#1  
Old 25-07-2021, 09:54 PM
Greggles (Gregory)
Registered User

Greggles is offline
 
Join Date: Aug 2017
Location: Sydney, Australia
Posts: 63
Pinched optics?

Hi All,

Recently cleaned by 10" Dobsonian mirror and took the scope out for the first time tonight.

Quick question, collimation is not perfect but is this pinched optics or just the clips visible when completely out of focus? For the life of me I cant remember if i could always see the clips or not.
Photos attached. in focus still looking pretty good when imaging a star.

On a side note, cleaning went pretty well.. i think.. some streaking on the mirror despite being rinsed with demineralized water, but i''ve heard that's not an issue.

pretty terrible seeing here in Sydney tonight but iI pointed the scope to a low Saturn and it was the worst that i've ever seen. Hope its the seeing and not the optics.

Cheers

Greg
Attached Thumbnails
Click for full-size image (DSC_0208 -2.jpg)
283.0 KB49 views
Click for full-size image (DSC_0189 - 2.jpg)
280.9 KB52 views
Click for full-size image (DSC_0191.jpg)
203.9 KB57 views
Reply With Quote
  #2  
Old 25-07-2021, 09:59 PM
mswhin63's Avatar
mswhin63 (Malcolm)
Registered User

mswhin63 is offline
 
Join Date: May 2009
Location: Para Hills, South Australia
Posts: 3,575
Need a corrector for vignetting to suit your camera and scope combination.
Reply With Quote
  #3  
Old 25-07-2021, 10:20 PM
Greggles (Gregory)
Registered User

Greggles is offline
 
Join Date: Aug 2017
Location: Sydney, Australia
Posts: 63
Quote:
Originally Posted by mswhin63 View Post
Need a corrector for vignetting to suit your camera and scope combination.
Yep agreed been contemplating it for a while. Quite happy with my level of imaging with a dobsonian, not sure if I should get one. Also think it will effect my focus and I've already had to move the mirror up to get focus with my DSLR.

Any thoughts about the pinched optics regarding clips visible when out of focus?
Reply With Quote
  #4  
Old 25-07-2021, 11:58 PM
Saturnine (Jeff)
Registered User

Saturnine is offline
 
Join Date: Jul 2008
Location: Wollongong
Posts: 1,665
The seeing is terrible tonight, whenever we have strong westerly winds it's almost a given.
The 3 notches you see are the shadows of the mirror clips and nothing to be concerned about. The optics do not seem to be pinched, usually shows as a triangular out of focus star test image. Google pinched optics and check the images of the different aberrations presented as examples.
Your collimation is slightly out as the secondary shadow is slightly off centre, a bit of fine tuning will sort that out.
Reply With Quote
  #5  
Old 26-07-2021, 12:27 AM
Greggles (Gregory)
Registered User

Greggles is offline
 
Join Date: Aug 2017
Location: Sydney, Australia
Posts: 63
Thanks Jeff for the confirmation.

Yep my laser collimator is not perfect was planning on fixing collimation tonight but clouds set in before I had a chance to do anything.

Ehhhh the Sydney weather has been so bad lately I was desperate to get out tonight.

Quote:
Originally Posted by Saturnine View Post
The seeing is terrible tonight, whenever we have strong westerly winds it's almost a given.
The 3 notches you see are the shadows of the mirror clips and nothing to be concerned about. The optics do not seem to be pinched, usually shows as a triangular out of focus star test image. Google pinched optics and check the images of the different aberrations presented as examples.
Your collimation is slightly out as the secondary shadow is slightly off centre, a bit of fine tuning will sort that out.
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 10:17 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
Advertisement
Limpet Controller
Advertisement
Testar
Advertisement
Bintel
Advertisement
NexDome Observatories
Advertisement
Astronomy and Electronics Centre
Advertisement