Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 02-12-2013, 09:01 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Problem with flats, Orion Starshoot and MaximDL5

My instruction manual tells me to take flats at 0.1 second and look for a FWHM of around 20000.

At 0.1 I'm getting FWHM values of 35000 to 40000
At 0.5 I'm getting FWHM values of 50000 and up
at 0.01 I'm getting FWHM values of 28000.

0.01 is a small fraction of 0.1 so is this right? will it work? I've tried reducing the exposure times even further but that's getting into the realm of bias frames is it not?

Oh, and I;m using a light box.

Correction: everyhwere I have said FWHM, I meant MAX pixel value.... oops.
Attached Thumbnails
Click for full-size image (IMG_6646.jpg)
176.3 KB34 views

Last edited by bloodhound31; 02-12-2013 at 09:31 PM.
Reply With Quote
  #2  
Old 02-12-2013, 09:22 PM
troypiggo's Avatar
troypiggo (Troy)
Bust Duster

troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,827
Instruction manual for a camera can't tell you what exposure to take flats with a light box, as it depends on how bright the light box is. What you're after is a histogram that isn't clipped at either end, and a peak in the histogram around 1/3 to 1/2 way along from the dark end. Depends who you talk to. I don't think the correct term is FWHM either, that's usually referring to stars. Maybe ADU count? Any way, if you use the histogram it's irrelevant as the peak will do the job for you.

My flat exposures are very short, especially for Lum filters. 3nm SII is much longer obviously. Don't worry about how short the exposure is, as long as it's not too fast for your shutter - ie you don't get half the image dark. If you're still getting even illumination, that's all that's important.
Reply With Quote
  #3  
Old 02-12-2013, 09:32 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Thanks Troy.
Reply With Quote
  #4  
Old 03-12-2013, 11:40 PM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,392
I like to aim for around 28k to 30k for flats. That usually gives a good illumination
Reply With Quote
  #5  
Old 04-12-2013, 02:25 PM
troypiggo's Avatar
troypiggo (Troy)
Bust Duster

troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,827
But those values would be camera-specific (or more correctly, sensor-specific) wouldn't they? They're a function of the well depth?
Reply With Quote
  #6  
Old 05-12-2013, 11:48 AM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
Quote:
Originally Posted by troypiggo View Post
But those values would be camera-specific (or more correctly, sensor-specific) wouldn't they? They're a function of the well depth?
They would be sensor specific if the units were electrons, but we're talking ADU. The gain is usually set so that full well gives an ADU count around 2^16. Around 30,000 ADU means half of full well, whatever that happens to be for the specific sensor.
Reply With Quote
  #7  
Old 05-12-2013, 01:07 PM
troypiggo's Avatar
troypiggo (Troy)
Bust Duster

troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,827
Gotcha. Thanks mate.
Reply With Quote
  #8  
Old 07-12-2013, 12:26 AM
2stroke's Avatar
2stroke (Jay)
The devil's advocate

2stroke is offline
 
Join Date: Jul 2011
Posts: 816
Dim your light box bud, its to bright i just call it the count or value lol no need to say analog digital unit we all know that already haha, and paul is right on the dollar.
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 08:28 AM.

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