I followed suit and got up early to capture this image. To be honest, tracking wise, it's far from my best set of subs I'm happy with how the image came out but I'm also fully aware of what went wrong and what I'll be doing next time.
Hi Ryan, Your focus seems to be off. How are you focusing? Does your 5D have "Live View"? If so it makes focusing easy by enlarging stars by either
5 or 10x.
I have attached a pic of similar scale to yours to illustrate how your stars should look.
You are up against it using an f/10 scope;for comparison the attached image is a single 10 sec frame using ISO 1600 with an 8" f/5 scope.
raymo
I focus with a bahtinov mask. My 5d is a Mk1 so it doesn't have live view but I do spend a lot of time taking focus shots and viewing them before I start my sub sets.
This particular set up suffers a lot from coma and vignetting at the moment and this object went way off centre during the session. Hence my comment about knowing it wasn't a great set. I'm still pretty happy with the photo though given where I've come from.
Do you have a pic of yours for comparison from an f10 SCT unguided so I can see what mine should look like ? So I can compare apples with apples ?
Here's my pic Ryan, I checked the details and was a single sub at ISO 3200 for 80 sec with no editing with the pic.
Are you doing darks? I noticed when I use a high ISO I get a lot of noise in the pic. I think me having a slower f helps have a darker pic, not sure.
I think also living somewhere that the skies don't resemble Times Square also helps with a darker pic too !
I do use darks but I've learned to be a little decerning with them because I find I lose a bit of the detail in the shadows when I use too many. It's all a balancing act and I'm still learning so much.
Definatly on my list of things to buy is a focal reducer / field flatterer.
Notice though, between your first pic and your second with the reducer, you have to start being careful with the ISO. The core of the nebula has become blown out. Wider field = more concentrated light.
Sorry, I sold my last SCT[8"] years ago. but maybe someone else will post
an image for you. Maybe the lack of sharpness is a stacking artifact; are
your individual frames sharp? I posted my image mainly to illustrate how the stars should look [focuswise], not how bright the image should be.
raymo
Definatly on my list of things to buy is a focal reducer / field flatterer.
Notice though, between your first pic and your second with the reducer, you have to start being careful with the ISO. The core of the nebula has become blown out. Wider field = more concentrated light.
yeah I didn't change the ISO for that shot and it was a 20 sec exp
The dynamic range of M42 is so great that you cannot do a single image of
it that shows most or all of the nebulosity without blowing out the core,
regardless of what ISO is used. You need to stack a mix of very short subs
that correctly expose the core, and long subs that capture most or all of the
nebulosity, and use layers, masks etc to end up with an image that
preserves the core.
I have attached an image to illustrate my point. I took it years ago, all longish subs so
that most of the nebulosity is shown, but the core is blown out even though
I reduced the highlights in the image to the minimum possible without
stuffing up the image. The core was initially incredibly blown out.
raymo
Last edited by raymo; 26-08-2018 at 01:45 PM.
Reason: add image and more text
Sorry, I sold my last SCT[8"] years ago. but maybe someone else will post
an image for you. Maybe the lack of sharpness is a stacking artifact; are
your individual frames sharp? I posted my image mainly to illustrate how the stars should look [focuswise], not how bright the image should be.
raymo
I went back to my subs and checked and they are considerably sharper. I'm trying a different stacking method now and we'll see. Otherwise, at this stage, I'm still convinced it has to do with how much and how far it drifted off censer into my coma and vignetting zone
I'm happy with how the image came out but I'm also fully aware of what went wrong and what I'll be doing next time. 
