Wednesday, April 22, 2009

Optical Path Length Measurement

It's cloudy, so what to do? Previously, I've sent an email to Sibert Optics to ask for the optical path length of my Black Night, however, I didn't get any response, and I guess my email was probably trapped by the spam filter. So, why not measure it myself?

I pulled out my Borg 45ED II:-

I found that I can reach focus without a diagonal... so, it's time to remove the binoviewer and to use the eyepiece alone:-

I found that I've to use two extension tubes with a total length of 11cm and I also have to extend the drawtube on my Borg by around 1cm more. Therefore, the optical path length of the Black Night binoviewer should be around 12cm...

So, if I want to use the binoviewer without corrector with my Orion 100ED, I should then cut it by around 12cm.

After this experiment, I pulled out my Canon 10x30 IS for a quick comparison. The binoviewer Borg yields around 16x (with two 20mm Tele Vue Plossls). The view from the Canon is much brighter, and the 3-dimensional feeling is also stronger. Anyway, there is really not much a reason to use a binoviewer with a 45mm scope.


Harry replied and it's 12cm officially.

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