Asa Yam

[Shelley]

Hi Asa,

While at lunch with a bunch of Palma shooter buddies of mine, I asked this question. Does anyone know what the focal length of a 24X63mm Unertl spotting scope? The only answer I got was that I should ask you as you have an uncanny ability to ferret out all sorts of obscure information.

I bought the Unertl and it has fantastic optics but it was a bit underpowered for seeing bullet holes at 600 yards if there was any mirage at all. So I purchased a Celestron 12.5mm telescope eyepiece, took out the lenses from the new eyepiece and with my lathe made a new package to hold the 12.5mm lenses. It works great and judging from comparing with other scopes I believe the Unertl, with the new eyepiece, to be about 40X. I know that if I can find out what the actual focal length of the scope is, I can divide that by 12.5 and the answer will be the X power.

I tried e-mailing Unertl twice, asking for the focal length and explaining why I wanted to know, and they never even bothered to acknowledge my question.

Anyone else that may have the answer please help.

Thanks
Shelley

 

[Asa_Yam]

Shelly,

Strange you should ask - I Googled "Unertl spotting scope focal length" and got this:

http://www.benchrest.com/forums/showthread.php?t=19326

Post #8 there is a reply to you!

You divide the focal length of the telescope by the eyepiece diameter and that gives the magnification. My 90mm has a focal length of 1250mm divided by 40mm yeilds approx 32 power. Using the 26mm yeilds 48 power.

Actually, "diameter of the eyepiece" in the quote above should read "focal length of the eyepiece".,see http://www.celestron.com/c2/category.php?CatID=30 ) This is relatively easy to measure - remove the eyepiece, and shine a light through the ocular lens,i.e., the one you normally look through). Move the assembly up and down until you get a focussed point, then measure the distance from the ocular lens to that point of focus. You know the approximate magnification of the scope & eyepiece, so work backwards.

 

[Shelley]

Asa

I already know the focal length of the eyepiece,12.5mm). What I don't know is the focal length of the telescope or main part of the scope. It might could be measured except the light passes through a couple of prisms, inside the scope and that confuses the issue of measuring the distance.

Perhaps my little brain just isn't wrapping around the problem here. OOPs.... You've caused my brain to work a bit. If I use your method to determine the focal length of the Original eyepiece that yields 24X I can calculate the focal length of the scope and then calculate the power using the 12.5mm eyepiece. Thanks Asa!!!!!

The focal length that David Halbloom refers to in the BR.com thread is an entirely different scope than the Unertl that I'm concerned about.