|
The back focus scale used in the TV docs has a zero point some 55mm from the top surface of the lens housing. The rear of the lens is 10mm below this surface.
So, the distance behind would be the actual measurement from the top surface of the lens housing minus 65mm.
""
For astro-imagers, the above chart indicates the magnification for each Powermate™ (2x, 2.5x, 4x & 5x) as a function of distance from the Powermate™ eyepiece holder top surface to the imaging surface (CCD or film). (Imaging through a DSLR with the Powermate™ T-Ring Adapter and camera T-Ring — without added extensions — brings the focus position to 0mm.)
""
|