STT-8300/FW8G back focus question...

Discussion in 'STT Series (obsolete)' started by Chris Anderson, Aug 11, 2017.

  1. Chris Anderson

    Chris Anderson Cyanogen Customer

    Joined:
    May 27, 2016
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    109
    Location:
    Lamasco, KY US
    Hello. I am going to change up my imaging rig to include (once again) a Takahashi QE 0.73x focal reducer. It has a critical metal back distance of 72.2mm. The STT manual states the back focus of the STT8300M+FW8G-STT filter wheel is 54.06mm. So, I will need an adapter extension tube to reach this critical focus:

    72.2mm - 54.06mm = 18.14mm + 1mm (for 3mm Astrodon filters) = 19.14mm

    My question is this. Does the aforementioned 54.06mm take into account the thickness of the CCD cover plate? Am I correct in assuming, based on the 3mm thickness of the Astrodon filters I employ, that I do in fact need to add 1mm additional length to my adapter? This is correct, yes? The extra 1mm will not affect luminance images? Said another way, am I adding too much extra? I had read in another posts where the 72.2mm was very important to achieve, but tossing in the filters has me worried and confused.

    Or am I over thinking this?

    Thanks! Chris
     
  2. Doug

    Doug Staff Member

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  3. Chris Anderson

    Chris Anderson Cyanogen Customer

    Joined:
    May 27, 2016
    Messages:
    109
    Location:
    Lamasco, KY US
    Doug:

    I am SO glad I posted up here! So, with a bolt-on Precise Parts adapter, I am good at 52.5mm into my equation....

    Chris
     
    Last edited: Aug 14, 2017

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