Which focuser fits which telescope?

[ThomasLondon]

This may be a really stupid question, but: How do I find out which focuser fits my telescope (a Skywatcher 102 Startravel)? There is an upgrade from Skywatcher with 1:10 drive, but can I also use others? How do I know which one is the right size - I presume telescope tubes have different diameters?

 

Best

Thomas

[Merlin66]

If you want a direct change over, look for one which has a 96mm diameter fitment.

 

[AdeKing]

I have an ST102 and I'm pretty sure that any focuser suitable for an 80ED will also fit the ST102 as they use the same tube. 

I upgraded mine with the stock dual speed focuser from an ED80. 

As Merlin says anything suitable for a 96mm tube with three fixing screws should fit. 

Ade

 

[John]

As stated above, the inside diameter of the tube is 96mm so thats the focuser fitting to go for. Some focusers have different flanges you buy to fit them to different scope brands / models.

One thing to ensure is that whatever focuser you fit is the right length for the scope, ie: enables eyepieces / cameras to reach focus. It has been known for a nice new focuser to be fitted only to find that accessories that used to come to focus, now don't because the optical length of the focuser unit has changed.

Also, with the fast F/5 focal ratio of the ST102 you need to make sure that the inside end of the focuser drawtube is not intruding into the light path and vignetting the image.

Sorry if thats made things a little more complex.