Darks

[ultramol]

Can I use darks taken the day after on another imaging session. The focus and times were the same, temperature I would say close to the same, if not the same the only difference was the target. Its a bit confusing this !! On monday my lights were fine but my darks failed. On tuesday my lights were fine and my darks were fine, Everything the same so will the darks from tuesday be ok for the lights of monday, whew.....that took some sorting out....lol

[Leveye]

I have and they worked perfect. Matching the ISO and time is crucial though. The temperature you have some leeway with from what I discovered..

[Purplehayze104]

from wot ive heard many people who image make a darks library of various lengths, iso's & temps so as they don't have to do them at the end of an imaging session just load up the closest to wot you have been shooting at then load em in.

[ultramol]

Cool, I will now have a go at some image processing...many thanks.....geoff

[Davesellars]

For a DSLR I wouldn't bother taking darks after a session. You cannot assure the same sensor temperature and if you're shooting longish exposure it's highly unlikely you'll get enough of them.

Check the sensor temperature coming from EXIF data of the camera for both lights and darks and match them when stacking.  If you took the darks outside for example at the end of the session but took a break for 5 mins before taking the darks after completing the lights the sensor temperature could quite easily have dropped a significant amount essentially rendering the darks worthless.  It has nothing to do with the ambient temperature outside, whatever that is the sensor temperature will go up / and down quickly to start and depending on the camera and ISO it can take quite a while to stabilise.

From my analysis (rather unscientific though), there are sudden leaps in noise as the sensor temperature rises.  For example I see quite a difference in the level of noise from the sensor temperature at 19C to 20C, then it seems to flatten out a bit and then a large leap again up at 26/27C. There are reasonably significant differences for me in 1 degree C it would make sense to match to the nearest degree C the temperature of the light to the dark when stacking.  It may seem a bit of faff but it's simple in deep sky tracker using a group for each temperature of light and dark and put common files in the first group.

[udaiveer]

from wot ive heard many people who image make a darks library of various lengths, iso's & temps so as they don't have to do them at the end of an imaging session just load up the closest to wot you have been shooting at then load em in.

I have a library. Of diff ISO n times.

I use a timer.

I realised u can get higher temperatures (closer to Lights ) after a few darks in the camera bag!!

I think I will have to periodically update to keep up with "dying" pixels.

Sent from my iPhone using Tapatalk

[ambro]

Some programs  has dark frame scaling feature:

http://www.cyanogen.com/help/maximdl/Dark_Frame_Calibration.htm

[ultramol]

Some programs  has dark frame scaling feature:

http://www.cyanogen.com/help/maximdl/Dark_Frame_Calibration.htm

Does DSS have this feature ?

[ambro]

DSS dosen't have dark scaling feature.

Another software withn dark scaling  is PixInsight

http://www.pixinsight.com/tutorials/master-frames/index.html#Dark_Frame_Scaling_Considerations.com/tutorials/master-frames/index.html#Dark_Frame_Scaling_Considerations

[davew]

It is my understanding that DSS has dark " Optimisation ". 

I'll quote the author of DSS here. This was in an answer to a question on the topic.

 you can use the dark optimization option that will try to reduce the differences by analyzing the light and dark hot pixels (but without using the exposure times info).

One problem with trying to optimise darks the normal CCD way is that some DSLRs don't give true Raw files. Canon's when tested ( According to Craig Stark ) don't give a true Raw because they reduce the dark current. Dark current should increase over time and temperature but he found it actually reduced. I'm assuming everyone is referring to Canon and not any other make !

I'd try the Dark Optimisation for yourself and see what happens.

Dave.

[ultramol]

I will try that and re run my data, thanks again