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Old 03-07-2016, 02:11 PM
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Shiraz (Ray)
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Shiraz is offline
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,820
the distance from the old focal plane to the new one will be about 4x the fl of the lens, so if you use say a 5mm GSO plossl, you would move the focal plane out about 20mm. ie a cheap 5mm Plossl should do the job. However, there may be issues with getting spacing right (eg, can you get the lens close to the CCD), so you may need to go for a bit longer focal length - a 9mm Plossl would move the focal plane out by about 36mm and that may also be practical.

the key thing for getting the position right is to find out where the focal plane is now. If you get a small bit of baking paper and move it in and out of the OAG tube, you will be able to see by eye where the focal plane is if you image a daylight scene. You should then put the 5mm Plossl at about 10mm further out and you should get a transferred image another 10mm out (again you should be able to see the image using baking paper).

Can you get someone to turn down the barrel on an eyepiece? anyone with a small lathe could do it - you need not protect the thread.

What camera will you be using for guiding and how far back from the front of the camera/nosepiece is the ccd? If you use a long nosepiece, you might need to fit the Plossl within it.

it will involve a bit of messing around, but if it could possibly save you hundreds and a bit of time, it could be worth persevering

Edit, it may also be possible to swap your guide camera for one that fits down into the AOG tube, if that is the issue - what guide camera are you using?

Last edited by Shiraz; 03-07-2016 at 02:41 PM.
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