How to attach guidescope to SW150PDS ?

[imakebeer]

Since the weather at the moment seems to be terminally cloudy I've finally turned my thoughts to how to attach a guidescope to my SW150PDS - advice from the SGL massive would be much appreciated.....

First pic below shows the OTA. Mounting options seem to be either to attach it via the finder shoe circled in red or piggy back on to the tube rings circled in green.

Second pic shows the bits I have:

• Altair guidescope
• Tube rings and standoff (?) supplied with the guidescope
• An alternative black finder shoe (?)
• A green Skywatcher (?) dovetail (?)
• Also various bolts I can use but they're cheap if I need more

So it's a question of whether I can use what I have or if I'm better to get some other bits?

1) Easiest option seems to be to fit the guidescope into its tube ring assembly and attach that to the existing finder shoe (it fits). But it seems like it might be handy to retain the optical finder scope???

2) I could replace the stock finder shoe with the rather more sturdy-looking black one. I'm somewhat reluctant to do this for fear of dropping the small nuts down the tube or knocking the secondary mirror but I can probably do it. But I still lose the optical finder scope.

3) I'm given to understand that we want the guidescope to be mounted as rigidly as possible so maybe piggy backing is the much preferred option...

• I'll need to rotate the OTA in its rings to avoid the focuser - not a problem.
• I think I can fix the spare green dovetail to the OTA tube rings but then what?
• I'm not sure I can then easily attach the guidescope tube ring assembly to the dovetail. At least, I can probably attach it but I'm not certain how rigid it would be.

So am I better off to source some extra bits for piggy backing, and if so, what? Or do I just take the easy option and see how I get on for now.

Thanks in advance 👍

[Ratlet]

Are you only using it for imaging?  You can attach the dovetail to the top of the 150pds tube rings then remove the guide scope rings from the guide scope and attach them onto the dovetail.  That how I did mine.  Just need the correct size/length of bolts.

You could use the finder scope attach and just mount the guide scope there, but you might get a bit of flex which could affect guiding.

[carastro]

I have been using the finderscope foot for donkeys years for the guide scope.  I have never had any flex with it.  Mine is in fact a converted finderscope.  I guess you need to make sure the foot fits tightly.   The only disadvantage l have found that being to one side the balance in Dec is a little lop sided, but doesn’t seem to affect guiding.   
 

Carole
 

 

Edited March 12, 2023 by carastro

[bosun21]

9 minutes ago, carastro said:

The only disadvantage l have found that being to one side the balance in Dec

You could buy an offset finder mount to rectify your dec balance problem.

[carastro]

To be honest l could slightly rotate the scope in the tube rings.  Just never remember to do that. 

Edited March 12, 2023 by carastro

[Ratlet]

39 minutes ago, carastro said:

I have been using the finderscope foot for donkeys years for the guide scope.  I have never had any flex with it.  Mine is in fact a converted finderscope.  I guess you need to make sure the foot fits tightly.   The only disadvantage l have found that being to one side the balance in Dec is a little lop sided, but doesn’t seem to affect guiding.   
 

Carole
 

 

My imaging paranoia stands corrected.  I'll give the finder foot a try.  Makes it a bit easier as I use my scope mostly for visual and the second dovetail gets used mostly as a handle (as is tradition).

[imakebeer]

2 hours ago, Ratlet said:

Are you only using it for imaging?  You can attach the dovetail to the top of the 150pds tube rings then remove the guide scope rings from the guide scope and attach them onto the dovetail.  That how I did mine.  Just need the correct size/length of bolts.

You could use the finder scope attach and just mount the guide scope there, but you might get a bit of flex which could affect guiding.

I would say using it mostly for imaging - I don't want to completely give up on visual hence I want to keep the visual finder scope ideally (plus I can see it being a useful backup).

I thought about doing as you say, attaching the dovetail to the 150pds rings, then attach the guidescope rings to the dovetail. The issue here is that the bolts for the guidescope rings are smaller diameter than the holes in the 150pds rings and the dovetail so there is potential for some play.

[Ratlet]

8 minutes ago, imakebeer said:

I would say using it mostly for imaging - I don't want to completely give up on visual hence I want to keep the visual finder scope ideally (plus I can see it being a useful backup).

I thought about doing as you say, attaching the dovetail to the 150pds rings, then attach the guidescope rings to the dovetail. The issue here is that the bolts for the guidescope rings are smaller diameter than the holes in the 150pds rings and the dovetail so there is potential for some play.

  I'd give it a try on the finder foot.

You'll need to source the correct bolts to attach it to the rings.  Can't remember what they are, but they might not be metric.  

[ONIKKINEN]

I would try it in the finder foot at first. If you start seeing suspicious star shapes but guiding reports everything is ok you have flexure and need to think of something else. But chances are high that wont happen so start with the finder shoe. The problem might not be with the connection between the guidescope foot and the finder shoe, but the tube under the finder shoe which might buckle and bend under gravity in different orientations of the tube. Not sure if that's a problem with the 150PDS but with my thin aluminum tube VX8 it was.

Balancing the tube is solved by rotating the tube in its rings so that the camera and guide scope both point towards the ground with the center of mass in the middle (so neither should point directly down).

[Padraic M]

I attached a second dovetail to the top of the tube rings. I don't have it to hand at the moment so can't show a photograph, but it did entail buying new mounting bolts for the dovetail plate.

You could continue to use the finder scope fitting. However there are two advantages that I get from using the dovetail ring - it's much easier to balance the whole assembly on the mount, and the second dovetail provides a handy carry-handle. The scope, complete with camera and guidescope, is surprisingly heavy!

[Enceladus Dan]

I made a bar from leftover aluminium I had, I drilled it to fit the top of the rings and mounted 2 finder shoes at the front. My Dew Heater controller fits behind using velcro and sits under the back of my guide scope. 

Clear skies

Danny. 

[Enceladus Dan]

Additionally I saw a post today where someone was trying to ballance a 72ED Pro with guidescope, and AsiAir. In the end they used perspex between the ring tops to mount the AsiAir further forward. Making balancing easier. 

I think 2 pieces of perspex in layers would be study and light for a guide scope to sit on.