Viewing by eye versus astrophotography

Peter Webb wrote:

I note some excellent photos were taken on a 85 mm aperture refractor.
Somebody in a telescope shop recommended a refractor - I never really
considered them - is there something special about refractors and
astrophotography ?



Newtonians give the most bang for the buck, Apo refractors give the most
bang for the aperture, and require less maintenance, but they also cost
the most.

The lack of a central obstruction helps improve contrast. You can get a
feel for it by holding your thumb up at arms length and looking at
something in the distance. You can see "behind" your thumb but your
thumb is also there to add confusion.

Maintenance on a reflector includes periodic collimation, and infrequent
re-silvering of the mirrors.

The largest "portable" refractor I've seen is a TMB 229 owned by a
friend. The views are glorious, but you really need at least two people
to set it up, and three or four is better. A couple friends have 10"
newtonians they can easily transport and set up by themselves.

On Thu, 09 Oct 2008 10:57:39 -0400, "Mark S. Holden"
wrote:

The lack of a central obstruction helps improve contrast.

However, this is pretty much a non-issue if you're using the scope for
imaging. Most of the premiere imaging instruments in the world (and out
of it, since this includes the Hubble) have very large central
obstructions. Furthermore, when used visually, the contrast effects of
the central obstruction are only relevant to lunar and planetary
observing. The eye's visual acuity is too low when viewing dim objects
to come close to being affected by the effects of the CO on the systems
MTF.
_________________________________________________

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