Celestron CPC 800 wedge with starsense

[Loki1978]

Hi all, 

I was hoping you could help with my new wedge. I've been imaging with an Alt Az mount for a while. A celestron HD wedge came up for sale so I bought it an eagerly mounted my scope. I'm having a real mare with alignment. I have starsense so I do an auto align and let that run. Then do a polar align first using hand controller to centre on a star to the south half way between the horizon and zenith. Then the next alignment is using the mount adjustments to centre the star again. In my mind this should be finished, but with starsense it prompts you to do an auto align once again. Once this completes if I try going to the same star its always off centre to the left, so far off it's out of field of view for my ccd. If I manually adjust the mount again without involving the hand controller my gotos seem ok. Am I expecting too much from this mount or do you think starsense it overcomplicating the procedure. In alt az my gotos were always good. The only issue I have at the moment is my ccd chip size is giving me a small FOV. Soon to be fixed with a reducer, but its making finding targets a real problem.

[Richie092]

Hi. Just getting in to this myself. What software are you using? CPWI?

[ollypenrice]

The wedges are inherently very difficult to align because they are not precision made. The result is that an adjustment in one axis causes an unwanted movement in the other. The only solution is to do it all in small, incremental adjustments and accept that it will take some time re-iterating the procedures. It helps not to loosen the locknuts too much. The closer you get to alignment the wiser it is to keep them moderately tight as you then turn the adjusters. With the amount of play in the system there is a wide gulf between what's supposed to happen and what does happen.

I would also ditch the software based approaches. Just use the classical drift method. That way you won't be worrying about the software complicating things, which it usually does. The DARV method of drift alignment is a great way to get close, and possibly close enough. https://www.cloudynights.com/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760  With the drift method you are not operating through a third party (the software) but interacting directly with what matters, the sky.

Olly

[michael8554]

PA is generally carried out first, only using the wedge controls.

Then Star Alignment only using the handset to centre stars, using the wedge controls messes up your PA.

Michael

[Loki1978]

Thanks for all the replies. 

I think I'm going to start leaving the tripod setup in the garden rather than spending ages trying to set it up every session. 

My alignment last night wasn't too bad. After an hour and a half imaging M66 went from centred to bottom third of the screen (I'm using apt) so something up with the alt adjustment I think. 

Richie, At the moment I'm using APT and Stellarium. I will have a look at CPWI.

Olly, I see what you mean about the mount. Azimuth seems pretty easy to adjust. But the Alt adjustment is extremely touchy. I'm an engineer by trade and I've been mulling over putting a microfocuser type adjustment on the Alt. Or even putting a polar scope in the middle of my C8 front plate.

 

Michael, I'll try to see if I can do PA first. I'm not sure the HC gives me the option. I think it forces an auto align, then polar align, then makes you do an auto align again. I'm guessing the last auto align is so that it can calculate the error.

[michael8554]

Further to what Olly says, I can make fine adjustment to Alt without loosening the lockscrews - wedges are that bendy.

Michael

[Cosmic Geoff]

I have a CPC800. You will not want to hear this, but you should have got a German equatorial and another C8 OTA (or other design of OTA) instead of trying to use the CPC800 on a wedge.  Wedges are okay for a permanently mounted SCT (witness their use in observatories like the one at the Open University) but not for one that is taken down at the end of each session. Forums have a number of accounts from people who have put a SCT on a wedge with great enthusiasm, then a year ot two later given up and changed to a German equatorial.

I also have a Starsense, used with a C8 SE.  It is great for speeding setup, but does not seem to be any more accurate in practice than a 2-star align with the basic Nexstar handset.  So far as I have been able to understand it, with an equatorial GoTo, so long as you have a rough polar alignment the GoTo should work okay (e.g. for visual use) but some image rotation deleterious to long exposure imaging will occur unless the mechanical pol;ar alignment is spot on.

I have tried deep sky imaging with my CPC800 SCT on short exposures, with poor results, and also with a 102mm f5 Startravel, which gives a wider field and delivers images with live stacking which are pleasing to me, at least.

[SaberJeff]

You need an equator.

[Loki1978]

Geoff, I recently got back into astronomy and I kinda went out and bought something familiar to me, I then started going down the imaging route and soon realised the equipment I have is not really suited. 

I do have a williams optics zenithstar sitting on the shelf here but no mount. I'm aiming to buy an eq5 or 6 at some point. I think when I do I will take the wedge off of my cpc and use it for visual. Then buy a c8 ota for the equatorial if I really want that much focal length. I would love a RASA but £££ Actually I did notice you can buy a hyperstar conversion kit. Has anyone tried one?

Edited March 9, 2021 by Loki1978

[SaberJeff]

I use cpc1100 to see and photograph planets, and I use ZSI cameras instead of deep space objects. I'm going to buy an avx equator and a 70 apo refractor.

[Loki1978]

Jeff, Cool sounds like a plan. I can't wait to get a mount for my refractor. I haven't imaged in widefield yet. I've always had too much magnification with the cpc 800.