AO-8 before focal reducer to gain backfocus

Discussion in 'Guiding and Adaptive Optics - StarChaser and AO' started by Andrew Broadhurst, Apr 6, 2019.

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  1. Andrew Broadhurst

    Andrew Broadhurst Standard User

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    Hi - I am considering the following to gain some back focus as I need 105mm from FR (Celestron f6.3 in Agos adapter tube) :-
    STC Meade 14” LX200R / Pyxis 3” rotator / TCF-S focuser / AO-8 / FR / MOAG / CFW10 filter wheel / ST10XME camera.

    Please offer me some guidance folks as the adaptors needed are a bit expensive...
    Many thanks
    Andrew
    (Australia)
     
    Andrew Broadhurst, Apr 6, 2019
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  2. Andrew Broadhurst

    Andrew Broadhurst Standard User

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    Hi - I have a SCT (Meade LX200R 14”) and have purchased a Celestron focal reducer f6.3 in a short Agos adapter tube. Question - I need 105 mm back focus from the FR to the ST10XME chip so can I mount the my AO-8 in front of the FR in the following optical train:-
    SCT/ Pyxis 3” rotator / TCF-S focuser / AO-8/ FR/MOAG (with OAG guide camera) / CFW10 / ST10XME ???
    Assistance very much appreciated as the PreciseParts and Optec adapters are expensive and I don’t want to go down the wrong track with this one.
    Thanks
    Andrew
    (Australia)
     
    Andrew Broadhurst, Apr 8, 2019
    #2
  3. Colin Haig

    Colin Haig Staff Member

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    Hi Andrew,
    The Celestron f/6.3 reducers have around 105mm of backfocus with a 12" when attached in the normal position. I'm not sure about a 14, but its probably close.
    By putting it's optics into the Agos, normally the idea is that will be inside the TCF-S draw tube and you get some savings.

    The AO-8 needs 48mm.
    Then by having the FR, not sure how much that takes with the Agos and how close in it moves the available back focus.
    The MOAG takes about 50mm - this is a LOT - half your available back focus past the FR if it were normal.
    The CFW-10 is about 21mm + adapter plates.
    The ST10XME is about 19mm.
    I think it's going to be tight.

    So we have after the FR:
    50 + 21 + 19 = 90mm ASSUMING no plates, adapters, etc.
    If the FR still behaves the same, with 105mm, you have a total of 15mm to work with.
    If we add in any kind of adapters etc, you will run out of room.

    I suggest you ditch the MOAG and find a thinner OAG.

    This is one of those "test it and see" kind of situations.
     
    Colin Haig, Apr 9, 2019
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  4. Doug

    Doug Staff Member

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    Merged the duplicate threads.
     
    Doug, Apr 9, 2019
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  5. Andrew Broadhurst

    Andrew Broadhurst Standard User

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    Many thanks Colin and Doug. Yes I did the back focus calc myself and know its close. I suppose the question is will the AO-8 actually work in front of the FR in terms of stablising the image? I don't know as I have this gear and want some sort of guidance before I buy adapters etc....Preciseparts and OTEC talk about minimal back focus loss with the adaptors. The FR in the AGOS adaptor does slide right into the TCF-S focuser but as you say the AO-8 and MOAG take up a large chunk of back focus.
    Please ponder ...........

    Cheers
    Andrew
     
    Andrew Broadhurst, Apr 9, 2019
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  6. Colin Haig

    Colin Haig Staff Member

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    Pondered.
    I think (and @Doug feel free to jump in) -
    The AO-8 deflects the light that (goes through the FR) and hits the guide and main sensors in this new config.
    MaxIm has to be calibrated with the AO-8 in the new config.
    So it is as if you just have a new telescope and different pixel sizes.
     
    Colin Haig, Apr 9, 2019
    #6
  7. Doug

    Doug Staff Member

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    Correct. As long as you can reach focus, you will merely have to recalibrate the AO.
     
    Doug, Apr 9, 2019
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  8. Andrew Broadhurst

    Andrew Broadhurst Standard User

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    Thanks Colin and Doug !
     
    Andrew Broadhurst, Apr 11, 2019
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