#1  
Old 18-01-2012, 02:44 AM
vic4loc (Victor)
Registered User

vic4loc is offline
 
Join Date: Jul 2011
Location: Sydney
Posts: 132
Help with taking Flats

I'm trying to capture flats, not sure if I'm doing it correctly.

I have a LX90 8" and QSI583, I simply point the scope about 20 Dec west at sunset, put the scope out of focus, took a few shots to get the average ADU value around 25000-30000, and got the image below.

What is that blob in the middle? Is this the expected flat image from an SCT? Do I need to put the scope into focus?

I have tried putting a white cloth over the scope, still getting that blob in the middle.

Any advise would be greatly appreciated.

Victor.
Attached Thumbnails
Click for full-size image (L-flats.jpg)
178.4 KB23 views
Reply With Quote
  #2  
Old 18-01-2012, 05:09 AM
mill's Avatar
mill (Martin)
sword collector

mill is offline
 
Join Date: Oct 2006
Location: Mount Evelyn
Posts: 2,922
First of all, never put the scope out of focus.
You have to leave everything the same as your imaging session or your flats will be useless.
Reply With Quote
  #3  
Old 18-01-2012, 06:29 AM
leon's Avatar
leon
Registered User

leon is offline
 
Join Date: Apr 2006
Location: Warrnambool
Posts: 12,421
Wow that is a big blob, is that a cropped image, or as taken, seems very unusual, but as Martin says, keep it focused.

Leon
Reply With Quote
  #4  
Old 18-01-2012, 10:07 AM
vic4loc (Victor)
Registered User

vic4loc is offline
 
Join Date: Jul 2011
Location: Sydney
Posts: 132
The image is uncrop.. I will try taking flats again with the scope focus. Thanks for the feedbacks.

Victor.
Reply With Quote
  #5  
Old 18-01-2012, 10:50 AM
Rigel003's Avatar
Rigel003 (Graeme)
Registered User

Rigel003 is offline
 
Join Date: May 2006
Location: Adelaide, South Australia
Posts: 1,079
If your scope was well out of focus the central blob is likely a shadow of the secondary. It's important for flats to be taken with exactly the same optical setup as your light exposures, including focus and rotation angle of camera, reducers, filters etc. If you're taking twilight flats the white T shirt over the end of the scope is a good idea to even out the background and stop individual stars from registering. Best solution of all is to buy a light box from Peter. Highly recommended.
http://www.iceinspace.com.au/forum/s...ad.php?t=49736
Reply With Quote
  #6  
Old 18-01-2012, 12:18 PM
DavidTrap's Avatar
DavidTrap (David)
Really just a beginner

DavidTrap is offline
 
Join Date: Jun 2009
Location: Brisbane
Posts: 3,032
Definitely the secondary shadow.

I went down the light box route to get 3+ second exposures to avoid any shutter blur with shorter exposures on my QSI.

DT
Reply With Quote
  #7  
Old 18-01-2012, 12:24 PM
swannies1983 (Dan)
Registered User

swannies1983 is offline
 
Join Date: May 2006
Location: Adelaide
Posts: 781
I use Al's Virtual Light Box (resources section). I'm happy with the results so far.
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 05:05 PM.

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