#1  
Old 06-08-2013, 11:26 PM
graham.hobart's Avatar
graham.hobart (Graham stevens)
DeepSkySlacker

graham.hobart is offline
 
Join Date: Nov 2008
Location: hobart, tasmania
Posts: 1,973
hot pixel advice

Hello, tonight I am imaging with a cooled 60da FS 60 whilst at the same time taking some shots through the RC 8/QSI combo. Both are being guided via PHD on a mini guide scope. So because I have them both going I can't dither in Maxim which is the only thing I can get to dither for some reason. So now have some nice shots with hot pixels. I have Star Tools and PS 5, I also have PI but I have yet to tackle that. Obviously I have Maxim.
The frames are Canon Raws.
What can I do to get rid of the hot pixels besides dithering, I have heard of hot pixel maps but have never used one.
Cheers
Graz
Reply With Quote
  #2  
Old 07-08-2013, 01:00 AM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,093
Im sure PI (probably maxim too) would have an algorithm for rejecting hot pixels during stacking. I know ccdstack2 does, dont know about star tools. sorry i cant provide more help.

Josh
Reply With Quote
  #3  
Old 07-08-2013, 05:54 AM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 15,409
Use darks, bias and adaptive dark subtraction. CCDstack may do it. Images Plus does it. Maxim probably does as well.

Take a shot of the same exposure details (length, ISO etc) with the lens cap on at night so no light leaks. Ideally take 16 but less would work.
Sigma reject combine these darks to make a master. Subtract a bias master from them during the procedure.

A bias master is same settings except the shortest exposure time. Its a picture of the noise from the electronic readout of the camera.

Take several, sigma reject combine.

Ideally you do the above at the same temperature you image at. Noise varies with temperature. Adaptive darks help overcome that but try to minimise the diffference.

Once you've made your dark master try to standardise your exposure and ISO settings so they are not all different to make the dark work best.

Work out what that is for your camera. A 60Da is probably around ISO1200 max and depending on your light pollution/ tracking accuracy of your mount maybe 5 or 10 minutes. Bad light pollution needs shorter exposure lengths and a light pollution filter.

Also, why can't you dither with them both going? There's only one guide scope and camera. Can't you dither that and it dithers both?

I hope this helps.

Greg.
Reply With Quote
  #4  
Old 07-08-2013, 08:41 AM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
In PixInsight you can use the CosmeticCorrection process to deal with hot and cold pixels.
Reply With Quote
  #5  
Old 08-08-2013, 07:52 PM
graham.hobart's Avatar
graham.hobart (Graham stevens)
DeepSkySlacker

graham.hobart is offline
 
Join Date: Nov 2008
Location: hobart, tasmania
Posts: 1,973
hot pixels

Greg, was using different duration of lights for each camera so was worried when one was dithering the other was still exposing etc. Did lots of darks but no bias frames, will di this and flats this weekend. I am sure deep sky stacker automatically subtracts but will check. Cheers
Graham
Reply With Quote
  #6  
Old 11-08-2013, 07:37 AM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 15,409
Quote:
Originally Posted by graham.hobart View Post
Greg, was using different duration of lights for each camera so was worried when one was dithering the other was still exposing etc. Did lots of darks but no bias frames, will di this and flats this weekend. I am sure deep sky stacker automatically subtracts but will check. Cheers
Graham

I see. There are a lot of advantages to standardising the length of your subs otherwise you get this huge library of darks etc that becomes hard to maintain.

I usually only use a few different exposure lengths.

Tracking performance of your mount really determines how long you can go. Longer is usually better than shorter except in DSLRs. Narrowband needs longer to get past the noise.

Greg.
Reply With Quote
  #7  
Old 12-08-2013, 08:20 PM
Geoff45's Avatar
Geoff45 (Geoff)
PI rules

Geoff45 is offline
 
Join Date: Jul 2006
Location: Sydney
Posts: 2,407
Quote:
Originally Posted by RickS View Post
In PixInsight you can use the CosmeticCorrection process to deal with hot and cold pixels.
Works well. I use it all the time. CCDStack also has an easy-to-use method of making a hot pixel map that works well.
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 08:02 PM.

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