Digital camera vs. digital SLR

Several people have been talking about digital SLRs (Canon, etc.) here
lately, and I wanted to point out an advantage of conventional (non-SLR)
digital cameras: No vibration. As I understand it, the digital SLR mirror
makes just as much of a "flap" as the mirror in a conventional SLR. This
negates the main advantage of the digital camera, which is that it does not
shake the telescope.

One of the main things I'd look for in a fixed-lens digital camera is a
large entrance pupil, i.e., a large-diameter lens opening. (Look into it
and see; don't judge it by the size of the glass.) With a large entrance
pupil, you can use a wider range of eyepieces successfully.

--
Clear skies,

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

"John Steinberg" wrote in message
...
Michael A. Covington:

Several people have been talking about digital SLRs (Canon, etc.)
here lately, and I wanted to point out an advantage of conventional
(non-SLR) digital cameras: No vibration.

Not true, at least not universally. Both my Nikon Coolpix 950 & 995 do
experience some vibration. The shutter may be electromechanical but
they are not free from vibration. You can even feel the vibration of
the camera body should you opt for auto-focus.

Well, "no vibration" was an exaggeration, but it's orders of magnitude less
than an SLR.

I use a Coolpix 990 and only wish it had a wider entrance pupil (although
3.5mm, or whatever it is, is not bad).

Michael A. Covington wrote:

Well, "no vibration" was an exaggeration, but it's orders of magnitude
less
than an SLR.

Canon EOS DSLRs (D30,D60, 10D, 1Ds) allow "mirror lock-up" to be quickly
enabled/disabled.... zero slap!

(example image):

http://www.astro-nut.com/m45.html


I use a Coolpix 990 and only wish it had a wider entrance pupil (although
3.5mm, or whatever it is, is not bad).

Be careful what you wish for... the smaller CoolPix lenses help overcome
vignetting!

When using a non-SLR digicam (ie: most consumer grade models with
permanently attached lenses), vignetting seems to be far less a problem with
those using smaller diameter lens assemblies. Vignetting with afocal setups
can be further reduced or eliminated by using the camera's *optical zoom*
(never the digital zoom, which reduces effective resolution) and an
appropriate fl eyepiece.

Their instantaneous feedback and ease of use, make digicams and DSLRs sure
winners for many astro-imagers. One need no longer toil with the
mathematical calculations used to determine EFR and exposure settings and
then hope the kid at foto-mart gets the developing right (ooops!)... simply
take the shot and look at the image or its histogram! If it isn't AOK, you
can make corrections and try again... no fuss, no muss, no waiting! Ya' just
gotta' love it! )

A good resource for those intrigued with the prospect of digicam
astro-imaging is the Digital Astro egroup:

http://groups.yahoo.com/group/digital_astro/

and the FAQs pages:

http://www.szykman.com/Astro/AstroDigiCamFAQ.html

Cheers,

Paul

--- http://www.astro-nut.com ---

"John Steinberg" wrote in message
...
snip
A threaded lens cell is also an assist, and although evidently no
longer a popular marketing tool, the pivoting body of some of the
Nikons and Casio models provided excellent ergonomic benefits for the
astro (and non-astro) user.

I totally agree. Being able to screw my Casio (or Canon if you have one)
directly to a scopetronix 2" eye piece comes in real handy and solid, as
well as being able to use extra lenses/filters for non-astro stuff.

Jim

"Paul Hyndman" wrote in message
.. .

I use a Coolpix 990 and only wish it had a wider entrance pupil
(although
3.5mm, or whatever it is, is not bad).

Be careful what you wish for... the smaller CoolPix lenses help overcome
vignetting!

When using a non-SLR digicam (ie: most consumer grade models with
permanently attached lenses), vignetting seems to be far less a problem
with
those using smaller diameter lens assemblies. Vignetting with afocal
setups
can be further reduced or eliminated by using the camera's *optical zoom*
(never the digital zoom, which reduces effective resolution) and an
appropriate fl eyepiece.

If that is true, it's not due to small diameter. It's due to having the
entrance pupil closer to the front of the lens assembly.

An entrance pupil smaller than the exit pupil of the eyepiece prevents you
from using the full aperture of the telescope.

Be careful what you wish for... the smaller CoolPix lenses help overcome
vignetting!

When using a non-SLR digicam (ie: most consumer grade models with
permanently attached lenses), vignetting seems to be far less a problem with
those using smaller diameter lens assemblies. Vignetting with afocal setups
can be further reduced or eliminated by using the camera's *optical zoom*
(never the digital zoom, which reduces effective resolution) and an
appropriate fl eyepiece.


My experience as well. I think this is one of the reasons that the CoolPix are
so popular for "digiscoping." The two digital cameras I have both use large
pixel arrays and when used with even 4.7 mm exit pupil (Pronto with a 32) will
produce serious vignetting unless zoomed in significantly.

I mostly use this combination for photos of wild birds so the vignetting really
is a problem. Zooming in does help but also makes everything more sensitive to
vibration and of course often is not the desired photo anyway.

A sharp focus and vibration are the big issues here because one has to focus
carefully for each bird and one needs to do so very quickly because those
birdies have a nice habit of flying away. For me this means using a solid
tripod, setting the camera on infinity, focusing the scope with my distance
glasses on and then hand holding the camera to the eyepiece. I have gotten
some very nice long shots that were very sharp, but often the focus is just
off.

Adapters that hold the camera to the eyepiece seem nice but must be removed to
get that good sharp focus at the eyepiece. By the time the camera is aligned
and ready for the shot valuable time has been lost and the skittish subject
will likely be gone.

A bit OT but the reality I think is that when selecting a digital camera for
afocal use one really wants a camera with small pixels and small sized short
focal length optics that can utilize small exit pupils.

Jon Isaacs