M51 with first time dithering just to see..

[steviemac500]

So i tried it out last night and used APT for the first time to control the session. 15 8minute subs dithered@ ISO 800. No darks, 20 flats and 40 bias. I stcked them using the Kappa method which i believe was right and frankly I'm amazed that there is a little noise. I ran itthrough HLGV too. There is still a lotof noise but for a first go, and compared to yesterday's, its not bad!!!

[Dave In Vermont]

Very nice image! Thank you for posting it!

Please do continue,

Dave

[Knighty2112]

Nice image. Well done!  I saw M51 for the first time last night. Considering the LP from my back garden I could see the two cores of each Galaxy very easily. Hoping at least on every observing session to see a new fuzzy every time if possible! 

[Peco4321]

36 minutes ago, Knighty2112 said:

Nice image. Well done!  I saw M51 for the first time last night. Considering the LP from my back garden I could see the two cores of each Galaxy very easily. Hoping at least on every observing session to see a new fuzzy every time if possible! 

What scope do you need to see that detail?  I have 150p eq3-2 and couldn't find it, although after spending a bit of time studying some pictures I took just 25 sec exposures (not through scope) and looking at stellarium, next time I know better where to look!  

[Paul73]

8 minutes ago, Peco4321 said:

What scope do you need to see that detail?  I have 150p eq3-2 and couldn't find it, although after spending a bit of time studying some pictures I took just 25 sec exposures (not through scope) and looking at stellarium, next time I know better where to look!  

In short. You are unlikely to see that clarity under UK sky. There is a faint suggestion of spirals in my 10" and a bit more of a suggestion in 16".....

I've never seen it through a big scope under truely dark stable sky.

Paul

[Knighty2112]

21 minutes ago, Peco4321 said:

What scope do you need to see that detail?  I have 150p eq3-2 and couldn't find it, although after spending a bit of time studying some pictures I took just 25 sec exposures (not through scope) and looking at stellarium, next time I know better where to look!  

I saw it with my Skywatcher Startravel 120 frac, so should think you should see it also pretty good with your 150p. Could see the two bright cores, and the nebulosity of the spiral arms between the two cores. Larger scopes I'm sure will bring out much more detail, but it was pretty easy to see. Best views were with my 17 & 15mm (x35 & x40 views) EP's for best sky contrast.  

[wigggyy]

Lovely image one of my personal favourites thanks for sharing

[steviemac500]

Thank you for the positive comments everyone. Can anyone comment on the need for darks when dithering?

[Marky1973]

Nope...at least not yet! 

There does seem to be the suggestion that they are not needed - I had a go at M51 last week and stacked/processed in PIXINSIGHT - when I get half a chance (hopefully starting tonight) I will have a go at processing without the darks and see how I get on - copying the process as closely as possible. I did dither via APT so will be interesting to see if there is a big difference.

Great image by the way - I really like this target as well - it is just so small in my ED80!

[Physopto]

Very nice image. Well done.

Derek

[steviemac500]

2 hours ago, Marky1973 said:

Nope...at least not yet! 

There does seem to be the suggestion that they are not needed - I had a go at M51 last week and stacked/processed in PIXINSIGHT - when I get half a chance (hopefully starting tonight) I will have a go at processing without the darks and see how I get on - copying the process as closely as possible. I did dither via APT so will be interesting to see if there is a big difference.

Great image by the way - I really like this target as well - it is just so small in my ED80!

Cool. This was through my ED80 but cropped a fair bit without darks. It will be interesting to see how yours compares? Let me know whhen you're done processing?

[wimvb]

Very nice image with detail in the galaxy and the noise in the background under control.

Darks are not crucial when using a DSLR/CMOS, if you dither. They can help removing hot pixels and controlling amp glow. But they can sometimes also do more harm than good. I'd suggest stacking with and without darks and have a look at the difference, as Mark suggested.

Hot pixels can also be removed by cleaning the raw files in a suitable software (I've used RawTherapee for this on occasion) or during the calibration/stacking process. Both DSS and PI have settings for this.

[ollypenrice]

How big was your dither? For DSLRs I gather something like 12 pixels is best. (Suggestion of Tony Hallas.) I ask because there is clearly some systematic patterning on quite a large scale in the background sky. We see both large scale horizontal and diagonal banding. I wonder if a larger dither would destroy that?

Olly

[Marky1973]

2 hours ago, steviemac500 said:

Cool. This was through my ED80 but cropped a fair bit without darks. It will be interesting to see how yours compares? Let me know whhen you're done processing?

Will do - PI is currently doing its thing somewhere around image 13 of 22! :-)

[Marky1973]

Mmmm....image without darks has come up much noisier than the image with darks, despite dithering - however, I am not 100% sure I followed the processing workflow in exactly the same way for both images, so I will have to try again with a stricter regime - so the jury is still out in my case.... :-)

[steviemac500]

I've done a couple with darks and an increased pixel size on the advice on Olly, and I have to say that the darks made the images much cleaner.

[ollypenrice]

You should also remember that you have just 2 hours' worth of data. If you're cruising the net looking at good M51 images you'll find that 20 hours is perfectly normal.

Olly

[steviemac500]

Can you clarify Olly? Is dithering more effective with much longer data?