ICEINSPACE
Most Read Articles
Moon Phase
CURRENT MOON Waxing Gibbous
99.3%
The Sun Now
Time Zones
Sydney*
10:51 am
Perth
7:51 am
Auckland*
12:51 pm
New York
6:51 pm
Paris
12:51 am
GMT
11:51 pm




  #1  
Old 06-09-2018, 06:04 AM
Lee's Avatar
Lee
Colour is over-rated

Lee is offline
 
Join Date: Sep 2005
Location: Newcastle, Australia
Posts: 2,414
Optical aberration in OAG

Another 'image' from last night.... unfortunately not much from the big end of the scope. This is something I've noted before in the PHD window.

Scope is 8" f/4 Bintel Newt. OAG and lodestar.

Is this astigmatism? - it has never seemed to bother PHD much, but I suspect it is an amplified version of what is happening in the main CCD.....
Attached Thumbnails
Click for full-size image (starshapes.jpg)
29.3 KB38 views
Reply With Quote
  #2  
Old 06-09-2018, 06:34 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 17,459
Quote:
Originally Posted by Lee View Post
Another 'image' from last night.... unfortunately not much from the big end of the scope. This is something I've noted before in the PHD window.

Scope is 8" f/4 Bintel Newt. OAG and lodestar.

Is this astigmatism? - it has never seemed to bother PHD much, but I suspect it is an amplified version of what is happening in the main CCD.....

A bit of astigmatism mixed with coma. That's pretty standard on the edge of the field of a fast newt. Coma can be dealt with by spacing the corrector, astigmatism by rotating the primary mirror. PHD doesn't care.
Reply With Quote
  #3  
Old 06-09-2018, 07:17 AM
Lee's Avatar
Lee
Colour is over-rated

Lee is offline
 
Join Date: Sep 2005
Location: Newcastle, Australia
Posts: 2,414
Thanks, I suspected similar.... as far as I can tell the MPCC is spaced correctly. I cleaned both mirrors on the weekend and reinstalled/collimated on the bench and then touched up after mounted (not much variation). Of course then the imaging train goes on with whatever tilt is carries?

I took some 1s exposures in a busy star field to try and assess the optical train hopefully ignoring most guiding effects. Guiding last night was pretty 'interesting' though.

This image is a single 1s sub, stretched very hard to see the stars of course. I've added the corners and centre if it helps.

Link to FITS

Thanks for any advice/analysis.... to be honest I've seen worse from this scope, but I've also seen better, and I refuse to believe I can't have round stars across the small 428EX chip.
Attached Thumbnails
Click for full-size image (centre.jpg)
111.4 KB15 views
Click for full-size image (bottom-left.jpg)
73.7 KB15 views
Click for full-size image (bottom-right.jpg)
68.6 KB11 views
Click for full-size image (top-left.jpg)
56.2 KB12 views
Click for full-size image (top-right.jpg)
78.9 KB10 views
Click for full-size image (ngc6637-1s-full-sm.jpg)
96.9 KB11 views
Reply With Quote
  #4  
Old 06-09-2018, 07:42 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 17,459
The field is flat and very well corrected. Just one thing to note is the star shapes. They seem to have 6 spikes like a 3 vane spider. Your newt has 4 right?
Reply With Quote
  #5  
Old 06-09-2018, 07:51 AM
Lee's Avatar
Lee
Colour is over-rated

Lee is offline
 
Join Date: Sep 2005
Location: Newcastle, Australia
Posts: 2,414
Yes, 4 vane spider. I saw the 6 spikes, I'm normally not stretching images as hard, I thought it might be artefact from that.


I'm actually quite impressed at what it picked up in 1s..... which is why I want to get this scope tamed....
Reply With Quote
  #6  
Old 06-09-2018, 08:01 AM
Lee's Avatar
Lee
Colour is over-rated

Lee is offline
 
Join Date: Sep 2005
Location: Newcastle, Australia
Posts: 2,414
Quote:
Originally Posted by multiweb View Post
The field is flat and very well corrected. Just one thing to note is the star shapes. They seem to have 6 spikes like a 3 vane spider. Your newt has 4 right?

I think the stars look oval, worst top left/bottom right, and pretty good bottom left. Tilt? I was too tired to put it through CCD inspector last night, I'll hopefully have time at lunch today.
Reply With Quote
  #7  
Old 06-09-2018, 08:04 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 17,459
Quote:
Originally Posted by Lee View Post
I think the stars look oval, worst top left/bottom right, and pretty good bottom left. Tilt? I was too tired to put it through CCD inspector last night, I'll hopefully have time at lunch today.
I ran your fit through CCD inspector. Collimation is very good, the field is incredibly flat for a fast new, quite surprising actually and there is a slight tilt but it's not something you would even detect visually. The only concern is those 6 spiked stars. Maybe the secondary is stressed or the primary clips. Something is pulling on the glass somewhere. Easily fixed.
Reply With Quote
  #8  
Old 06-09-2018, 08:18 AM
Lee's Avatar
Lee
Colour is over-rated

Lee is offline
 
Join Date: Sep 2005
Location: Newcastle, Australia
Posts: 2,414
I'm happy to read something looks good!

When I reassembled on the weekend, I was careful to get the secondary rotated well - could it be too tight?
The only change I made was I reduced the primary mirror tendency for lateral movement by slipping some plastic shims (approx 0.5mm thick from packaging) between the cork pads and the sides of the mirror. Not tightly, and in fact the mirror could still move (just), just not clunking from side to side when rotated.....
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 09:51 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
OzScopes Authorised Dealer
Advertisement
Interest Free Finance
Advertisement
NexDome Observatories
Advertisement
SkyWatcher 2018 Catalogue
Advertisement
SkyWatcher WiFi Adaptor
Advertisement
FLI Cameras and Imaging Accessories
Advertisement
Lunatico Astronomical
Advertisement
Astronomy and Electronics Centre
Advertisement