Losmandy GM8 questions

[Vermin]

I'm considering purchasing a Losmandy GM8 and was wondering if the polar alignment scope is necessary as it does not come standard.

For visual use a rough alignment using a corrected compass and known latitude should be ok, and for imaging a drift align is necessary anyway.

Also how important is it to have the OTA aligned with the polar axis? How could this be done without the polar alignment scope?

The universal dovetail plate that fits a Televue TV101 does not seem to have any method of adjusting the OTA alignment anyway. Would I be better off with tube rings?

Thanks,

V.

[JohnG]

I have had a GM-8 for some 5 years now and have not used the Polar Alignment Scope, I have never thought of it as a necessary option although a lot of people do use one, in the field I do as you have said, rough then drift if necessary. I asume that you are going to use the Universal Dovetail plate, no there is no way of shimming that when it is in the saddle, what you do is shim the actual tube mounts with thin bits of brass or similar so probably tubes rings are the go, might I suggest Parallax Instruments rings, they seem the best. As far as aligning with the Polar Axis, the TV101 has a pretty wide field of view so unless you are going to align with a crosshair eyepiece you are not going to be all that far out.

Hope this helps a bit.

JohnG

[JohnG]

Sorry, meant to ask, is this going to be with Gemini.

JohnG

[Vermin]

Thanks for your help John, very informative.

I can't afford the Gemini at this stage. However StellarCAT make a second scope option for GEMs for their ServoCAT goto that I may be able to afford (I have a ServoCAT on my DOB that is very easy to remove/reinstall). I'm going to investigate this further.

The TV101 does have wide FOV, but less so if doing eyepiece projection, and I can't see how it could be shimmed in RA as the two mounting bolts are in line along the length of the OTA. Filing out one of the dove plate holes perhaps?

It would be nice not to have to use tube rings as the OTA would still fit in the case for transport with just the universal dovetail plate attached.

Thanks again.

[JohnG]

Hi Vermin (nice name)

No need to file out the holes, just move the saddle to it is in it's correct position and reset the Dec circle, I personally don't think that the tube will be out very far, I think we would only be talking thousands of an inch at the most, with my Tak I just use the Tak Clamshell attached to a BT plate and I have never had any dramas.

I still think, even with eyepiece projection, the field of view is still going to be quite large and can compensate, other users might chine here with their thoughts.

Cheers
JohnG

[Vermin]

No worries, I'll just go with the universal dovetail plate for now. Thanks for your help.

As for the name... it's a leftover from another forum I was trying to think of a username for while watching the movie Timebandits (it's one of the characters names).

Regards,

Tom.

EDIT: I forgot I'll need another set of mounting hardware and encoders for the ArgoNavis as well as the Servocat hardware. This has pushed it beyond my budget (and is more expensive than ordering Gemini with the mount too, I think). So no goto for now.

[JohnG]

If you are going to get encoders, make sure you get the 8000+ tick, not the old 4000+ tick. An absolute must is the Gear covers, you will eat your cables and fingers if you dont. ( learnt that from experience, it hurts)

JohnG

[[1ponders]]

If you're going to get encoders then maybe think about getting an Argonavis with it's new TPAS system. Have a chat to Gary K that might solve the problem of misalignment.

[Vermin]

Thanks for the advice guys, but as I said above I will not be able to afford a second set of encoders for my AN.

The price listed on the Wildcard website for another set of encoders and mounting hardware for the GM8 is $500+.

[[1ponders]]

Yeah Losmandy encoders aren't cheap. I'd like another set to use on my GM8 :sad: