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Upgrading the focuser on C8...


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Im thinking of upgrading the standard focuser on my C8 SCT, ive noticed that you can buy Crayford focusers for them.......my question is, it it a question of simply unscrewing the thread for the eyepiece and screwing in the upgraded focuser??? Ie the primary mirror doesn't move anymore, just the focuser, and im guessing you can blank of the old focus knob??? Any ideas??..........

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You can either upgrade the stock focuser or attach a crayford directly to the sct thread on back of tube. Yes, you will mainly focus with crayford after rough focusing with the stock focuser. Image shift will subside, plus no mirror flop. It will add a bit of weight to that side of tube if you go the crayford route. I would not seal off stock focuser as it is still easier to get a rough focus and if you ever just wanted to not install the crayford, you will still have something to focus with.

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I just took delivery of this: <a class='bbc_url' href='http://www.telescopehouse.com/acatalog/Revelation-Superfocus-2-inch-SCT-Rack-n-Pinion-Focuser.html'>http://www.telescopehouse.com/acatalog/Revelation-Superfocus-2-inch-SCT-Rack-n-Pinion-Focuser.html</a>, and it is very good for the money. I bought it for fine focus for imaging, and it simply screws to the SCT thread on the back of the scope (2"). :D

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I have both the Revelation SCT Crayford (on my PST mod) and the R&P (currently off my C9.25 whilst I motorise it).  They're both pretty good for the money and not much difference in cost between them.  Perhaps not quite as nice as, say, the Steeltrack, but they're much better than half as nice and they are half the price :D

If you fit a secondary focuser I'd leave the primary exactly as it is.  External SCT focusers don't tend to have a lot of travel (most are only 30mm I think) and you may well need the primary focuser to get close depending on what you're hanging off the back.

I chose the R&P for the SCT because I've no idea what kit I might end up using it with and the rack (especially combined with a motor drive) gives a bit more resistance to movement than just a lock screw on the crayford.

James

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I use a Moonlite on my C11, and IMHO, it transforms the 'scope. Trying to do planetary imaging with the standard focuser is nigh on impossible. you will need to leave the original focuser as-is as the mirror will still need to be racked in and out when you add barlows/diagonals/cameras.

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Moonlite on insulated C11

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Sorry for taking so long to reply to my post.......my internets been down for day or so.........think your information is great, poss gonna go for the rack and pinion type, and like you all say keep in place the original focus knob...........

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