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C11 GEM OTA on a CPC11 fork mount?


DrRobin
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Hi,

Does anyone know if it is possible to mount a C11 OTA designed for a GEM mount (it has one Losmandy dovetail fitted) on to a CPC11 fork mount?

The reason for asking is I want to look at mounting my C11 in to a small dome and the EQ6 it is presently on won't fit.

If I can't mount it on a CPC11 fork mount anyone know of anything similar that it will mount on?

TIA

Robin

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You will need to make an adapter. CPC mount doesn't use dovetails and it is not sold separately as mount only. I believe the only way to get a CPC11 mount is to buy it from someone who has de-forked his.

It may be easier to swap or sell your EQ6-C11 and then buy a CPC11.

Alternatively an Avalon M-Uno single arm fork mount is designed to carry a C11

http://www.iankingimaging.com/show_products.php?category=177

Edited by E621Keith
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Thanks Keith,

My C11 is actually a C11Edge, so I was considering buying a CPC11, removing the OTA and fit my C11Edge, just not sure if they share the same hole centres? A new one is a possibility, especially if I can sell the OTA to offset the cost, but a second hand one would be okay, I might even keep the OTA for planets. I am not sure the Avalon would fit, I think it will take up as much space as my EQ6.

Robin

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Unless you are doing DSO imaging, then is there any advantage of the Edge over the "standard" OTA? The only one that I can think of is perhaps a quicker cool-down due to the vents?

You can't be the CPC mount on it's own, so you'd be looking for one that someone has stripped the OTA from.

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It is for DSO imaging, there is no advantage of the Edge over the standard for anything else. I will look for a complete CPC11 once I know that it will fit and then swap the OTA over. I might end up with a C11 OTA, which I could sell on after attaching a dovetail.

That is unless I am lucky enough to find a CPC11 or Nexstar 11" fork mount on the second hand market.

Robin

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Sorry, Robin, I think I misunderstood this. You want to use a CPC11 Edge for deep sky? Surely the fork mount will need a wedge?

Chris

If so, surely then it'll take as much, if not more, space than the same OTA on an EQ6? And an EQ6 will be marginal for DSO imaging...my standard C11 is wobbly on my 6.

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Hi,

Yes I was expecting to use a wedge. Overall size/height is going to be about the same as my eq6, but a fork mount can keep the centre of rotation inside the OTA whereas an EQ mount has it on the centre of the mount. I still need to check but I don't think an eq6 and C11 is going to fit inside the obs I have in mind, but think the fork mounted C11 does.

I wouldn't say mine C11 on eq6 is wobbly, I do have it on a heavy pier and wind can be a bit of an issue, but 5 minute guided exposures are fine. Mounted in a obs I should be ok even with a bit of wind?

Robin

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I use mine on a wedge - it is the HD wedge, and you are right, without wind it is fine. I can manage 20 minutes without wind, but I don't have an obs. I find the main difficulty is accurate polar alignment, but a permanent setup would overcome that. To avoid vibration, focusing is best achieved electrically - I don't like the standard Celestron focuser and would like one day to change it for a rack and pinion type. Of course to reduce exposure time you could always use a hyperstar, but that rather defeats the object of having a long focal length scope for very small and faint stuff.

chris

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You might also want to check that there'll be enough clearance between the rear cell and the fork base to accommodate the imaging equipment that you're intending to use - with a fork mount there's the potential for your camera to crash into the fork base when the scope is pointed towards objects at higher declinations. Or will you just be using Hyperstar (saw it referenced in your signature)?

IMHO you should either try to see if your EQ6 will fit into your proposed dome or would it be possible to get a slightly bigger dome?

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Robin, here are some measurements you may find useful:

Height from base of wedge to base (centre) of CPC = 330mm

Max height of CPC from base of mount to top of tube = 950mm - i.e. total max height from pier/tripod = 1280mm

Clearance fro base of tube to mount = 190mm (I don't have a problem with clearance using an Atik 4000 and SX filter wheel)

Chris

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Thanks everyone.

Mike, Chris has probably answered the clearance question. Hyperstar is superb at wide field, but bypasses the Edge's correctors and it is longer focal length I was after really. I am checking with the dome supplier to see if an EQ6 and C11 will fit, or for that matter a CPC11 fork mount.

The house and gardens manager of my estate (my wife) has given permission for a small dome and I found a really nice automated one in the US (Robo-Dome), just big enough for a telescope and not much else. I like the idea of an automated dome, just set it up leave it to it and it will shut down at the end of a run. I will get a cloud/rain sensor and that shuts the dome in the event of cloud. Where it has permission to go, I am not sure a 2.2m dome will fit or get approval, so if my C11 won't fit inside I might have to have a re-think.

Chris, nice to know that an Atik4000 + wheel fits. I have been looking at the Atik 4000 mono and pretty much made my mind up until I saw the new cameras from Starlight Xpress, the model with the same chip looks interesting. The dimensions will also help.

Nice to know that a fork mounted C11 is reasonably stable. I doubt very much will be stable in wind, but inside an obs, it should help. A permanent set up not only reduces the set up and strip down time, but as you say helps with alignment. I currently use a pier, bolted on to a concrete base that I remove every time and store indoors. It goes back in the ground in nearly the same spot every time so polar and star alignment is never far out, just a quick check and adjustment and it is there.

Robin

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Chris,

Sorry forgot, I fitted a Baader Steeltrack to the rear of my C11 and made a Skysky USB motor focus for it. I use the main focus knob for coarse focus (keeping the camera distance optimum and then tweak with the USB focus on the Crayford. Sharpsky (http://www.sharpsky.net/) is ASCOM so integrates in to all of the software tools.

I made my Sharpsky unit, but I see there is a commercial version out now by the guy who designed the original. I think you can still DIY if you can make up a circuit.

Robin

Edited by DrRobin
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