Jump to content
  • Join the online East Midlands astronomy club today!

    With active forums, two dark sites and a knowledgeable membership, East Midlands Stargazers has something for everyone.

Darks?


Celeste
 Share

Recommended Posts

I finally managed to get the scope out for a bit the other night, I tried imaging M42 again, but this time using it in 2" size (so I could get a little bit more image on the small CCD) I also took darks this time too....now my question is, do darks make the image better? Or at least, are they supposed to? My image is pants to say the least with darks added. I can get more data out without the darks, than with. I don't seem to have captured much data at all this time, I took 60secs subs like last time, but I did add the coma corrector (I coudn't get focus without it) Would that cause me issues? I took my darks at the same time as my subs, nothing was changed or moved....only adding the cap to the end of the scope, as the manual tells me to. Is there a 'knack' on adding darks? I use Astro art 3 or DSS.


Link to comment
Share on other sites

Guest bunnygod1

Dark frames are made at the same exposure time and ISO as the subject light frames, but with no light reaching the sensor. Their purpose is to remove the thermal noise/hot pixels from the light frames. Normally you want between 10 and 20 dark frames during each imaging session.
 

Link to comment
Share on other sites

The manual suggests 1 dark frame per sub....same settings etc. I did just that, 20 60sec subs and 20 60sec darks, add the darks and my image has low data, minus the darks it's a little better. Although the subs I have now aren't very good, I'm wondering if it's because I used a coma corrector? GAH this imaging malarky is a right PITA


Link to comment
Share on other sites

I was told by a very clever guy who designs TV cameras this.


The max number of dark's you need is 21.


Because of the multiplication factors involved to get the same signal to noise ratio of 21 Dark's the next number will be something like 85 Dark's.


He also told me that if you have too many Dark's the stacking program will convert consistent hot pixels into stars.


It is better to use an odd number of Dark's and a ratio of 1 dark per 5 lights up to 21.


Do not ask me to explain any of technical details of this as it is way above my head.


I have taken his advice on board and stuck to it ever since and it does work.


Edited by Graham
Link to comment
Share on other sites

I've come to the conclusion this set of subs are pretty naff, to be polite (to myself lol) My last lot of 60sec subs, on 1.25" size and IR filter....were MUCH better than 2" size, coma corrector and no filters (I dont have any 2" filters) I can't get much from this 60sec lot :(


 


I'm saving for an Atik 314l+, ST80 and hopefully an ED80 soon anyway :) (well, soon as in after summer hols!)


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.