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oag and focus?


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in the sale section this is available, and im close ot buying it but i dont knwo if il need a low profiel one to achieive focus with my 200p and 400d? sorry if copying the picture breaks the rules but a pic is kindve needed to show the size of it.

also it has a slight chip in the prism on the end edge, the seller says they hvnt noticed any problems guiding, do you think this will be an issue? its going cheapsih compared to some brand new ones so i am temted but woul dlike some thoughts?? am planning to use this with a qhy5 when i get one.

thanks very much,



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I am not sure the Celestron radial OAG will work with your telescope. The OAG has a SCT female thread and is designed to attach to SCTs and similar telescopes with visual backs. Something you will need to consider when choosing an OAG is how much free inwards focuser travel you have available when the camera is in focus on a star before adding an OAG. If there is less than the overall length of the OAG free you will not be able to get the camera to focus with the OAG attached without modifying the telescope or using a low profile focuser. The TS low profile OAG for example, only adds about 9mm to the optical path.


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hmm now that is very annoying lol. i cnt afford that much money! maybe im better off getting the qhy5 and a cheap finderscope for guide for now then? I wouldnt bother with the qhy5 except for the fact that it contains a guider, which i would have to buy seperately otherwise for ~ 60 quid. hmm

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Ok there is what to do in order to work out if you can fit an OAG.

Focus your DSLR on your newt and measure the free space that you have in the focuser. Ie how much travel you have left in the focuser before you reach the minimum stop.

The OAG will have to fit in this space with all adapters required to make it fit.

The chances are you will only have about 10 - 30 mm travel to play with.

You need to check the attachments as well. How will the DSLR attach to the OAG and how the OAG will fit to the focuser.

Most OAGs have a 2 inch nose cone to slide into the focuser so this isn't normally a problem unless it has a SCT attachment as in this case.

But you will have to check the dslr side.

My 2 pennies, the TS OAG that I have will probably be the only decent one that will work for you. You can get an EOS attachment to the OAG and the OAG has a 2 inch nosepiece and the overall width of the TS OAG is about 9 - 10mm

Hope this helps.

I personally would recommend you go for a QHY5 and a finder / finderscope attachment from modernastronomy and start there. OAG's are good, but believe me, you need to know all this stuff before you start messing around with expensive bits of kit.

Get the basics of mount / scope and guiding sorted first for a few months before you even go near OAG's. You can always keep eye out of 2nd hand TSOAG and then sell the finderscope.

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Thanks Catanonia. I've still got lots to learn indeed! Many friendly people here are helping me tho :) I've found a gpusb guider for sale for 50, so I'm tempted to buy that and use it with my neximage (same as spc900 right, so shld be ok to get started with i assume ?) all il need then is a cheap finderscope. I have an old set of 12x50 bins that im sure can be modded into a finderscope alternative?

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