Am I taking FLATS correctly in Artemis - pic attached

[Fordos Moon]

I read up on this and noted the 20k ADU target for each filter but was somewhat surprised by the long exposure time required for the Ha filter. Can anybody please check the screenshot below and confirm I am on the right track?!

Many thanks, Bob

I was also shocked at how dirty the lens on my ED80 was (didnt notice when using DSLR up to now) - tips for cleaning? (Presume not as precious as cleaning the mirror in my dob!)

Final question - when I take the BIAS frames, I read only need one set for all filters. Is this right and presume if that the case the binning selected doesnt matter?!

[PhotoGav]

My research led me to an average value of around 32000 ADU for flats. I don't know how much you have screen stretched the image above, so can't judge the flat really. Normally there is an obvious vignetting to the image though and it is a roughly mid grey tone with histogram peak around the 32k mark. Yes, the Ha exposure time will be significantly longer than the rest!

I noticed that my 80ED was a filthy beast too and took to the end lens with a lens cleaning cloth and some lens cleaning fluid, the stuff that I use for my Canon lenses. It is now a clean thing of beauty and I don't appear to have caused any damage or problems!

[Fordos Moon]

My research led me to an average value of around 32000 ADU for flats. I don't know how much you have screen stretched the image above, so can't judge the flat really. Normally there is an obvious vignetting to the image though and it is a roughly mid grey tone with histogram peak around the 32k mark. Yes, the Ha exposure time will be significantly longer than the rest!

I noticed that my 80ED was a filthy beast too and took to the end lens with a lens cleaning cloth and some lens cleaning fluid, the stuff that I use for my Canon lenses. It is now a clean thing of beauty and I don't appear to have caused any damage or problems!

Thanks Gav will do same with mine and prepare for new flats. The pic attached is a bit bright, i played around with the display settings and can concur my flats were off a light grey with a few blobs on them towards the outer edge - i guess processing tonight will tell!

[ollypenrice]

Bob, dirt on the objective will have no effect whatever on your flats. It is far too far from the chip to come to focus. (Think of secondary mirrors and reflectors. That huge black obstruction is not visible... ) I think your new bunnies will be coming from filters, chip window or reducer but not forward of there.

Bias are shot with no light allowed onto it so fiters play no role. A bias is a bias is a bias, so to speak. However, I would strongly advise you to take darks and biases with the camera off the rig and the metal screw-on chip window cover in place. That's one reason why Atik supply it. The tiniest light leakage will mar darks and bias and just putting a lens sheild on a scope is not enough, very often.

Although I can only speak for the dozen or so rigs I've used, every 'good' flat I've had followed the same pattern: a bright centre, fairly symmetrically located and darker corners, when given the right stretch to show this. Fuzzy bunnies or doughnuts scattered about to taste! But if the flat didn't show a general soft vignetting with dark corners it was never any good.

Not credible...

Credible...

Olly

Edit, I guess you are taking bias to use as darks for your flats? With a set point cooled camera I can't think of any other use for them.

[lensman57]

Your flats taken with NB filters will need a much longer duration since the HA filter for example will only pass very little of the full spectrum through. I aim for about 25000 ADU give or take 3000 units and usually these seem to work. Here is a typical flat of mine using a full frame DSLR @ F2.8 lens and a CCD with a small chip it has had one mighty stretch to bring out the anomalies . The flat clearly indicates none uniform illumination and a tilt of the optical axis plus distortion.

A.G

[Fordos Moon]

Bob, dirt on the objective will have no effect whatever on your flats. It is far too far from the chip to come to focus. (Think of secondary mirrors and reflectors. That huge black obstruction is not visible... ) I think your new bunnies will be coming from filters, chip window or reducer but not forward of there.

Bias are shot with no light allowed onto it so fiters play no role. A bias is a bias is a bias, so to speak. However, I would strongly advise you to take darks and biases with the camera off the rig and the metal screw-on chip window cover in place. That's one reason why Atik supply it. The tiniest light leakage will mar darks and bias and just putting a lens sheild on a scope is not enough, very often.

