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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12565
Loc: Cumberland, R I , USA42N71.4W
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Re: Pentax 20x60 PCF WP II (Prisms undersized)
06/11/08 01:07 PM
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One of our members here in the CN binocular forum sent me his Pentax PCF WPII 20x60s so i could test it. It arrived today and I happened to be home from work, so I measured aperture.
Checking exit pupil at the full aperture I get a 3mm exit pupil. This would lead most people to believe it is a full 60mm aperture. However, this measuremeent by itself is insufficient to tell anything about the actual magnifiaction and aperture.
Using a scale at the objective end and using a loupe to read clear aperture, I get a reading of 57mm.
Placing a 50.5mm aperture mask over the objective end and remeasuring exit puipil, if magnification were truly 20x then the exit pupil would now remeasure 2.53mm. With the 50.5mm mask, I get an exit pupil of 2.65mm. With a 50.5mm aperture and a 2.65mm exit pupil, magnification must be 50.5/2.65 = 19.06x
Now getting back to my first measurement of exit pupil, if aperture is 57mm and if magnification is 19.06x, then I should see a full exit pupil reading of 57/19.06 = 2.99mm. My full aperture exit pupil reading is measured 3mm. This checks.
These measurements and readings check between the two methods.
The Pentax PCF WPII 20x60 actually measures 19x57.
These are maximums. I rechecked all measurements and got slightly lower in the second set of data.
Thanks Stan, for helping me resolve a controversy. Real measurements trump speculation every time.
edz
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