M101

[turbo 2011]

This was taken over 3 nights great British weather about 3.5 hours subs 2 min to 10 min darks added . This took a lot of work to bring out any great detail . Was chatting last night about sub lengths should they all be the same length or different one lad was saying just stick with 10 min subs for dslr I know noise is a problem with the longer subs but will the darks not cancel the noise out . Any thoughts on this one.

cheers lee

[michael.h.f.wilkinson]

Nice shot. Some satellite galaxies also showing up nicely

[peter shah]

A nice shot 101 is more difficult than you might think. Signal to noise is down to individual cameras but as a rule you do get better signal to noise with a longer sub length. There are a number of things that can increase the signal or decrease noise, faster optics, sky conditions, colder temperatures. I never take darks for any of my images, My camera doesn't have set point cooling and ive never been able to get a good noise match, my darks tended to take more out of my subs so I stopped doing them. Having said that I had an FLI camera that was very stable with set point cooling the difference removing the darks was so much better. Bigger pixels is another thing that is often overlooked. Most modern cameras are using smaller and smaller pixels which isn't good for astro imaging, the bigger the pixel the bigger the pixel area which means more photon hits, 50% QE with a pixel of 4microns isn't the same as 50% with 9 microns you have more than four times the surface area. Also the more pixels on a sensor can generate more noise. Bigger pixels will show less aberrations in your optics and will give you shaper views so matching the camera with your optics and your sky conditions is pretty important. Something else I should mention are good quality flats will allow you to push your processing further. I've rambled on enough I'm sure there are a few other points that I may have missed.

[sologuitarist61]

Nice one Lee

[stem1989]

Thats a great looking image, you should be very happy with this one. It looks a little over processed but not too much. One thing about M101 is dark skies will make a massive difference, I took 3 hours of data from my yard in Preston and wasn't very happy, but having taken only 60 minutes from a darker site the image was deeper in detail than the 3 hour version.

Its just one of those low surface brightness targets that requires a lot of time

Its a great image though.

[turbo 2011]

No darks like the sound of that I've always hated taking darks . flats is something I will have to give a go some time thanks for the info. Any advise on flats not to sure how todo this . Do you cover the tube with a white sheet have a bright light the other side of sheet and that's it any help on this one please .

[astro mick]

Yes.

I have an old Starlight Xpress camera,that doe,snt require darks.In fact Darks takes detail away from the image.

[peter shah]

just to make myself clear its better to remove dark current providing you can get a good match with the light frames, I've not been able to do it with my none regulated camera. As for flats , my general rule is after an imaging session I leave the focus in exactly the same place just in case I need a fresh set of flats. Its not always easy if you don't have your own observatory or you out on location somewhere. Most of the time I will do sky flats at twilight just before an imaging session without anything covering the scope at all, if I don't get the chance I will do them after either with a light box if its still dark or with a diffuser if its cloudy (at twilight). To get good flats you need to expose 30-50% saturation of your sensor if you don't there is a danger of introducing noise into your light frames. For my camera I will aim for an ADU of about 22000 and I do around half a dozen in each filter, its important to calibrate the flat frames before calibrating your lights to get an accurate correction. Hope this helps

[turbo 2011]

Yes it does thanks

[Gina]

Nice image - particularly with a DSLR