[RCC] M45 - The pleiades

I can't say it's a bad image given the equipment! 


So, a few things I'm noticing:

- the image still a bit noisy. Have you been using any darks/bias/etc to deal with that? as you didn't list your darks and such here. Did you dither? Some of the nebula and dust is getting a bit lost in the noise and the star reduction. As most stars seem to have a bit of a dark ring or area around them if I start looking in really close, so perhaps look at the star reduction methods you have used.

- speaking of the stars
Star shapes could be a bit better, most are pointing left and up. Which could mean tracking issues. 
So perhaps you could look into your polar alignment and/or the exposure times.

All the bright stars around Pleiades have been reduced and dimmed a lot, + all the bright yellow stars have lost all of their colour; making the star field seem a bit flat. No idea if that is a filter thing? or that the exposures at F2.8 were too long to get good colour in the stars.
Because there is a lot of nice colour in the surrounding stars. so you could consider making separate short exposures for a star-layer and blending everything together.



But; 

- What might be working against you too is the camera and lens that you're using.
The camera has a pixel size of 6.56µm. Which is quite big.. which means that at 200mm you are significantly under sampling your image. 

Native Focal Length / F: 200mm / F2.8 
Ideal Resolution : 0.67" - 2" arcseconds
Resolution: 6.77" arcseconds per pixel
Sampling: Significant Undersampling 


So all the little bits of detail in the stars and dust, are basically smaller than the pixels of the camera.. this limits how much detail and resolution you can get from an image because the pixels simply aren't small enough to capture those details..
You can "fix" that by using "Dithering" and "Drizzle".  - And I believe you can use the app of the star adventurer to dither in there, IF you have your canon attached to the star adventurer with a shutter release cable. So if you're not doing that already, it's worth looking into. As it deals with noise too.



It's definitely not a bad image though!

I recollect that when I tried Adam Block’s Star reduction technique, it worked very well up to a certain point where I started getting dark rings around stars.  I would monitor my progress with the technique so that I did not over do it. I would use it up to the specific point where the dark circles just began to appear so as  to maximize its value.

Didier Kobi:
I have also the 70-200L mkII and the 100-400L mkI and I have done some quick tests compared to using prime lenses and I think that using f/2.8 on the 70-200 @ 200mm doesn't help if you want details.

The 100-400 mkI @ f/5.6 is basically unusable for astrophotography and while the 70-200 mkII seems quite a bit better, it is still not that good for astrophotography I think. If you look at the stars, they are not nicely round and show some coma: this blur is obviously also present in the nebulosities.

I don't know if it is the main reason, but I would say that the 100-200L should be used at f/4 or even f/5.6 to get a decent result.

... and the 100-200 mk I is catastrophic - at least my sample ...