Baader Hyperion Zoom – thoughts from a newbie

[Don Pensack]

I did 3 timings of a star in the 24mm UFF and got a field diameter of 27.3mm +/-0.05mm (level of uncertainty caused by very slight fade out at the edge), for an eAFoV of 65.2°

You measure using a ruler, correct?  And in your case the uncertainty is from distance to the target and magnification error possibilities?

Interestingly, timings of stars also gave me 36.4mm +/- 0.05mm for the 30mm field diameter.

Yet, in daylight use, both eyepieces have visible rectilinear distortion in the form of pincushion.

Why the 24mm has a larger eAFoV than its measured AFoV is a mystery.  It should have barrel distortion.  

 

I did the same with all the UFF and got eAFoV approximately the figures claimed.  I wonder if the actual field diameters were ever measured at the factory.

[Louis D]

50 minutes ago, Don Pensack said:

You measure using a ruler, correct?  And in your case the uncertainty is from distance to the target and magnification error possibilities?

Yes, a ruler.  I did an analysis of photographed field versus known good field values from Televue and other online sources for eyepieces I own.  I arrived at a best fit coefficient to convert the photographed distance to the field stop value in millimeters.

Error can creep in whenever I setup again (I try to get the distance correct to with less than an inch over 35 feet or about 0.002% error).  A bigger error creeps in because I eyeball the distance which can allow me to see more than could be seen from the center by swiveling my eye and looking to the side.  As the image fades off to black for eyepieces with poorly defined field stops, where do you declare the actual field stop edge?  This is an even bigger issue with eyepieces having massive chromatic aberration at the edge.  Is the edge where all colors are present or where the last color is present?  Should field stop be defined as the edge visible from the center of the eye lens or is peeking in from the edge of the eye lens allowed?

If I had a 24mm Panoptic, I'd probably be able to get a much more accurate field stop number for the 24mm APM UFF using differential distances and the official FS value from TV.  However, it's tight eye relief precludes me from buying one.

I went back to my images and recalculated the 24mm APM UFF as a percentage of the 27mm Panoptic's 30.5mm field stop (TV specs) since I have images of both and arrived at 27.2mm for the APM.  Your 27.3mm value is probably right on the money.

Edited September 27, 2021 by Louis D