neilmac

22 hours ago, noah4x4 said:

I tend to use my cooled Atik Horizon with Hyperstar. I think that conbination is absolutely awesome and at f/2 images form near live as photon capture is 25x faster than at f/10. But an issue is that whilst the FOV at f/2 is great, some objects are small and ideally need f/4 or f/6.3 (albeit that requires longer exposures/integration time). F/6.3 is where I employ my ZWO.

I bought the ASI294mc (uncooled) because the Atik Horizon is 12.5cm long and it is impossible to gain rear end clearance on an Evolution. However, with 105mm back focus required behind a 6.3x Celestron Focal reducer the (non-cooled) ASI294mc fits perfectly with a fraction to spare using a 50mm T-Adapter plus Baader Varilock. Cooled cameras and Alt-Az are typically a clearance problem unless you employ a wobbly visual back and diagonal combination that introduce all manner of issues.

However, I have tried the ASI294mc on Hyperstar and frankly, have not noticed much difference compared to the Horizon except back focus is critical. It needs 4mm less spacing, hence I had to get Starizona to ship a different spacer ring to fit between Hyperstar and my filter slider as you do need to pair Hyperstar with OTA plus Hyperstar connection with each Camera (it helps that back focus in the ZWO range is commonly 17.5mm). 

Frankly, I am more of an EAA observer than Astrophotographer. Vignetting, coma, undersampling (etc) simply doesn't trouble me and as long as I can observe my primary target I just don't notice such aberations. But if it worries you, I am not convinced that any imaging at f/2 or f/4 will satisfy you and you will probably be better served buying a £5,000 high quality GEM mount and pursuing long exposures at (say) f/6.3. Using an extremely 'fast' scope probably infers acceptance of some compromise. For example, both Atik Horizon and ZWO ASI294 have sensors larger than the current NightOwl image circle and some vignetting is inevitable. Similarly, I have tried stacking two focal reducers. Works well, but you need to crop the corners. 

 

 

Thank you for your detailed response. I’m only interested in EAA too. Lots of queries answered, in particular the use of the non-cooled version of ASI294 at the rear end makes sense now! I’m completely new to all things camera related and in fact have not had my C8 edge HD for much more than 6 months. Would you say cooling is less of a requirement for EAA?

On 21/06/2020 at 09:28, noah4x4 said:

I use Hyperstar at f/2 and Celestron Focal Reducer at f/6.3 with my 8" Evolution and Atik Horizon and ZWO ASI294mc. Both work great. The only issue with Hyperstar is the removal of your secondary mirror means wide FOV, but loss of magnification. The issue at f/6.3 is it is much slower than at f/2.  No solution is perfect. The NightOwl might provide a decent compromise.

I too am awaiting availability of the NightOwl at f/4. However, my understanding is that vignetting is likely, especially with larger sensors. That is certainly true of another option I have tried which is the use of dual Celestron x0.63 FRs. But if you crop the corners to delete the vignetting, then stacking dual Focal Reducers is a possible option. 

 

 

How are you finding your 8” evolution + hyperstar + asi294 combo? 
Ive got the 8” evolution and looking to purchase hyperstar and most likely the asi294.

however, going by the online astronomy tools calculator, it suggests that the asi294 would be under sampled in this combination. Is this something you’ve experienced in reality? I’d be keen to hear your experiences with this setup.

Also, using the asi294 with the Nightowl reducer - would there be sufficient clearance at the mount when the scope is near zenith?

3 hours ago, Bribrum said:

Thanks pal. We can not be too far apart. I’m in Fernhill heath. Those links are very helpful. Woken by the dog at 3am today and was able to see both Saturn and Jupiter from the front garden. Need to get my scope on them both ASAP. I’m looking to drive out  somewhere very soon to view them whilst they are available 

Hi, I’m in Fernhill Heath too and I’m also finding that light pollution seems to be getting worse. So much so that I’m considering EAA to be able to see more from my back garden!

In terms of local dark sites, I’ve spoken to one of the local farmland owners in the area who owns a couple of decent looking locations to observe from. Once lockdown is over I’d like to try one of theses locations out and will report back. It’s in the area between Porters Mill and Hadley.