Dr E D F Williams wrote: > > JC, > > I wish my 400mm Sigma APO produced results as sharp! > > If by mirror lens you mean something made specifically as a telephoto for > terrestrial photography then your aversion to them may be justified. But > consider the two Questars - 3.5" and 7". > These are far superior to any telephoto that has ever been offered for > sale to the public.
This statement is without dispute. Questar hand figures their optics as individual sets, for each and every instrument they build, to _exceed_ the usually recognized standards or 'limits' of astronomical telescope resolution. I know of no telescope available to the general public, as Don indicates, that is made to such exacting criteria. I once had a 3.5" Questar, and it was so good, I was able to pick up on the vibrations from cars passing by and others walking thru the house... I had a very stout and stiff tripod, but it was the floor the tripod was sitting on that was my problem. With other telescopes, you couldn't notice it, mainly bacause you were power limited. Crank up the power and very soon the image starts deteriorating badly, but with the Questar, you could actually USE the power, if you could view thru the eyepiece without touching the mount or instrument in any way! <grin> Lovely instruments, with a price to match... keith whaley > Every time you > see the launch of the space shuttle on TV its been taken though a 7" Questar > specially adapted for the job - or so I've read anyway. I used the small one > in my laboratory and sometimes out in the field. I have none of those > slides, but I'm sure there are samples to be seen on the Questar web site. > > However, if you want sharp pictures with a Questar, or any really long > telephoto for that matter, you need to go to extraordinary, and tiresome, > lengths to get sharp pictures at high magnification. All the precautions > used in photomicrography have to be applied. In a nutshell - as long as > there is direct physical connection between the camera and the optics, half > the battle is won. However, each part can be fastened to the same vibration > free base. The shutter should either be replaced by an external one, or the > exposure should be long - or very short indeed. > > Don
