#1  
Old 15-03-2019, 03:08 PM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 1,495
Removing focal reducer yields *more ADU?

Hey there,

I was just going through some test data I shot with my RC10.

To get the native focal length of the scope I took a frame without the focal reducer in place (Telecompressor CCDT67).

When I looked at the statistics, the shorter focal length image (the one with the field flattener) captured less ADU than the one with; 787 ADU Vs 923. All variables were otherwise the same.

Seems counterintuitive that a slower system should be, erm, faster?

Weird.

I'll test it again when I get the opportunity to verify - this was based on two individual 1 sec exposures.

It could be anomalous short exposure response of the 1600.

Markus
Reply With Quote
  #2  
Old 15-03-2019, 03:45 PM
Slawomir's Avatar
Slawomir (Suavi)
Registered User

Slawomir is offline
 
Join Date: Sep 2014
Location: North Queensland
Posts: 3,240
Quote:
Originally Posted by Stonius View Post
Hey there,

I was just going through some test data I shot with my RC10.

To get the native focal length of the scope I took a frame without the focal reducer in place (Telecompressor CCDT67).

When I looked at the statistics, the shorter focal length image (the one with the field flattener) captured less ADU than the one with; 787 ADU Vs 923. All variables were otherwise the same.

Seems counterintuitive that a slower system should be, erm, faster?

Weird.

I'll test it again when I get the opportunity to verify - this was based on two individual 1 sec exposures.

It could be anomalous short exposure response of the 1600.

Markus
Could it be that the bias / moon phase / target was different in these two scenarios?
Reply With Quote
  #3  
Old 15-03-2019, 05:03 PM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 1,495
Thanks Suavi,

the culprit was, well, my own stupidity.

I was sure all variables were the same, but when I examined the FITS headers, I realised that somehow I'd managed to take one exposure at 1 second and the other at 10 seconds, hence the difference.
Duh.
I can only assume that I either adjusted the exposure or entered it wrong. Not impossible as I was more interested in getting fields to solve for focal length calculations than comparative ADU.

Ahem, as you were.

Markus
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 06:52 PM.

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