SV102 focal length issue

[yardstar]

In order to reach the focus point on my SV102ED I have to extend the eyepiece approx 4" away from the end of the telescope. I've owned this scope for years and this is the first ime I've seen this issue. I had it put away for a couple years but no damage during storage. Any ideas would be greatly appreciated.

[Nightspore]

34 minutes ago, yardstar said:

In order to reach the focus point on my SV102ED I have to extend the eyepiece approx 4" away from the end of the telescope. I've owned this scope for years and this is the first ime I've seen this issue. I had it put away for a couple years but no damage during storage. Any ideas would be greatly appreciated.

 

Odd. Are you using a different diagonal to the one you usually use? 100mm seems long for back-focus. What is the eyepiece focal length? Amici prisms have a long light path. So if you're using one it may need more back-focus. Although around a 100mm seems a lot.

 

 

Sometimes I've needed an extension tube with some eyepieces.

 

 

I had to use an extension ring on my 72ED DS Pro when I used a Takahashi prism

 

 

But it only took about 5mm to achieve enough back-focus.

[yardstar]

I'm using a 26mm. The same one I've used in the past. Actually the one I got with the scope. I am completely out of reasons as to why this isn't working. I've used this scope for years. I am not using a diagonal. It just makes no sense. Thnx for responding and if you haver any other thoughts it would be most appreciated..

[Nightspore]

5 minutes ago, yardstar said:

I'm using a 26mm. The same one I've used in the past. Actually the one I got with the scope. I am completely out of reasons as to why this isn't working. I've used this scope for years. I am not using a diagonal. It just makes no sense. Thnx for responding and if you haver any other thoughts it would be most appreciated..

 

If it isn't a mechanical issue with the focuser, which sounds unlikely anyway, it could be with the eyepiece itself. If you have any other eyepieces try those to see if they attain focus as usual. It may be that the objective itself has shifted in some way affecting the collimation. My guess is that the eyepiece is borked in some way. Perhaps a loose lens or lens group?

[yardstar]

Well strangely enough I just installed my diagonal on the scope and it seems to focus fine with the 26mm eyepiece. I don't remember having to put the diagonal on to use to scope but I'm old and it's been almost 5 years since I have used it. Still I think I should be able to just use the eyepiece without the diagonal.

[Nightspore]

1 minute ago, yardstar said:

Well strangely enough I just installed my diagonal on the scope and it seems to focus fine with the 26mm eyepiece. I don't remember having to put the diagonal on to use to scope but I'm old and it's been almost 5 years since I have used it. Still I think I should be able to just use the eyepiece without the diagonal.

 

Technically you should be able to use just the eyepiece. It can depend on the EP focal length and the focal ratio of the scope. It's not unusual to have back-focus or in-focus problems with varying and different combinations of eyepieces and diagonals though.

 

 

I could have in-focus problems with some EP's with the Long Perng aftermarket focuser on my ST102.

 

 

After replacing it with a MoonLite, which has a very long drawtube by design and yet is short and compact, I had no more issues. The scope is f/4.9.

 

 

The Long Perng focuser has no focusing problems with my f/7.5 80ED DS Pro.

[yardstar]

Thanks for responding. Like I said it's been awhile and since I've ran the scope. I put the diagonal on and  focusing seems to be cured. Tonight I'll set up outside and test my camera to see if all is well. Growin old aint for sissys.  

[Nightspore]

You're welcome.

[TerryMcK]

The original poster hasn’t come back for more than 3 months so possibly won’t see any replies.