Buying secondhand - how to test telescope...?

[Saturnalia]

I have my eyes on a TAL 100R (100mm refractor) secondhand and wondered if there are some easy tests I can do to check the optics and so on before I part with my cash...?

I have done a bit of searching here and can't find anything related to this - apologies if I have missed it.

I will almost certainly be viewing the telescope during daytime so it may be difficult to test it on the sky.

Thanks for any suggestions.

[Peter Drew]

Hello Saturnalia. I can't believe that there's been no reply to your post yet so I'll start the ball rolling. In general, it's difficult to exhaustively test a telescope, particularly in daylight without a fair bit of experience. However, with a Tal 100R or other quality refractor you can be pretty confident that if the view looks OK in the daytime it will be at least as good at night. At this stage have a look at the front objective(lens) to make sure that there are no obvious defects such as scratches, scuffed coatings or bad stainings. Minor issues like a little dust or hard to see very fine scratches will not affect the overall performance, remember, this is a used item. Any other future considerations like cleaning or collimation can easily be remedied through this forum.

[Saturnalia]

Thanks for the reply Peter - I was surprised at the lack of responses.

I have had a search here and can find nothing about what to look out for when buying secondhand (especially as an inexperienced telescope owner), I will give it a good look over and carefully examine the lenses, eyepieces and tripod/mount.

Maybe the subject is too broad as I'm sure there are different things to look for depending on the type of 'scope involved - Refractor, Reflector, SCT etc.

Cheers

[Astro_Baby]

I did put a reply up about reflectors but then I reread your post and realised you were talking 'fracs so discarded my original post.

[SpookyKatt]

Hi Saturnalia,

In the case of a Tal 100R I'd check the focuser movement and if its one of

early models with the metal dew shield I'd check the focuser tube to see

if its loose (even if it was though I wouldn't say it was a big deal).

Then I'd look down the tube from the objective end and shine a torch and check

the baffles to make sure none of them are knocked out of place (unlikely

but worth checking). Other than that I would check the primary lens just to

see that it looks ok but other than that I can't think of anything else to check.

Try and see it setup if possible so you can try the mount movement but

if you can't get that just check the tripod and mount as well as the diagonal

and eyepieces etc.

Kathleen

[Saturnalia]

Thanks for that Kathleen - I will take a torch with me...good tip.

[MartinB]

If you can get your hands on a copy the latest edition of AstronomyNow you will find an excellent article by Neil English comparing the optics of a TalR with the newer TalRS. He shows how to check for astigmatism, coma and spherical aberation. Not sure how you do a daytime check for coma and astigmatism though. Neil tested spherical aberration by making 2 masks - 1 covered the central part of the objective and the other the outer part. He checked how much he had to adjust the focus when changing from one mask to the other.

His conclusions were that the optics on the TalR were superb, better than the RS. There were a few internal reflections on with the TalR and the focuser lacked travel and couldn't accommodate 2" EPs.

These scopes are very well built so if there is no evidence of serious abuse it is unlikely that there will be a problem with the optics. From all I've heard the Tal is an excellent scope

[Saturnalia]

Thanks Martin - my first time dealing with a Sub Giant...

I think I may have found that here:

A Little Piece of Russian Magic - Review

[barkis]

I have never heard of any criticism of Tal, except the odd hardware niggle. The optics are generally well respected.

Perhaps the seller will let you evaluate the telescope over a couple of days, a deposit may suffice to encourage him/her to do this.

It would help if you were both geographically close.

I would bet you will be happy with the unit.

Ron.

[Saturnalia]

Thanks for the encouragement Ron - I will give it a good look over and go from there...isn't the human eye capable of accuracy to around 1/1000"...if so, I should be fine...!