Skywatcher AZ EQ6 GT - guider on counterweight side?

[Tommohawk]

Ive just noticed that the AZ EQ6 GT has an adaptor on the counterweight side to attach a second scope, ostensibly for use in AZ mode. But wouldn't this lend itself well to the mounting of a guidescope in EQ mode? 

I guess this wouldn't be much help for those using OAG, but if using a guidescope it would free up some payload. Probably wouldnt work at northerm latitudes as the guide would foul the tripod, but in UK should be OK. 

What would be good is if this could be applied to s smaller mount for travel purposes. I know there are adaptors to put guidescope on the CW side but look a bit wobbly.

Any ideas on this?

[D4N]

On smaller mounts the counter weight shaft is unlikely to rotate with the Dec axis so this wouldn't work.  It could work for guiding in RA only though and would be the optimal way to do it on the likes of the star adventurer.

I can see the benefits of doing this if you have a mount that is designed for Az and eq use, I'm a bit far north for this though at 64°

[Tommohawk]

4 minutes ago, D4N said:

On smaller mounts the counter weight shaft is unlikely to rotate with the Dec axis so this wouldn't work.  It could work for guiding in RA only though and would be the optimal way to do it on the likes of the star adventurer.

I can see the benefits of doing this if you have a mount that is designed for Az and eq use, I'm a bit far north for this though at 64°

OK I sort of assumed that the CW shaft rotates with Dec on all mounts so that's a good point. 

[DannyLee]

Hi,

this gives me an idea, why not fabricate a mount for a guide scope that sits on the fixed balance weight bar on a bearing, and then have a short fixed shaft to connect the guide scope to the main scope dovetail?  This would allow the use of a decent scope such as my 127 Mak for guiding, ideally the guide scope would need to be short for the mount fouling issue, but I think that might work. Two scopes on the same mount for no weight gain, seems worth pursuing to me..

Dan

[Stu]

26 minutes ago, Tommohawk said:

OK I sort of assumed that the CW shaft rotates with Dec on all mounts so that's a good point. 

It does on the AZEQ6 so the idea seems possible as long as the second scope stands no chance of fouling the tripod. On a pier it might work?

[Tommohawk]

 

48 minutes ago, DannyLee said:

Hi,

this gives me an idea, why not fabricate a mount for a guide scope that sits on the fixed balance weight bar on a bearing, and then have a short fixed shaft to connect the guide scope to the main scope dovetail?  This would allow the use of a decent scope such as my 127 Mak for guiding, ideally the guide scope would need to be short for the mount fouling issue, but I think that might work. Two scopes on the same mount for no weight gain, seems worth pursuing to me..

Dan

That's a nice alternative, but my instinct is that anything coupled via a bearing and a strut would suffer some flexibility.

Going off on another tangent, it might be possible to mount a short guide scope on the underside of the main dovetail - would need the main dovetail to be quite long though. This wouldn't be as effective as putting it on the CW side but would be better than adding to the main payload.

I guess the main thing with the AZ - eq6 is that the counterweight mount seems tailor made for the job. See here.

[Tommohawk]

51 minutes ago, Stu said:

It does on the AZEQ6 so the idea seems possible as long as the second scope stands no chance of fouling the tripod. On a pier it might work?

Agreed, a pier would be better.

[Tommohawk]

On 9/19/2016 at 13:58, Stu said:

It does on the AZEQ6 so the idea seems possible as long as the second scope stands no chance of fouling the tripod. On a pier it might work?

Just a belated follow on thought! The AZ EQ5 version has just such a pier, and also has the scope mount option on the counterweight side. The AZ EQ 5 version is also lighter than the HEQ5 at 7.7kg, and the pier/tripod 6.1kg - it folds up nicely too. But still a bit heavy for air transport.

Now if they only did an AZ EQ3.......

[Zakalwe]

The guidescope and camera needs to be tightly coupled and rigid to the imaging scope. Any movement that's seen by the guidescope that's not seen by the imaging scope, or vice-versa, will lead to bad guiding. Hanging the guidescope off a long thin counterweight bar at the opposite end of the system form the imaging scope seems to be the exact opposite of "tightly coupled and rigid". In addition, the guidscope would be highly likely to hit the pier when imaging of slewing.

I've got to ask the question: Why? Mounting a guidescope on the imaging rig can be achieved with very little more than a couple of tube rings bolted to the main OTA rings. Why try an invent a sub-optimal solution? It sounds to me like an answer looking for a question.

 

[alexbb]

I already tried on the AZ-EQ5 what you asked and it worked OK for 1 minute subs. For 2 min, I started to see some differential flexture, for 5 min it was well visible. That was with the 130P-DS on top and 102 StarTravel below. I could have made it more rigid, perhaps, but I wouldn't recommend for longer subs. I also believe that I could have lighten the load by using a shorter/lighter guidescope and a counterweight, but then I could have just put the guidescope on top. Also, I'm at 45 deg north and the mount sits on a pier.

HTH,

Alex

[Tommohawk]

9 hours ago, Zakalwe said:

The guidescope and camera needs to be tightly coupled and rigid to the imaging scope. Any movement that's seen by the guidescope that's not seen by the imaging scope, or vice-versa, will lead to bad guiding. Hanging the guidescope off a long thin counterweight bar at the opposite end of the system form the imaging scope seems to be the exact opposite of "tightly coupled and rigid". In addition, the guidscope would be highly likely to hit the pier when imaging of slewing.

