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Istar 6 inch F/12 Equatorially Mounted Achromatic Refractor


John

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My big Istar refractor project has been rumbling on for ages while I try and sort out a suitable mount for this long and heavy tube. 

Having tried a heavy duty alt-azimuth approach (Bray Tablet Mount on the Meade Giant Field Tripod) I decided that a driven mount would be a better approach to keep the need to touch the scope to a minimum. I've been determined to keep the mounting arrangements within a budget that is broadly equal to the cost of the optical tube so I've gone for a non-GOTO EQ6 mount mated with the Meade Giant tripod via a custom adaptor plate. I assembled this setup for the first time this morning so I thought I'd take a few photos while I got my breath back from bolting it all together !

It's difficult to convey a sense of the scale of the scope in these snaps so for reference, the top end of the dew shield is about 9 ft from the ground in the last photo, the mount saddle at around 6 ft 6 inches. Carry out and assembly takes about 20 mins at the moment but that will improve as I get used to moving these heavy pieces of kit around. The overall weight of the setup is about 150 lbs. It's no "grab and go"  :rolleyes2:

It's a bit of a crazy dream really - a modern incarnation of a classic Victorian instrument perhaps ?

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Looks fantastic John. I think the minimal touch approach makes sense and applies equally to my 6" f11 dob which is in many respects a similar beast and I built an equatorial platform for exactly the same reason. what a beast!

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A fine long FL 'frac deserves an equally fine equatorial mount. I'm thinking brass and steel with big worm wheels and engraved setting circles..... :smiley:

But in the meantime a NEQ6 will do just fine  :grin:

Ye gods! I've just seen how many counterweights you've got there  :eek:

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Nice one John that looks to be a well capable mount and tripod solution. I know what you mean re conveying the size of these scopes, even my 4" F15 business end once its on the Cooke mount and tripod stands 8 and a half foot off the ground when pointing up. Al the better for keeping the objective out of all that nasty warm air near the ground. And who needs goto anyway :grin:, Im refurbing the setting circles on the Cooke Mount to relive the Victorian observing experience

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Thanks for the comments and further "Victorianisation" suggestions folks  :smiley: 

I've only looked through the scope briefly on a much less suitable mount but it's performance seems very promising.

Nice one John that looks to be a well capable mount and tripod solution. I know what you mean re conveying the size of these scopes, even my 4" F15 business end once its on the Cooke mount and tripod stands 8 and a half foot off the ground when pointing up. Al the better for keeping the objective out of all that nasty warm air near the ground. And who needs goto anyway :grin:, Im refurbing the setting circles on the Cooke Mount to relive the Victorian observing experience

Thanks Phil.

Sounds like your 4" F/15 project is still moving onwards and upwards. We missed you and the scope at the SGL9 star party  :smiley:

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Lovely setup John, glad you are getting where you want it to be finally. I do think the driven mount option is the way to go, as I've mentioned elsewhere, being able to concentrate on the views, waiting for moments of steady seeing is much easier without having to nudge frequently.

Looking forward to hearing more about your 'beast' :-)

Stu

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Thanks for the further comments folks  :smiley:

The EQ6 does look small compared to the scope but it's the biggest and heaviest EQ mount I've owned. The Meade tripod was designed to take the massive LXD750 EQ mount that held their 6" and 7" ED refractors back in the late 1980's. It is absolutely rock solid in every respect but it's made in the USA so has imperial threads and the EQ6 has metric of course, which is why I had to have a custom adapter plate made to mate the two together. Pete Larkin made the plate for me and did a great job  :smiley:

I managed to get a decent session with the scope last night. Setup time was around 20 minutes allowing for some care in assembly and placing a 7 foot 35 lbs tube on a set of tube rings 6 feet in the air  :shocked:

The scope takes 90-120 mins to fully cool.

I'll do a longer write up at some point but the images of Mars and double stars were excellent with 300x quite possible on the former. There is still some eyepiece end vibration but the damping time is around 3 seconds which I think is as good as I'm going to get with any mount that is remotely portable for this scope.

It's quite a feeling having that long tube poking up into the heavens as you peer into the thin end of it. Thank goodness for the EQ6 drives though, they do make the thing feasible and did a good job of tracking even though my polar alignment was somewhat cursory !

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Might be worth looking into Losmandy fittings for it John. I have similar, although not quite as extreme challenges getting the Vixen into its mounting but it does feel easier with the Losmandy. The plate I have is nice and long, and you just hook the bottom flange in then gently 'tip' the scope in and tighten, I suspect much easier and more secure than standard vixen dovetails.

I can take a few more pics to show it it that's useful.

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Cheers,

Stu

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Great description :-), it's certainly an impressive looking scope!

It's almost getting to the stage of giving better views by being above the thickest part of the atmosphere :p

Stu

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Might be worth looking into Losmandy fittings for it John. I have similar, although not quite as extreme challenges getting the Vixen into its mounting but it does feel easier with the Losmandy. The plate I have is nice and long, and you just hook the bottom flange in then gently 'tip' the scope in and tighten, I suspect much easier and more secure than standard vixen dovetails.

Cheers,

Stu

Thanks for the suggestion Stu. A Losmandy clamp / DT bar is something that I would consider however, as far as I can see the movement is in the mount axis rather than any flex in the DT bar. The Istar DT bar is Vixen / Skywatcher fitting but massively machined out of CNC as at the tube rings. 

I want to see if I can eliminate the mount axis as far as possible as a source of the tube movement before moving to Losmandy fittings.

I'm certainly not ruling out a move that way in due course though.

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Very impressive John! I could use a big tripod like that myself!

I got an extention pillar from FLO to lift my AZEQ6 Gt, and hence the Istar f10 higher off the ground. I ran into two problems that I need to sort. Firstly, the pillar turns when I push the tube manually - either the mass of the mount and tube together means the thread won't hold to the large screw at the base of the pillar (where the screw in the tripod fits into it) - I have to keep tightening it. Maybe the pillar base is threaded, but its not a satisfactory arrangement, as I keep losing alignment. The second problem I have is that the mount is now so high its a real problem getting the tube mounted on it (i'm a lot shorter than you are!) - I'm afraid I'll put my back out or drop the tube! I have a third problem - the eyepiece end is now too high for me when I observe near the horizon! Some sort of box or steps is needed (I guess Newt and big dob users are used to this!).

How do you propose to test and if needed rectify the mount axis flex you refer to?

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Great set up John. I had a good look over a 6" Istar refractor at PSP2012 and they sure are a serious piece of kit. Have you ever considered having a pier in your garden ? I would always have the worry of such a long scope toppling in the wind even on such a sturdy looking tripod as the Meade. I'm sure along with giving some piece of mind it would also add to speeding up your setup times.

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