#1  
Old 30-09-2014, 08:49 AM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,311
Sub Star tails causes?

I find that if I go to ten minute subs I get very short star tails, what can cause this?

Background to question:

8" imaging newt, Canon 450D, 60mm guidescope and ASI130mm guide camera, running Metaguide; mount is NEQ6Pro (fairly new one), polar aligned before starting at 0' 0" both alt and az. Baader MPCC Mark III Coma Corrector

Example, imaging NGC55 at a dark site (Bretti) I was running ten minute subs. Metaguide graph looked good. This was the first attempt at running longer than 5 minute subs. Initial test subs looked good in Liveview.
Back home, after bringing into Photoshop and enlarging slightly I could see short star tails that were not apparent on the camera screen nor until enlarged (these are not coma but short straight tails).

Is there any way to clean this up? Is it a mount limitation? a Metaguide setting issue? Any advice appreciated.
Reply With Quote
  #2  
Old 30-09-2014, 01:19 PM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,093
Are the star trails all in the same direction? This could quite possibly be differential flexure between the guidescope and imaging scope.

Do you notice a point on the guide graph where things start to go bad or worse than a previous point?

This is likely not a mount limitation.

Since you are using a Newtonian, the camera hangs off the side, so do you notice these subs go bad, only when pointing at a particular declination in the sky? (thinking of focuser flex and mount balance).

A 60mm guide scope (is that the focal length) wont be able to guide near the resolution of the imaging scope.

HTH, Josh
Reply With Quote
  #3  
Old 30-09-2014, 01:35 PM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,311
Yes the star trails all point in the same direction. The 60mm guidescope refers to the apeture, the guidescope focal length is 280mm.

There is no discernable flex. There are no tails at shorter sub lengths.
Reply With Quote
  #4  
Old 30-09-2014, 01:43 PM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,093
Glen,

What does a short sub exposure show?
Can you post a picture of the trails in question?

josh
Reply With Quote
  #5  
Old 30-09-2014, 02:37 PM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,311
Subs of 5 minutes or less show nice tight round stars with no tails. I am thinking I need to do more testing to see exactly where they start to occur and in what part of the sky.

No I won't be posting any photos as I have no way of resizing to suit this forum and the resizing apps I have tried makes the quality terrible.
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 05:41 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
OzScopes Authorised Dealer
Advertisement
Lunatico Astronomical
Advertisement
Bintel
Advertisement
NexDome Observatories
Advertisement
SkyWatcher Australia
Advertisement
Meade Australia
Advertisement
Celestron Australia
Advertisement
Astronomy and Electronics Centre
Advertisement