Not quite 1.5 min down to 30 secs. The reduction is 2.52 actually and I rounded. So a 1.5 min exposure would be down to 36 secs and with the 60% wider FOV.
Buy a reducer first! It's one of the cheapest improvements you can make for your scope. Even visual viewing is more pleasing with the reducer in place. Think of the reducer and AVX mount as two separate issues. I don't think there is anybody that regrets buying a reducer for their SCT.
I have a Celestron and Astro-Tech f/6.3. The Celestron is something like $120 and the A-T was more like $70. Even though many say they are identical my Astro-Tech brings things to focus a bit sooner than the Celestron, so they aren't really "identical" but probably pretty close.
I purchased the Celestron first simply because I wanted a known quality brand. Aside from the slightly shorter focus distance for the A-T, which would mean a slightly shorter working distance of something more like 100mm, and IF they are all the same shorter focus and this is not a result of poorer quality control, then I'd say you could go with the A-T; because optically it seems fine.
One nice thing is that your 8SE gathers almost 2x more light than my 6SE, so with all other things being equal, I'd have to collect around twice as many exposures to get a similar signal as you can but mine will almost certainly have more noise as well.
I don't use the star diagonal when imaging because it doesn't allow for using more than one f/6.3 reducer and I don't need it when using the 0.5x alone to reach the zenith. However, when using just a single f/6.3 you could attach the f/6.3 to the back of the scope, the visual back to the reducer, the star diagonal to the visual back, then whatever you currently use to attach your DSLR to the visual back into the star diagonal. The path length of the Celestron 1.25" prism star diagonal that comes with the scope is reported to be 66mm. I strongly suspect your distance from the back of the reducer to the DSLR's sensor when using the star diagonal is going to be more than the recommended 105mm. The change in reduction, and I'm guessing (hoping?) any increase in coma, isn't that terribly strong with working distance so go ahead and try it. Your going to have somewhat more than the f/6.3 reduction (f/6 ??) and may have some noticeable vignetting that you can crop out if it's too bad. Using the star diagonal should get you more in alt before hitting the mount than having everything in a straight line out the back of the scope.
With all the extra weight sticking off the back of the scope you are more than likely going to have to push the OTA pretty far forward in the mount dovetail as possible to have the OTA being better balanced and the best chance at not having the camera hit the mount and restricting the alt you can reach. It would probably be a good idea to balance the whole OTA with everything attached on a pencil or other tube to find the new balance point and then mount the OTA assembly such that it is slightly back heavy if possible. If not then slightly front heavy. The main thing is to have some weight preloading the alt spur gear so the OTA can't do any see-sawing over the pivot point if too well balanced.
Also, if you haven't done so yet, adjust for the gear backlash. I'm pretty much assuming that you have done that. If by chance you haven't do a search on adjusting backlash and some very good information is contained in postings by a now deceased and very helpful person who went by the user name of "tel" or "Tel".
If you want to use your DSLR without the star diagonal then the good news is I think you only need the T2 extensions. Since I don't use a DSLR there may be a better way to do this that I don't know about. You'll still need the proper adapters for attaching your DSLR to the T2 and then a T2 to 1.25" adapter for mounting into the visual back; you likely already have those. Having all this stick out the back of your scope is going to limit your altitude to roughly 60o when not using a diagonal and you'll still have to pay attention to the OTA balance. I've found lots of things to image lower that 60o but it is rather annoying if something potentially interesting is above 60o and I can't get to it.
I purchased the set of T2s through Amazon...
You can definitely get some nice images of the smaller/brighter DSOs with a single f/6.3 and the 8SE but you need to remember this is not a scope meant for DSOs. Cancelling the wedge is a good idea and apply the money to something else. The AVX idea is still a good one too. But to be honest doing fast exposure lucky imaging can absolve the poorer SE mounts from a lot of sins.
As a final input I'd suggest thinking about doing EAA with a cmos imager dedicated for astroimaging/fast exposure photography and a laptop PC at the scope. The DSLR route is cheaper for sure but I quickly became hooked on now being able to do everything but the initial setup and take down remotely from inside a warm house. The 8SE can be a pretty capable EAA scope when setup properly. I just wish Rochester wasn't so darn cloudy. I can live with the light pollution.
Mike Swanson's "The Nexstar's Users Guide II" is a very good reference to have and not that expensive. I very much recommend it since you have an 8SE.
Oh, and by the way, welcome to the great money pit called amateur astronomy.
Edited by rnyboy, 09 April 2020 - 08:32 AM.