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Are darks worth the effort?


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Until last week, I only had one battery for my camera and on a cold night it only lasts for about 2 to 3 hours of constant use, so I prefer to spend all of that time taking images of the sky rather than splitting it between the sky and the back of the lens cap.  My darks are therefore usually done the next day when the battery has been recharged or existing darks are used.

Having recently downloaded EXIFLOG, I examined the temperature of some lights and their ‘associated’ darks (i.e. those that I had used for the images) only to find that there were some discrepancies – the darks recorded a higher temperature than the lights.  So I decided to generate a new set of darks, and as it is so mild at the moment, I put the camera in the fridge whilst I took them.

Having checked the temperature of the new images, to my surprise they were even higher than the ones I had previously used.  So I thought I would see what effect the new darks had on the final image (on the assumption higher temperature means more noise).  In short, none.  The resulting image using the new darks was identical to the resulting image using the original darks.  I then stacked the images using no darks at all and again the resulting image was identical. (Even the measured background noise on the R, G and B channels showed no difference.)  The only difference I could see when not using darks was the appearance of hot pixel trails when using average stacking but these disappear when using Kappa Sigma stacking (which I always do anyway to get rid of plane and satellite trails).

So has anyone else noticed this?  And can I now abandon creating darks?

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Oops, that should read NO darks for both images. 

I dither, using APT and PHD 2. I adds a few seconds in between subs but gets rid of hot and cold pixels. I have not used Darks for over a year now but I do take Flats and sometimes Bias's as well.

Check this out; https://astrofriend.eu/astronomy/tutorials/tutorial-dithering/tutorial-dithering.html

 

Cheers

Ron

 

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I am assuming DSLR.

Darks I found with mine are needed but reusing has been fine within a few degrees, winter and summer though need seperate ones I found.

Having said that it was an older cam and things might have changed.

 

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9 minutes ago, Ron Clarke said:

I dither, using APT and PHD 2. I adds a few seconds in between subs but gets rid of hot and cold pixels. I have not used Darks for over a year now but I do take Flats and sometimes Bias's as well.

Check this out; https://astrofriend.eu/astronomy/tutorials/tutorial-dithering/tutorial-dithering.html

 

Cheers

Ron

 

Useful, thanks Ron. Since my polar alignment is never very good, the hot pixels already move from frame to frame with respect to the stars so with Kappa Sigma stacking I shouldn't need to dither 😊

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44 minutes ago, Ron Clarke said:

Why is your PA never very good, what method do you use??

I just use my polar scope (drift alignment just takes up more valuable imaging time).  According to my SkyWatcher hand controller I usually get within 15' and according to PHD2 it's usually less than 5'.  Both are acceptable to me since, as I can only image for 3 min before the sky pollution gets too excessive, I don't see any field rotation in the images.  Here's a couple of my test images enlarged.

 

20 images average stacked with darks (hot pixel and a planes right hand wing light, no doubt on it's way into EMA)

 

large_av.jpg.0bcac26908a97f491542709371abd988.jpg

 

The same 20 images Kappa Sigma stacked with no darks

 

large_ks.jpg.c5c6e392c8758c33aa165baebff4b111.jpg

 

 

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7 minutes ago, Clive said:

I just use my polar scope (drift alignment just takes up more valuable imaging time).  According to my SkyWatcher hand controller I usually get within 15' and according to PHD2 it's usually less than 5'.  Both are acceptable to me since, as I can only image for 3 min before the sky pollution gets too excessive, I don't see any field rotation in the images.  Here's a couple of my test images enlarged.

 

20 images average stacked with darks (hot pixel and a planes right hand wing light, no doubt on it's way into EMA)

 

large_av.jpg.0bcac26908a97f491542709371abd988.jpg

 

The same 20 images Kappa Sigma stacked with no darks

 

large_ks.jpg.c5c6e392c8758c33aa165baebff4b111.jpg

 

 

Oops, that should read NO darks for both images. 

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