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Thread: Which Focuser to use to achieve prime focus for Astrophotography?

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    Default Which Focuser to use to achieve prime focus for Astrophotography?



    Hello! I was recently given a Newtonian type reflector telescope with a 6 inch mirror of really fine quality and some very expensive eyepieces. Now so far i'm a refractor kind of guy and this type of scope is all new to me but one thing i am sure of...I want to use it to take pictures!

    The OTA has a diameter of 7 inches, an outer radius of 23 1/8 and a length of 31 and 1/2 inches. It has a hole cut for the focuser already. The old 1 1/4 focuser is unusable so i removed it. The hole for it is about 2 inches in radius and has 2 sets of mounting holes for different patterns. My question is this. Which focuser would you recommend i get for this scope that will allow me to achieve prime focus using a DSLR?

    I see that Orion recommends an 8-12 inch OTA for it's Crayford style one. This is smaller than that. Will i have to move the mirror? Thanks for any help in this matter. I'm on a mission to get this baby up and viewing!
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    First step: point OTA at the moon, hold DSLR (without lens) up to the focuser hole, and back slowly away while looking through viewfinder. If you can reach sharp focus, that'll show you how much room you have to play with. Then see if you can find a short enough low profile focuser; otherwise, you may need to look at moving the mirror.
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    Default Re: Which Focuser to use to achieve prime focus for Astrophotography?

    I agree with Jerry, you need to figure out at what distance past the edge of the tube you achieve focus. Once you know this, ciphering the numbers is fairly easy. The "not quite as easy" part will be remounting the mirror if that is needed. Here is great calculator to help figure out the distances once you know the prime focus number. NEWTONIAN TELESCOPE DESIGN PLANNER (I.E. version)

    Hope this helps,
    JT
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    Default Re: Which Focuser to use to achieve prime focus for Astrophotography?

    Great advice you guys many thanks for the starting point. Time to get calculating! I do see Antares makes a low profile 2' 2 speed focuser and i found one for 165.00.
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    Default Re: Which Focuser to use to achieve prime focus for Astrophotography?

    Found an awesome deal on an Antares low profile focuser and though i still had to move the primary mirror up a bit it's so worth it! Love this thing. Thanks Thomas!
    The BOBSONIAN (1 of 1)-4.jpgThe BOBSONIAN (1 of 1)-5.jpg
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    Default Re: Which Focuser to use to achieve prime focus for Astrophotography?

    Hi Levy,

    I love it when a plan comes together. That looks awesome! Can't wait to see your images.

    Nicely done,
    JT
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    Default Re: Which Focuser to use to achieve prime focus for Astrophotography?

    I agree! Love this site and all the helpful people. Pictures soon!
    My eyes
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