binocular eyepieces

I am sure this is a silly question, but I will ask anyway. Can the primary objective (50 mm) of a pair of bino's be made into any serviceable 2" EP? I know that even if it does work its not going to be great, but if it would be decent it would be worth the effort. I like to play around with silly projects so its just eating up "fiddle" time. I have a pair of Celestron Bino's I dropped in the parking lot after a birding hike and I fractured the prism, so other than looking at birds in the yard, they are shot.

Dave, you said it yourself... "There's no downhill side to the learning curve." Hence, there are no silly questions, so long as they're sincere.

A typical 50mm binocular objective has a ~200mm focal length. I'm guessing you don't have a 20-inch f/40 Schiefspiegler, right?

Even paired up to make a Symmetrical/Dialsight/Plossl-type eyepiece, the effective focal length would be around 100mm.

To bring the effective focal length down to a more practical range, one or more "stronger" elements (shorter focal lengths) would need to be employed.

Cheers & best wishes.
-Dan

Dave budlong said:

I am sure this is a silly question, but I will ask anyway. Can the primary objective (50 mm) of a pair of bino's be made into any serviceable 2" EP? I know that even if it does work its not going to be great, but if it would be decent it would be worth the effort. I like to play around with silly projects so its just eating up "fiddle" time. I have a pair of Celestron Bino's I dropped in the parking lot after a birding hike and I fractured the prism, so other than looking at birds in the yard, they are shot.

Hi Dave,

Great question ! Maybe some interesting possibilities here. As Dan already mentioned, the FL of a symmetrical eyepiece using the objectives would be fairly long. Although you can measure this distance with the moons image, or sun if you are brave. If you use a 2" 2X barlow, that would cut the FL down to 50mm or so, making it somewhat more usable. Placing the barlow in front of a 2" diagonal or using a spacer would get you about 3X, so now we are down to 33mm or so. As Dan also mentioned, your ep wall diameter will most likely limit the apperant FOV. But you could easily do some experiments to see what works for you.

Another possibility is using the two objectives as an image erector. If the combined lenses are spaced at some distance from the primary image plane, the lenses will "relay" the image, but invert it also. If an eyepiece looks at this new relayed focal plane, it will see an upright correct image. Different spacings will allow you to get magnification or compression of the original image. To get 1:1 relay, I think you need to space the combined lense 2X the new focal length.