Although I can only speak for the dozen or so rigs I've used, every 'good' flat I've had followed the same pattern: a bright centre, fairly symmetrically located and darker corners, when given the right stretch to show this. Fuzzy bunnies or doughnuts scattered about to taste! But if the flat didn't show a general soft vignetting with dark corners it was never any good.

Not credible...

Credible...

Olly

Edit, I guess you are taking bias to use as darks for your flats? With a set point cooled camera I can't think of any other use for them.

Olly, delighted to have your comment as always! My flats do look like your lower image, only a lot brighter but maybe that is just my onscreen display (hopefully) and has the darker edge and one or two dust bunnies.

I took the bias i think just because I read somewhere I had to, alas I only added the scope cover - i should look into that screw on plate you mention, or is that the plastic dome thingy that it came with in the box?!! I did wonder what that was.

Now to find a step by step process to put my captures together. Ive got Nik Szymanek's "Shooting Stars" on my desk here at work so hopefully that will help me. I intend to use Deep Sky Stacker as that is what I have but I did take a note of some software you mentioned in a post somewhere else that I may purchase at a later date!

[Fordos Moon]

Your flats taken with NB filters will need a much longer duration since the HA filter for example will only pass very little of the full spectrum through. I aim for about 25000 ADU give or take 3000 units and usually these seem to work. Here is a typical flat of mine using a full frame DSLR @ F2.8 lens and a CCD with a small chip it has had one mighty stretch to bring out the anomalies . The flat clearly indicates none uniform illumination and a tilt of the optical axis plus distortion.

A.G

Thanks A.G. thats kinda what mine look like, only brighter on my screen. Will the stacking software (in this case DSS) process these as they are? I went for 20K ADU. Also I notice the Atik takes FITS files whereas my DSLR used CR2 files. Do you happen to know if DSS works with FITS files or do I need to convert them?

[PhotoGav]

I missed your question about bias frames...

I have a set for each bin level used (so far that's just 1x1 and 2x2). I shot 201 frames with the chip plate screwed in for each set at the chosen cooling point for all my frames (i.e. lights, darks & flats, I use -20ºC). The set is then stacked and used with the flats when creating each master flat.

Don't know about DSS I'm afraid.

[lensman57]

Thanks A.G. thats kinda what mine look like, only brighter on my screen. Will the stacking software (in this case DSS) process these as they are? I went for 20K ADU. Also I notice the Atik takes FITS files whereas my DSLR used CR2 files. Do you happen to know if DSS works with FITS files or do I need to convert them?

Yes DSS works with fits just the same. If the CCD is an OSC one then you need to choose the correct Bayer pattern from Options, Raw/Fits/DDP settings and under the  fits tab uncheck the Monochrome fits..... for a Mono CCD. As Olly said take your Bias and Darks off the scope with camera front well covered up. A lot of scopes do leak light.

A.G

[Fordos Moon]

Yes DSS works with fits just the same. If the CCD is an OSC one then you need to choose the correct Bayer pattern from Options, Raw/Fits/DDP settings and under the  fits tab uncheck the Monochrome fits..... for a Mono CCD. As Olly said take your Bias and Darks off the scope with camera front well covered up. A lot of scopes do leak light.

A.G

Its a mono, I used Ha, RGB filters. I didnt actually take any "darks" just "bias" (lens cap on - shortest exposure) so a little concerned now?

[lensman57]

Its a mono, I used Ha, RGB filters. I didnt actually take any "darks" just "bias" (lens cap on - shortest exposure) so a little concerned now?

You can always redo the bias off the scope, with set point cooling it should be a simple affair. You treat the R,G and B as Mono fits with their own flats and you should be good to go.

Regards,

A.G

[PhotoGav]

Darks can be an optional extra with a cooled CCD depending on the amount of noise / hot pixels generated. If you decide that you do want to use them, it's easy, you can create a library of darks shot anytime with the camera cooled to your chosen set point. You will need to do darks for each bin combination you use. I use 49 darks for each time and bin combination all at my chosen set cool point of -20ºC. You can then reuse the appropriate dark master from your library for each set of subs shot at that time and bin.