MPCC coma corrector - getting 55mm back focus

[gerardsheldon]

I have a MPCC Mark III coma corrector (Baader) and a 294MC colour cooled.  I am trying to get a 55mm back focus. 

I don't know where 0mm on the coma corrector is relative to the focal plane.  By 0mm, I am referring to 0mm in the second photo with a camera where 55mm back focus is achieved with two extenders. 

If I ensure that there is 55mm to the camera in the first photo, is that correct? 

 In other words, do I just use the two extenders and connect the coma corrector, having removed the thin ring that comes with the coma corrector (see red arrow in first photo)?

  

 

[bottletopburly]

If you use the M48 fitting the backfocus becomes 57.5 mm +/- 1mm probably more 1mm rather than less  omit the two spacers use just the main cell 

Edited December 26, 2022 by bottletopburly

[gerardsheldon]

Thanks very much.  It was not that clear from the available information.