Guiding issues with 130PDS and guidescope. Is an OAG a viable option?

[billyharris72]

Hi all:

I've struggled a bit with getting a guidescope to work well with my 130 PDS/ HEQ5 setup. I've used three arrangements (all with a 120m as the guide camera).

1) QHY 30mm f4 guidescope, mounted in the finder shoe. Works well, but is a little short so pixel scale / performance could be better. Probably the best setup so far.

2) Skywatcher 50mm ED in the findershoe. Impossible to balance the scope in DEC with this setup - massively front heavy. I suppose I could put a counterweight of some sort at the back.

3) Skywatcher dovetail bar on top of the tube rings with an ADM clamp and the 50mm guider mounted on that. Worst setup by far - just terrible. First, it flexes. Second, the guidescope points straight at the camera unless I rotate the scopein the tube rings so it is out of the way. The scope is now out of balance in DEC (put it in parked position and loosen the clutch and it will move in the direction of the camera).

Of these, option 1 is certainly bearable, and one improvement might be to try a guide camera with smaller pixels (maybe the ASI290MM). The other option I was considering was using an OAG. It would probably be the lightest and tidiest option, and it's cheaper. Does anyone out there have any experience with this combination? My main concern is with the illuminated field of the PDS. Will it be possible to illuminate the guide camera without having the prism protrude into the main imaging area?

Thoughts and experiences much appreciated!

Billy.

[almcl]

If you can't eliminate flexure any other way, then an OAG will certainly help.  I moved from an adapted 50 mm finder scope to an ST80 (ghastly thing, as others have observed, the appalling focuser flops about all over the place) and then to a camera specific OAG and the improvement in round stars was instant and dramatic.  

Not sure what camera you are imaging with, but my Canon OAG keeps the prism well clear of the light path:

[alacant]

52 minutes ago, billyharris72 said:

parked position

Hi. Remember that DEC must be balanced both longitudinally and laterally. Everyone forgets the lateral (turning) balance. To help balance, the camera should be placed so as to give the lowest centre of gravity. On the 130, this is with the camera hanging vertically downwards when parked N-S.

Guiding: an OAG is lighter, gives the best stars (by far) and all but eliminates flex.

HTH.

 

 

[billyharris72]

10 minutes ago, alacant said:

On the 130, this is with the camera hanging vertically downwards when parked N-S.

Interesting, and makes sense. I've tended to the exact opposite (pointing up) but down does seem much more stable thinking about it. That might even work with the guidescope setup, as it would be opposite to the guide. I'm really tempted by an OAG though. Do you use one with that DSLR? If so it should cover my chip no problem.

Billy.

[alacant]

10 minutes ago, billyharris72 said:

Do you use one with that DSLR?

Yes. You can see it in the photos I posted. I think @almcl used the same OAG as I.