I've got to ask the question: Why? Mounting a guidescope on the imaging rig can be achieved with very little more than a couple of tube rings bolted to the main OTA rings. Why try an invent a sub-optimal solution? It sounds to me like an answer looking for a question.

 

Thanks for that.

Perhaps not surprisingly, I do realise the potential problems of poor correlation between the guidescope and the imaging scope! The counterweight bar in this case is 18mm steel, so not too flimsy hopefully. The manufacturer suggests its OK for a second scope of 15kg -  of course their intention is for visual only, but we're only talking about 2kg or so. As you may know, Geoptik produce a counterweight adapter for just this purpose, so its not completely unprecedented.

I think I recognised the potential issue of fouling the pier in post #1, but looking at Alex's post it does seem like it feasible. Admittedly he's at 45 deg, but then he's using a 102 which is a bit of a monster for guiding.

With regard to the purpose, the idea is simply to reduce the overall weight of the rig to improve portability and performance. In the past I've piggybacked the guidescope on the main OTA as you suggest, but 2kg of scope/rings and camera at that radius needs ~2kg increase in the counterbalance weight. With a flight allowance of maybe 15kg that's critical.

From a performance point of view, the less weight that has to be shifted around the better, so reducing overall weight has to be a plus. Transferring weight to the CW side is something which Vixen and Ioptron do exactly for this reason. BUT I completely agree there is s significant potential problem with flexure.

TBH I think even the lighter AZ EQ5 would still be too heavy for my purposes so it may be immaterial.

9 hours ago, moise212 said:

I already tried on the AZ-EQ5 what you asked and it worked OK for 1 minute subs. For 2 min, I started to see some differential flexture, for 5 min it was well visible. That was with the 130P-DS on top and 102 StarTravel below. I could have made it more rigid, perhaps, but I wouldn't recommend for longer subs. I also believe that I could have lighten the load by using a shorter/lighter guidescope and a counterweight, but then I could have just put the guidescope on top. Also, I'm at 45 deg north and the mount sits on a pier.

HTH,

Alex

Alex thats really useful. Apart from anything else its nice to know its not such a crack-pot idea and someone else has tried it!

As you say a smaller guidescope would doubtless improve things, but equally you're right in saying that the lighter it is the less issue there is with the counterweight. I was thinking of the 70mm Orion multi use scope  (though I'm not mad on the ring mounts - too close together) which would be about 1kg including camera. So mounting this on the CW side would save only about 1kg - maybe significant from a flight bag perspective.

I'm still try to work out what would be practical. I think I'd use the 300mm camera lens which works well at F2.8, so 4 minute subs might be OK assuming a lighter guidescope helps.

Can I ask a question please? Can you mount the head straight onto the tripod without the pier/riser? I'm just thinking this would save weight, although then of course we're back to the guide potentially fouling the tripod. Might be OK with a 70mm scope using a 90 deg diagonal.

[brantuk]

2 hours ago, Tommohawk said:

I do realise the potential problems of poor correlation between the guidescope and the imaging scope! The counterweight bar in this case is 18mm steel, so not too flimsy hopefully

For guiding it's the differential flexure you have to beware of. The c/w bar may be strong but it's not always held rigidly in place enough for the weight it bears and can potentially move. Zakalwe's suggestion that the two scopes need to be tightly coupled is entirely sound. Hth

[Zakalwe]

If weight reduction is the goal then I would try an OAG. OK, it will introduce it's own set of problems and compromises, but it is significantly lighter than a separate guidescope and counterweights.

[alexbb]

13 hours ago, Tommohawk said:

Can you mount the head straight onto the tripod without the pier/riser?

No

[Tommohawk]

On ‎17‎/‎10‎/‎2016 at 21:18, brantuk said:

For guiding it's the differential flexure you have to beware of. The c/w bar may be strong but it's not always held rigidly in place enough for the weight it bears and can potentially move. Zakalwe's suggestion that the two scopes need to be tightly coupled is entirely sound. Hth

Agree the clamp may be the weakest link

On ‎17‎/‎10‎/‎2016 at 21:36, Zakalwe said:

If weight reduction is the goal then I would try an OAG. OK, it will introduce it's own set of problems and compromises, but it is significantly lighter than a separate guidescope and counterweights.

Yes as you say OAG should be the way forward. Trouble is with camera lenses there is little room in the train, especially as I want to move over to mono with filter weheel at some point.

On ‎18‎/‎10‎/‎2016 at 08:34, moise212 said:

No

Shame!

[wornish]

I tried this when I first got my AZ-EQ6 and you do get problems with the guide scope potentially hitting the tripod legs so it does limit where you can point your scope.  I quickly changed to the traditional approach of mounting the guide scope on top of the main scope.

[Tommohawk]

3 hours ago, wornish said:

I tried this when I first got my AZ-EQ6 and you do get problems with the guide scope potentially hitting the tripod legs so it does limit where you can point your scope.  I quickly changed to the traditional approach of mounting the guide scope on top of the main scope.

Ok thanks, so looks like that may be iffy. That said the AZ-EQ5 variant has a short pillar on the tripod so possibly a bit more clearance.