Image of the day

Captured by
Mark Eby

M51 Whirlpool Galaxy

My Account

New to Astromart?

Register an account...

Need Help?

Buying a used SCT

Started by WA4HND, 07/20/2008 08:26AM
Posted 07/20/2008 08:26AM Opening Post
Getting ready to look at buying a used SCT... ( C-14 ). Does anyone have any tips on things to look for when checking the scope out. I'd like to have a C dealer I know check it out but not sure how to right up a contract saying sale pending, pending check out.

Any ideas ?
Posted 07/20/2008 11:42AM #1
Things to look for:

Visual inspection:
- Dents, dings, bad scrapes on exterior. Might indicate rough
handling. Though in a large scope like this a few small paint
chips are probably unavoidable.
- Chips, cracksm scratches on glass. Be sure to check around the
- If you look at the reflection off the large lens at the
front, it should have a uniform coloration (probably
light or dark blue). There should not be patches of a
different color.
- Focus knob should turn smoothly with no binding or jumps.
The large mirror should move very slowly when you turn the knob.
- Screw heads should be "clean" with little or no metal
deformation from in-expert disassembly.
- Secondary mirror assembly at the center of the big
lens should not be loose.
- Check for excessive dust or fog on the optical
surfaces. Some dust will be unavoidable. Reflections
off the mirrors should look bright and clear.
- There should not be any paint scrapes or chips inside the
tube. Or loose nuts or screws rolling around inside.
Would indicate some bad problem in the past.

If you can test the scope at night, look at a star
nearly overhead, and perform a "star test" looking at the
image on both sides of focus -- images on either side
of focus should be nearly identical. But problems
from temperature changes and air currents can make
testing difficult. You may need to wait for a night
with good "seeing" and leave the telescope outside
for several hours before testing. This is a very large
subject and probably difficult for beginners.
Star images should look crisp at best focus, assuming
you have very good seeing.

Also check that the image does not shift or jump much
when you turn the focus knob back and forth. If you
looked at Jupiter and adjust the focus, Jupiter should
not move more than about its diameter when you turn the
focus back and forth.

As for having a C dealer check it out, this is probably
a good idea. You could have the seller ship it directly
there. You just need to have a clear agreement with the
seller on return policy if it does not check out. How
long does "inspection" period last? Who pays return
shipping, etc.

Be sure to understand who is responsible for
shipping damage, say if it were damaged on way to or
from the C dealer and shipping company refuses
to cover it (claims poor packing, etc.).