#1  
Old 12-03-2009, 08:26 PM
desler's Avatar
desler
Registered User

desler is offline
 
Join Date: Jan 2008
Location: Werribee, Australia
Posts: 1,053
Help!

Can someone help me out please????



Ok, Canon Eos 1000D. Ed 80, and dobs 12 and 8 inch.

Here goes, have prime focus adapters and can achieve focus in the ed80 and am very happy. Cannot reach focus in either of the Dobs, I understand why.

Pop a x2 ed barlow (gso) in the ed80 at prime focus, won't reach focus????

Pop same barlow in 12 inch dob with camera at prime, focus (WHAT??????)

Sometimes I feel I've only peeped inside the door of a very long corridor.


I wonder if there's light at the end.


Darren
Reply With Quote
  #2  
Old 12-03-2009, 08:46 PM
peter_4059's Avatar
peter_4059 (Peter)
Big Scopes are Cool

peter_4059 is offline
 
Join Date: Jun 2007
Location: SE Tasmania
Posts: 4,532
Darren,

My experience is you can't get enought inward focuser movement with the dob but the barlow moves the point of focus (out) so you don't need to rack the focuser in as far and can therefore achieve focus.

I suspect with the ED80 you have to rack the focuser out a lot to achieve focus without the barlow and when you use the barlow you don't have enough outward travel. I'm guessing if you put a spacer between the focuser and the barlow on the ED80 you will be able to achieve focus with the barlow as the spacer effectively gives you more outward focuser travel.

Peter
Reply With Quote
  #3  
Old 13-03-2009, 08:36 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Correct. You have to add at least another 80mm to the focuser barrel length to reach focus with a barlow x 2 on the ED80.
Reply With Quote
  #4  
Old 13-03-2009, 09:00 AM
desler's Avatar
desler
Registered User

desler is offline
 
Join Date: Jan 2008
Location: Werribee, Australia
Posts: 1,053
Thanks guys, Spent a fair bit of last night scratching my head!

Is there any other way of reaching focus on the dob, without a barlow?
Does a focal reducer have a similar effect?

Darren
Reply With Quote
  #5  
Old 13-03-2009, 05:57 PM
peter_4059's Avatar
peter_4059 (Peter)
Big Scopes are Cool

peter_4059 is offline
 
Join Date: Jun 2007
Location: SE Tasmania
Posts: 4,532
I'm aware of a couple of options to achieve focus with the dob other than using a barlow:

1 - move the primary mirror forward either with longer collimation bolts or cut an inch or two off the tube.
2 - get a teleview universal parracor.
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 10:10 PM.

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