Go Back   IceInSpace > Beginners Start Here > Beginners Talk

Reply
 
Thread Tools Rate Thread
  #1  
Old 16-10-2021, 10:43 PM
Auspecial
Registered User

Auspecial is offline
 
Join Date: Feb 2016
Location: Sydney
Posts: 23
Eyepiece focus with an RC8.

Hello all, I recenly purchased a GSO RC8 and have been having good fun learning to do astrophotography but I also bought a 26mm 2" eyepiece and cant seem to find focus. I have zero experience with visual astronomy. Do eyepieces focus at the same point as a camera? Is there any way to work out where the focus point will be on a GSO RC8 for an eyepiece?


Cheers!
Reply With Quote
  #2  
Old 16-10-2021, 11:02 PM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 1,495
No, they don't. Typically you'll need to use some extension tubes to get the eyepiece far enough away. Mine uses large rings that screw in between the telescope and the focuser, so the focuser assembly sits about another 5 inches away from its normal position.


Markus
Reply With Quote
  #3  
Old 17-10-2021, 12:23 PM
Auspecial
Registered User

Auspecial is offline
 
Join Date: Feb 2016
Location: Sydney
Posts: 23
okay great thanks mate
Reply With Quote
  #4  
Old 17-10-2021, 12:55 PM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 1,495
Quote:
Originally Posted by Auspecial View Post
okay great thanks mate
Wait, sorry, I think I have that the wrong way round. The EP needs to be *closer to the telescope than the camera. It's the camera that uses extension tubes. Are there any bits that unscrew?
Reply With Quote
  #5  
Old 18-10-2021, 07:51 AM
Auspecial
Registered User

Auspecial is offline
 
Join Date: Feb 2016
Location: Sydney
Posts: 23
I used it with all of my big extension tubes and the focuser and couldnt get focus, then used it with zero extension tubes just the focuser and still couldn't find focus. Not really sure where to go from here
Reply With Quote
  #6  
Old 18-10-2021, 09:41 AM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 1,495
If you point it at the moon, then hold a piece of paper in front of the (empty) focuser you can measure the scope's focal plane, where the camera would sit and go from there.



Also if there is not enough backfocus, you could try insering a Powermate to move the native focus out a bit.


Markus
Reply With Quote
  #7  
Old 18-10-2021, 01:28 PM
Auspecial
Registered User

Auspecial is offline
 
Join Date: Feb 2016
Location: Sydney
Posts: 23
great thanks for the tips mate appreciate it
Reply With Quote
  #8  
Old 18-10-2021, 01:54 PM
N1 (Mirko)
Registered User

N1 is offline
 
Join Date: Oct 2013
Location: Dunners Nu Zulland
Posts: 1,662
Eyepieces generally sit further from the objective than cameras*. Start with the focuser screwed directly to the tube. Point the telescope at a bright star, wind the focuser all the way in, put the eyepiece in then start racking out the focuser and observe the donut formed by the defocused star. If it's getting smaller, you're on the right track. If you hit the end before things are sharp, add extensions (or a diagonal). If you see no donut to begin with even after making sure it's pointed at the star, add one of the two M90 25mm extension rings, or a 2" extension before the eyepiece and restart the process as above.

If, however you are still too far out even with no extensions or diagonal in the path, and the focuser all the way in (i.e. donut gets bigger as you rack out from there), then I suspect your mirrors are not at the correct spacing from each other. That's very unlikely though, especially if the RC is new and your cameras focus fine*. But if that's the problem you'll want to get that fixed because the distance between primary and secondary is absolutely critical in RCTs. Beforeyou do anything like that, you must read up on the subject or it will become a major headache.

*More simply, you could establish roughly where the camera's senor comes to focus, and move out from there. The EP should focus a few to a few dozen mm behind that spot, depending on its design.

Last edited by N1; 18-10-2021 at 02:13 PM.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:36 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
Testar
Advertisement