Testing the resolving power of a telescope?

Hi ppl

I was just wandering if it is possible to do a ground-based test of
the resolving power of a telescope. With ground-based I mean you look
at a target on earth, to exclude seeiing. I tought on something like
http://www.efg2.com/Lab/ImageProcess...s/Image133.gif
placed some 20-30 meters away or so.
Would this work for a telescope test?

Thanks for your help!
Pieter

I've used those targets to test many camera lenses and they are very good if
you follow the instructions. The problem I ran into was the distances required
for a 3 meter focal length scope. I just couldn't get far enough away. Under
these conditions your testing at closest distance rather than at infinity.
Scopes are designed for flat to flat separated at an distance of infinity.

There are higher quality versions of this test target on the Web.
Google the search terms USAF resolution download, etc. You might want
to also download a postscript (PS) version or PDF. Print out on a
decent laser printer.

I've done a fair bit of resolution testing for camera lenses and none
for scopes. I imagine that you may run into problems if you conduct
your tests on bright sunny days which heats up the pavement and causes
"seeing" problems.

Many Leica lens users will say that resolution tests don't really tell
you much about a camera lens' performance on actual subjects.
Qualities such contrast, colour accuracy, distortion, saturation and
bokeh are not something that can be measured or defy quantification in
a USAF test, at least for folks who lack lab grade test bench
equipment. Mixed all that up with telescope eyepiece performance and
visual versus photographic resolution and what does it all mean? As
such, I'm not sure if resolution testing would tell me much about my
scope's performance for stellar objects (assuming this is what we're
mostly using the scope for).

Being new to star gazing, I thought the best way to test one's scope
is to split doubles or bring it to a star party and compare. My $.02

S&B




(Pieter Tieghem) wrote in message . com...
Hi ppl

I was just wandering if it is possible to do a ground-based test of
the resolving power of a telescope. With ground-based I mean you look
at a target on earth, to exclude seeiing. I tought on something like
http://www.efg2.com/Lab/ImageProcess...s/Image133.gif
placed some 20-30 meters away or so.
Would this work for a telescope test?

Thanks for your help!
Pieter

Many Leica lens users will say that resolution tests don't really tell
you much about a camera lens'

Your not kidding. When I reported results for peoples Lica lenses did I
get a lot of flack. Some of the old time lenses like those for the Speed or
Crown Graphics were superb in these tests.
This is essentially a contrast test and as such I think its usefull for
astronmy. In the actual tests these targets are spread across the entire field
of view so that problems like coma are readily apparent.