Back focus distance help

Discussion in 'STT Series' started by Paul Kirk, Apr 4, 2020.

  1. Paul Kirk

    Paul Kirk Standard User

    Joined:
    Oct 31, 2015
    Messages:
    4
    Hi All,
    I purchased an SBIG STT8300m and a FW8G-STT a few years back from Ian King Imaging in the U.K.

    It's a really nice camera - works really well and is reliable. I have one small problem which I am looking to correct - not a camera problem I feel, but one to do with the threaded adapters which attach the camera to the Celestron C11. The problem is this, in the top left corner of my images the stars are not round because the camera is slightly tilted. So I thought I would purchase an adjuster like this:

    https://www.altairastro.com/altair-m48-camera-tilt-adjuster-212-p.asp

    But I have two questions:
    One is that the device adds 10 or 11 mm to the image train. Will I still be able to focus my camera if I install this device?
    The current setup is C11 with 0.8x reducer, FW8G and then the camera.

    the other question which I need to refer to the supplier of the adjuster is whether the adjuster can support the weight of the camera. So I looked on the Diffraction Ltd website at the spec for the camera and FW. The camera weight is 1.7 pounds, but the site states the FW weight is 2.2 oz which is not correct.

    So if the answer to the question about backfocus is positive, could someone let me know the weight of the FW please?

    (Edit - I have just found the weight of the FW in the documentation I had with it 39.7 oz/ 1150g, so just need an answer to the backfocus question - thanks)

    thanks to all for help with this.
    Paul Kirk
     
    Last edited: Apr 4, 2020
  2. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    4,280
  3. Paul Kirk

    Paul Kirk Standard User

    Joined:
    Oct 31, 2015
    Messages:
    4
    thanks for this Colin. Is the chip in the STT8300m adjustable to align it with the focal plane using something like CCD Inspector?
    best wishes
    Paul
     
  4. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    4,280
    No, this is done at the factory. Usually they are within 1/1000".
    Because the optical axis and mechanical axis of the telescope/focuser/rotator/filterwheel etc all the way to the chip aren't always perfect, people will install 1 or 2 shim washers between the mounting bolt on the coupling between the filter wheel nosepiece plate and coupling to the draw tube.
    A shim washer is a tiny thing. Here are some examples:
    https://www.mcmaster.com/steel-shim-washers/
    Stainless Steel is better for outdoor use.
     

Share This Page