M101 First Attempt

[Gerry Casa Christiana]

Hello all

Just thought I would share my first go at M101. Hope it's ok!

http://www.astrobin.com/full/289155/0/

Kind regards

 

Gerry

 

 

 

[tooth_dr]

Hi Gerry

There is plenty of detail in there. It maybe looks a little blue but could be my screen?

 

Great image though, thanks for sharing.

 

Adam

[Gerry Casa Christiana]

Just now, tooth_dr said:

Hi Gerry

There is plenty of detail in there. It maybe looks a little blue but could be my screen?

 

Great image though, thanks for sharing.

 

Adam

No your right I only processed it in 15 minutes so very quickly. I also always do photos with the dslr in tungsten mode as I notice it works better for me but can make things slightly more blue. 

Cheers

 

[Adam J]

How much data was that? sub lengths number of subs etc. 

[Gerry Casa Christiana]

1 hour ago, Adam J said:

How much data was that? sub lengths number of subs etc. 

Hello Adam

Yes sure. I did 25 subs @ 120 seconds  at 3200 with 179 bias frames with 29 flats. I'm experimenting with using bias instead of darks. 

Cheers 

Gerry 

[Tommohawk]

8 hours ago, Gerry Casa Christiana said:

Hello Adam

Yes sure. I did 25 subs @ 120 seconds  at 3200 with 179 bias frames with 29 flats. I'm experimenting with using bias instead of darks. 

Cheers 

Gerry 

Hi and that's a nice image of M101, and nicely processed.

I usually find auto white balance works best with my Canon - not sure which camera you're using. Also you probably want to be using darks and bias, not one or other.

Oh - just saw the header on astrobin - Canon 550D same as me. Your stars look nice and round so your mount must be working well - maybe you could extend your subs. Did you try longer exposures?

[Gerry Casa Christiana]

Hello there!

Sorry I just saw your message now! Yes it's a 550d and yes I have done longer exposures but without autoguider I tend to lose more frames the higher I go. I could do 3 minutes but im not sure I'm getting much more for that? 

I have researched a little and so the wise ones say darks frames become nor important in hotter weather but bias are more important in winter. I do try both really and this is my first picture without darks to test the theory. 

Ill try longer exposures when the alignment is good! Some nights it's good and others not so good. 

What sort of settings are you using for your camera?

Gerry

[Tommohawk]

First thing to say is your image is already really pretty good - I did M101 last year with 8 minute subs (although only 14 of them as guiding was playing up) and Skywatcher 200 and TBH its not a whole lot different!

But if you're looking to improve consider the following.

Work with RAW files, not JPEGS - not sure if you've already twigged that. Try and extend your exposure time if you can, but as you say if your images end up with trails that's no good. ISO 800 seems to be favoured by Canon users generally - thats what I use - but of course for shorter subs you may need higher ISO. You image doesn't look noisy to me at all - not quite sure how you achieved that! Maybe I need to rethink my standard use of ISO800.

Obviously polar alignment is crucial if you aren't guiding. Generally the closer to the pole you are the less tracking error you should have, provided PA is good.

I would always use bias, darks, and flats - it may be that darks are more important when the camera is hot, but I cant see any advantage in not using them. Maybe if the darks arent matched for ambient temperature it might be a problem. In the UK this isnt normally an issue - it's always cold!

Have fun!

[Gerry Casa Christiana]

Hello

Thanks for everything. It's nice to talk to someone with the same camera. I will say this though ISO 800 is a lot more noisy than 1600 and 3200. Most people use 1600 for ours but I'm doing shorter subs as you say. Try this the next time you are out. Put your camera in tungsten mode instead of daylight it picks up better nebula detail with the sacrifice of it being slightly blue but you don't get the orange sky glow colour. I've done comparison shots of the Rosette (my best picture) of daylight and tungsten and you can see the obvious difference. Try it! 

The darks so the learned tell me already include the bias so if you use them together your actually injecting noise into the photo. That's what the experts say BUT I'm testing the theory but I would never use 800 on mine they are far noisier. 

This is how I know  

http://www.sensorgen.info/CanonEOS-550D.html

Give it a try at 1600  nice talking to you  

 

Gerry

 

[Tommohawk]

3 hours ago, Gerry Casa Christiana said:

Hello

Thanks for everything. It's nice to talk to someone with the same camera. I will say this though ISO 800 is a lot more noisy than 1600 and 3200. Most people use 1600 for ours but I'm doing shorter subs as you say. Try this the next time you are out. Put your camera in tungsten mode instead of daylight it picks up better nebula detail with the sacrifice of it being slightly blue but you don't get the orange sky glow colour. I've done comparison shots of the Rosette (my best picture) of daylight and tungsten and you can see the obvious difference. Try it! 

The darks so the learned tell me already include the bias so if you use them together your actually injecting noise into the photo. That's what the experts say BUT I'm testing the theory but I would never use 800 on mine they are far noisier. 

This is how I know  

http://www.sensorgen.info/CanonEOS-550D.html

Give it a try at 1600  nice talking to you  

 

Gerry

 

Hi Gerry

The sensorgen info is misleading if you just look at the lowest point of the graph. For a detailed explanation see:

here

and for the specific info on the Canon 550D see:

here

This definitely suggests ISO 800 is favoured.....

That said, it doesn't take into account 2 critical points.

1. If you cant do a long enough exposure because of guiding issues you may be better to raise the ISO

2. If the sensor overheats with longer exposures you may be better to raise the ISO.

For those reasons you may want to use higher ISO (and I have done so when using a UHC filter) but it remains the case that you should aim for longer exposures and avoid high ISOs. 

Regarding calibration frames - ie Darks Flats Bias - I'm not sure that combining darks and bias is incorrect, that seems curious. The makers of the stacking software Deepskystacker have this as a good source of information.

PS not sure if youve tried this yet, but the 550D also has video crop mode which is excellent for planets. Probably need a barlow or powermate for that though.

cheers

Tom

 

[Gerry Casa Christiana]

Hi there 

Yes I've already read those 2 articles before  thanks though. Yes I read those articles and then switched to 800 before for me I noticed more noise but I'm not guiding and I expect that makes a big difference. 

Yes the bias thing I've read on numerous sites (like I said I'm testing it!) Craig Stark says it as well as others. I can test it again though! I think it is a case of what works don't you think? When I'm autoguiding I know I cannot use those high ISO. It's a interesting subject because there are so many conflicting ideas  it's part of the fun finding out. 

Its like dithering. My pictures seemed worse! But I intend to go back to that too.

great fun!

[Tommohawk]

11 minutes ago, Gerry Casa Christiana said:

 It's a interesting subject because there are so many conflicting ideas
 

Well thats for sure! I was kinda hoping the learning curve would flatten out a bit.... but it just seems to get steeper!

[Gerry Casa Christiana]

Absolutely! But I just give away anything I learn but it's so individual as well because of all the different equipment.  Autoguiding next! So I'll be back to pick your brains. 

Gerry

[frugal]

Different software handles darks and bias in different ways. PixInsight for instance subtracts the bias from the dark, then it scales the dark for each light. So it subtracts the bias and the scaled dark rather than subtracting a fixed (dark + bias)

[Gerry Casa Christiana]

Ah that's good to know so you can use both in effect? I may shortly have pixinsight and so we can see what the results are like. 

Thanks for the info