SC-3 focus adjustment: Spacer plate between SC-3 and FW8S-STXL?

Discussion in 'Guiding and Adaptive Optics - StarChaser and AO' started by Evert Cooper, Sep 11, 2021.

  1. Evert Cooper

    Evert Cooper Standard User

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    My problem is that focusing the SC-3 puts its focal plane up against its inner stop with its blur spot still out of focus, i.e., its focusing range seems inadequate. My understanding is that focusing the SC-3 matches the adjustable focal plane to pick off mirror distance to the distance from pick off mirror to main camera focal plane. For my camera system, which is an STXL 6303 + FW8S (3mm filters) + SC-3 + AO-X, drawings show that the optical back focus distance from STXL 6303 focal plane to the top of the FW8S is 42.77 mm. Using a scale, I measure an additional distance of 12 mm from FW8S top to the SC-3 pick-off mirror midpoint, for a total of 54.8 mm. The SC-3 has a measured focal plane to pick-off mirror adjustment range of 57 to 87 mm. To match the available adjustment of the SC-3 I therefore need a spacer in the optical path to the STXL 6303 of 57-54.8=2.2 mm minimum. Preferably it would be better to have a little more adjustment range, say a 1/4 inch or 6.3 mm.

    Questions:
    1) Do my numbers make sense?
    2) Is this an item that I overlooked in assembling the camera system from you folks?
    3) Does SBIG have any of these spacer plates or do I have to machine and anodize them myself?


    I didn't see any similar question on the forum. Thank you for your help,

    Evert
     
  2. Doug

    Doug Staff Member

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  3. Evert Cooper

    Evert Cooper Standard User

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    Dear Doug, thank you for your quick reply. It is amazing how much info is available on this website if one knows that it exists and where to look. Let me work on figuring out the exact spacer thickness, using your 3D printed spacers. To whom do I give my dimension? You? or someone else?

    Again, thank you for your help,
    Evert
     
  4. Colin Haig

    Colin Haig Staff Member

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    Evert, Doug will help you out if you need something.
     
  5. Evert Cooper

    Evert Cooper Standard User

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    Doug, would you kindly make the spacer between the FW8S-STXL filter wheel and the SC-3 to be 3/4 inch thick. This will give me 7/16 contingency for measurement inaccuracy, to further adjust the pickoff mirror a little closer to the edge of the KAF-6303 chip, as well as some room for comfortable focusing.
    Please let me know if you have a better number.

    Thank you,
    Evert
     
  6. Doug

    Doug Staff Member

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    Okay, will do. It'll take a couple of days to fab it.

    Can you find suitable screws to mount it? They'll go straight through the spacer.
     
    Last edited: Sep 14, 2021
  7. Doug

    Doug Staff Member

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    Here's the adapter.

    IMG_2823.JPEG

    IMG_2824.JPEG

    You will need some longer screws... I'll leave that as an exercise for the reader.

    Please confirm that your shipping address has not changed. If it has please let me know ASAP.

    Doug
     
  8. Evert Cooper

    Evert Cooper Standard User

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    Doug, wow, that was fast work. You folks do stand behind your product! Attached is a list of available 6x32 SS screws from McMaster. Don't think that I will have any problems obtaining the screws. Same shipping address.

    Thank you very much,
    Evert
     

    Attached Files:

  9. Evert Cooper

    Evert Cooper Standard User

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    Got it. It arrived this morning. Looks beautiful.
    Thank you,

    Evert
     

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