This is what I use on my Tal 200k FL 2000mm. A 100mm diameter 340mm FL achromat in a PVC pipe tube held with six nylon screws. For guidestar selection just laterally move the the magnetically mounted webcam until you find a guidestar (always works). There is no flexure as the guidescope does not move. The whole thing is very light. See pics below. Also a pic of a 'normal' telescope version.
Yup, I looked at that one in Bintel a week or so back - seems good but mounting it is the problem. The 200 rides on a dovetail bar on the Sphinx, if I switch to rings and over under mounting this I will not balance and exceed the weight limits of the mount).
Quote:
Originally Posted by [1ponders]
I can't see why you wouldn't be able to pick up the OTA without the mount.
Normally I'd recommend Losmandy guiderings but those plus the guide bar would probably come in a 2 or 3 kg on their own.
What is your limit weight wise, for rings and guidescope.
Sphinx can handle 10Kg - VC200L is 6Kg, Canon20d is 0.7Kg. Ideally the guidescope and mounting system is about 1Kg.
Quote:
Originally Posted by [1ponders]
Bert's option looks the go. Do away with the guiderings altogether
Hmm 1 kg is going to be pushing it. Maybe some sort of side by side mount to keep the center of gravity as close to the head as possible. But then your will be adding extra weight in the form of dovetails and mounting saddles. I've just recently bought a 76 mm copy scope that shouldn't weight more than a kg or so (I could weight if you want). There might be a few of those around on the astromarts somewhere.
I can well understand you dilemma John as I was going through the same issues with trying to mount an 8" sct and the Orion 80ED on my Losmandy GM8. If you haven't read any posts in the pic of your equipment thread I made mention of your counterweight shaft attachment. I really wanted something like that to solve my problems. I eventually went for a side by side setup and found a small 60mm refractor to use as a guidescope rather than the 80ED. It was pushing the limit photography wise (not as much a you are though) but at least everything was in close to the head. I also had more counterweights made to shift everything up the CWS, again to bring as much weight in close to the head as possible. My solution in the end was to buy a G11. I know but I couldn't help myself
You have an interesting situation happening here, I would normally say to people don't exceed 2/3 the capacity of the mount, only having 1 Kg to play with leaves little room to play with. I would be loath to place another OTA above because of centre of gravity issues and having to place weight on the countershaft further down which introduces it's own problem's.
The only other solution I can think of is an Off Axis Guider, I have never been a fan of these because of the small pick-off mirror although there are some around these days that can be rotated. I suppose a problem is going to be the LPI and selecting a guidestar that is bright enough.
I feel you are going to be very limited although Vixen probably understate the mount capacity a little.
My solution in the end was to buy a G11. I know but I couldn't help myself
And that G11 is just not going to happen for me...
I can't see how to do side by side without blowing the weight limit, I think it must be over/under, one idea is to mount under the main OTA witht he guidescope upside down at the front by attaching to the existing dovetail rail...needs a short tube of course - anyone done it this way?
JohnH is there a reason you aren't using the counterweight shaft fitting that's in your equipment image as the mounting for your guidescope, and use it to replace some of the counterweights?
Well yes I can use that, but it is really intended for a camera - if the tube extends beyond the shaft centreline there are many positions where the guidescope can collide with the tripod or mount. Works ok when I can use it (ie > 15 deg from SCP)
I can see one real bad issue mounting it forward on the dovetail rail, you are going to have serious balance issues, you will need a lot of weight at the rear to balance.
You have an interesting situation happening here, I would normally say to people don't exceed 2/3 the capacity of the mount, only having 1 Kg to play with leaves little room to play with. I would be loath to place another OTA above because of centre of gravity issues and having to place weight on the countershaft further down which introduces it's own problem's.
The only other solution I can think of is an Off Axis Guider, I have never been a fan of these because of the small pick-off mirror although there are some around these days that can be rotated. I suppose a problem is going to be the LPI and selecting a guidestar that is bright enough.
I feel you are going to be very limited although Vixen probably understate the mount capacity a little.
JohnG
Pretty sure you are right there Vixen will be conservative - there are users out there with 10" tubes on this mount....but I want to stay as light as I can. I also have the incompatible desire to have a high quality guidescope that I could use for widefiled imaging and as a grab and go...looking at and ED66 perhaps?
I started this saga with the Vixen OAG for exactly these weighty reasons, unfortunately it turned out that the OAG could not be used with the Vixen FR thus rendering it all but useless. I have tried (without luck so far) to identify a compatible OAG that people rate - the closest is the Lumicon Giant OAG but this needs customisation....then as you point out the LPI sensitivity is an issue, I suppose using as DSI as the guidecam would fix that - if this is the best path to take, any advocates of the OAG method out there care to comment?
You have a bit of a problem, no doubt about that, I have just completed a week of testing an LPI with GuideDog and K3CCDTools 3 against the ST-4 I have. The gist of the results were that the LPI needed fairly bright stars in GuideDog abd in K3CCD it would track on alot fainter stars. The ST-4, well old technology but beat the pants off the LPI.
Maybe K3CCD is the answer, only thing I din't like was it's performance on bright stars, very eratic.
Have you seen any independant review on the Taurus Tracker JohnG. I thought about the idea of one when I had just the GM8 but I had trouble finding a decent review of it. I really liked the idea of it, but previous experience with the Meade OAG turned me off OAGs in general.
I actually have an older model down here and have tried it although, like you, I don't really like using an OAG. There are 2 models now, you can see them here: http://www.taurus-tech.com/
There are a couple of members on the Losmandy and Gemini Groups that do use them and they are getting excellent results and swear by them.
![[1ponders]'s Avatar](../vbiis/customavatars/avatar45_9.gif){kind=avatar}
I know but I couldn't help myself
reasons, unfortunately it turned out that the OAG could not be used with the Vixen FR thus rendering it all but useless. I have tried (without luck so far) to identify a compatible OAG that people rate - the closest is the Lumicon Giant OAG but this needs customisation....then as you point out the LPI sensitivity is an issue, I suppose using as DSI as the guidecam would fix that - if this is the best path to take, any advocates of the OAG method out there care to comment?
