NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2016 Jul 19, 13:44 -0700
Attached is a graph for determine the minutes of arc per pixel for pixel counts from 700 to 3700 on the 28mm Pentax prime wide angle as used on a Canon Rebel 1.5 frame DSLR body. The 22 sextant horizontal angle images used to creat the graph took about 40 minutes to capture. Image processing and graph construction took about 1.5 hours. Checking for repeatability shows a spread between 0 and 3.5' toward so there is a toward error bias in the graph. The spread is about right for the expected +/- 1.4' precision of the 28mm wide angle. So far I'm satisfied with the results and the 41° field of view.
Greg Rudzinski
From: Greg Rudzinski
Date: 2016 Jun 7, 15:38 -0700
A vintage 28 mm prime Super Takumar M42 mount wide angle lens is now being calibrated for measuring Sun altitudes. This will be the first complete calibration of a lens for CN purposes using a metal sextant as the fixed angle standard. A few double polarized test images have been captured through the horizon mirror with excellent result using the Sun. The better plan is to use an offshore oil platform (4 nm away) for horizontal imaging every 2° through 40° of the 28mm practical field of view. The base multiplier is going to be .68' per pixel. This spells the end of the CN road for the Canon Rebel EOS Xti 10 MP digital camera body. The next evolution going forward will be a full frame 20+MP Canon (expensive but affordable used) which will increase the field of view to a very respectable 60° using the same 28 mm Super Takumar wide angle lens.
Greg Rudzinski
Attached File:
