel with
more surface area (more square microns) collects more light.
The difference between the smallest pixel P&S and large pixel DSLRs
is 12 to 16x and larger. This difference is expressed in the
"Unity Gain ISO" in Figure 6 at:
http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary

In the small pixel cameras, with unity gain near or below ISO 100,
when you boost ISO above 100, would largely just boost noise as much as
signal, so there is little to no actual gain in detecting fainter
subjects. Not true with the large pixel DSLRs: boosting ISO
detects fainter subjects.

All of the cameras you are considering will be fine.

Determine the pixel size. That determines fundamental
light collection. A low end 6-megapixel DSLR would do FAR better
at low light work.

Any camera is, in the right
hands. It's just going to be a matter of deciding which of their strengths is
the highest priorities for you and learning how to implement their strengths for
your intended purposes. If you plan on doing stacked-frames don't ignore
intervalometer options or being able to remotely control it by computer. I don't
know if any of those you are considering have those options. This then is where
one of the earlier Canon P&S models supported by CHDK can help. Doing what no
other camera can do unless tethered to a computer to control it. Personally, for
low-light, indoor, I'd go with the Fuji. But danged if that new FZ18 isn't
putting out some impressive photos, some results I've seen from it being better
than top-line DSLR+L-glass images.

Basic physics says this can't be true for low light work, and is
highly doubtful in any situation.

(other great info snipped)

Roger
.

Relevant Pages

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