Backfocus and Field Flattener Sanity Check

Discussion in 'STF Series CCD Cameras' started by PeteFleurant, Apr 8, 2019.

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  1. PeteFleurant

    PeteFleurant Standard User

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    Hi,
    Please check this out and see if there is a problem.

    I need to spec the length of a "custom ring" between a field flattener and my FW8/STF-8300

    I (now) have a SkyWatcher 120mm ED Esprit Refractor that requires 75mm backfocus from field flattener to the CCD sensor.

    My sensor is a STD-8300 with FW8 w/o adaptor; the filters are 2mm thick (Baader 36mm).

    The backfocus chart I have from Diffraction Limited gives 34.7mm

    So the "custom ring" I will spec for PreciseParts.com should have an effective length of (75 - 34.7) = 40.3mm .

    Make sense?

    Thanks and clear skies!
     
    PeteFleurant, Apr 8, 2019
    #1
  2. Colin Haig

    Colin Haig Staff Member

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    Hi Pete - was good to see you at NEAF !
    You have calculated that correctly, assuming you don't have an adapter plate to have a different thread size on the top of the FW. If you do, I would plan for 3-4mm, shortening that 40.3 to say 37.5mm.
     
    Colin Haig, Apr 9, 2019
    #2
  3. PeteFleurant

    PeteFleurant Standard User

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    Colin,
    The picture of the FW8-8300 on the Diffraction Limited website (http://diffractionlimited.com/product/fw8-8300/) displays the FW8 with that 3.7mm adapter plate, correct?
    (I got he 3.7mm from the backfocus table "trjeaded adapter plate adds)

    Thanks!
     
    PeteFleurant, Apr 9, 2019
    #3
  4. Colin Haig

    Colin Haig Staff Member

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    Correct.
     
    Colin Haig, Apr 9, 2019
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