Cant get focus.

[Robindonne]

I have a problem with a small refractor.  When my camera is mounted and the focustube is at max outward, i still need more length.  So i quess thats where the extension tubes come in.  But what happens if i go for a focal reducer?  Does it bring me in focus faster? I mean shorter?   So instead of an extension tube for the needed length, go for a focal reducer?   If anyone can keep me off of buying a reducer then im happy to hear.   Thx

edit.  Its a 71 mm zenithstar.  And because im still in doubt to get an oag, will the thickness of the oag help me get in focus?

Edited May 22, 2020 by Robindonne

[Davey-T]

Focal reducer may only make a few millimetres difference, the scope is designed to use a diagonal which adds the extra light path so something like a  50mm extension should get you back to normal.

Dave

[Robindonne]

I stole a picture from another thread with the same scope.  The person has indeed a small extension for it.
So if the reducer just shorten the needed length by a couple of mm’s an extender is the option to go.  
 But based on planning to use an oag, is it an idea to look for a thick oag and solve both problems with one device?   

[Davey-T]

Bit overkill using an OAG a small guide scope might be better.

Dave

[Robindonne]

17 minutes ago, Davey-T said:

Bit overkill using an OAG a small guide scope might be better.

Dave

Hmm ok.  I asked a related question some days ago here.  And the answers were mixed about the oag assembly switching from one to another scope.  But would you still say its overkill if i can use it on multiple scopes?   

[Davey-T]

The one in that picture looks like its got a WO flattener reducer which gives the right spacing for a DSLR it is a good thing to have for imaging and leaves no room for an OAG.

With all the faffing about getting spacing right for an OAG you probably wouldn't want to be swopping it around, they're better suited to long focal length scopes, a guide scope would be a better investment and really easy to swop between scopes.

Dave

[Robindonne]

Ok thx very much

[Alien 13]

5 hours ago, Robindonne said:

I stole a picture from another thread with the same scope.  The person has indeed a small extension for it.
So if the reducer just shorten the needed length by a couple of mm’s an extender is the option to go.  
 But based on planning to use an oag, is it an idea to look for a thick oag and solve both problems with one device?   

Lol thats me in my Star Wars gown. The scope needs a two inch extension if using it without a FR/FF but none is required when using one.. There is no extension in use in that picture, its just that the FF/FR has been pulled out a bit to hit the end stop of the undercut.

Alan

Edited May 22, 2020 by Alien 13

[Robindonne]

18 minutes ago, Alien 13 said:

Lol thats me in my Star Wars gown

That or some russian tsar was what i thought.   But when i use a reducer im good to go?   That makes it easy to search for the solution.  Of course a big thx for the info and sorry for the copyright thing.  

[Alien 13]

6 minutes ago, Robindonne said:

That or some russian tsar was what i thought.   But when i use a reducer im good to go?   That makes it easy to search for the solution.  Of course a big thx for the info and sorry for the copyright thing.  

No problem, any images I post are free to use by anyone..

Alan

[Shimrod]

15 hours ago, Davey-T said:

With all the faffing about getting spacing right for an OAG you probably wouldn't want to be swopping it around, they're better suited to long focal length scopes, a guide scope would be a better investment and really easy to swop between scopes.

Dave

Wouldn't that depend on the scopes - I don't do any guided imaging yet, but from reading I thought a guidescope with 150mm focal length would not be suitable for an SCT with 2000mm focal length. Conversely, a 600mm guidescope would provide mounting challenges if used with a small refractor. Is there a 'goldilocks' guidescope that would work with both small refractor and SCT?

[Davey-T]

1 hour ago, Shimrod said:

Wouldn't that depend on the scopes - I don't do any guided imaging yet, but from reading I thought a guidescope with 150mm focal length would not be suitable for an SCT with 2000mm focal length. Conversely, a 600mm guidescope would provide mounting challenges if used with a small refractor. Is there a 'goldilocks' guidescope that would work with both small refractor and SCT?

Wouldn't put too much faith in the mathematical theory, over the years I've guided my SCT with 80mm f/9, 50mm f/4, 100mm f/6, 80mm f4.9, OAG and anything else that came to hand and all worked ok.

A "normal" guide scope will work with most scopes.

Dave