Back Focus for ST-8300M

Discussion in 'STF Series CCD Cameras' started by Mark Connolly, Jan 28, 2015.

  1. Mark Connolly

    Mark Connolly Standard User

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    I am using a ST-8300M with a .8 reducer on a Stellarvue SV80ed. I need 55mm back focus. Am I correct in reading that the ST 8300M has 17.5mm back focus?
    Thanks
    Mark
     
  2. Tim Puckett

    Tim Puckett Guest

  3. poldip

    poldip Standard User

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    Hello, I would like to refresh this question, just to be sure (I am also to design spacer for very sensitive reducer), because ST-8300 is not explicitly listed in the focus table.
    The distance of ST-8300M is identical as in STF-8300M.
    Right?

    Regards,
    Pawel.
     
  4. Tim Puckett

    Tim Puckett Guest

    Attached Files:

  5. poldip

    poldip Standard User

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    Tim,
    Thank you!

    One more question, if you don't mind.
    See please a photo of my camera. I guess it has the threaded adapter plate in front of FW5, loaded with Baader filters (glass thickness 3mm). (there is also a dust cap and 5mm T2 extender).
    So in my case the total backfocus is: 34.4 + 3.7 = 38.1 mm. Therefore for reducer that requires 55mm I need a spacer equal to 55-38.1=16.9mm.

    Regards,
    Pawel.
     

    Attached Files:

  6. EricC

    EricC Cyanogen Customer

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    Jan 31, 2015
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    Tim, I asked someone at SBIG about the 17.5 mm back focus in the .pdf file versus the 16.5 mm in the .gif file, and he said one was optical back focus and one was mechanical (?) back focus. If I recall correctly, the glass in front of the chip changed the back focus by 1 mm. Does that sound right?
     
  7. Tim Puckett

    Tim Puckett Guest

  8. EricC

    EricC Cyanogen Customer

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    Tim, thanks. The table shows 16.5 mm for the STF-8300 camera only and no filters.
    In the attached picture, that would be the distance from the left-most aqua colored line ( on the left side of what I call the "lip" on the front of the camera) to the right-most horizontal aqua line, which shows where the sensor logically is. So if I drew a line on the camera where the right aqua horizontal line is, I could measure from there to wherever the back focus starts on my scope? For example, my C11 SCT has a back focus of 161 mm, measured from the back of the scope. I could then measure 161 mm from there to the line I drew on the camera, and I'd be set, correct?

    [Update: I can't seem to upload the picture. It's a 763K .jpg file that shows my STF-8300 camera with back focus measurements. The web page says it uploaded but when I click the "Post Reply" button the attachment isn't there.
    The "lip" I refer to is on the front of the camera and sticks out about 3 mm. I assume the 16.5 mm camera-only back focus includes the 3 mm lip, so the back focus from the flat part of the front would be 13.5 mm, if I understand correctly.]
     
    Last edited: Jul 9, 2015
  9. Tim Puckett

    Tim Puckett Guest

    The backfocus is from the imaging surface to the front face of the camera.
    Email the pic to my email address so we can make sure of your configuration.
     
  10. EricC

    EricC Cyanogen Customer

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    Jan 31, 2015
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    The filter wheel web page (https://www.sbig.com/products/filter-wheels/fw8-8300/) says: "adds only 20mm backfocus (Total backfocus for STF-8300 with CFW5-8300 is 38mm)" but the backfocus table for "Camera + FW" implies 18.9 mm backfocus for the filter wheel not 20, and 35.4 for the camera and FW, not 38.
    I assume the filter wheel web page is wrong (and will be updated??) and the backfocus table is correct?

    I'm going to buy a custom adapter for $250 and want to make sure it's the correct length.
    The adapter will screw into the field flattener on my TEC 140 on one end and screw into the T-Thread on the OAG threaded adapter plate on the other.
    With this adapter, how would I rotate the camera?
     
    Last edited: Jul 29, 2015
  11. Tim Puckett

    Tim Puckett Guest

  12. Tim Puckett

    Tim Puckett Guest

    If you adapter is threaded on both sides it won't allow rotation.
    Where the threads tighten up will be the angle.
    You might need a different part.

    You can send me a private email or call me and I can try to help you with your specific setup.
     

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