Back to front refractor

[DeanWatson]

Here's the idle thoughts of an idle fellow... I was teaching my astronomy might class at the local college last night and I was talking about 'scope specs, how to calculate magnification and all that stuff.  Then a thought occurred to me while driving (or fatigue addled episode perhaps, I had worked a full day as well).  Lets say you have a refractor with a smallish aperture, say one of the evoguides with 50mm.  Now, (of course this is all hypothetical and a bit of nonsense), if you used an eyepiece with a large exit pupil, say, a two inch one with a long focal length (I haven't tried this with any of mine, as I say, just playing) given that an eyepiece is in focus where the focal length of objective and eyepiece meet (broadly), would it be sort of possible ( I didn't say desirable...) to use the objective as the eyepiece and vice versa given that in the final analysis optics is optics?

 

Have fun with that...!

[Clive]

Have you never looked through a refractor or binoculars backwards? It certainty seems that the laws of optics still work, or am I missing something?

[DeanWatson]

27 minutes ago, Clive said:

Have you never looked through a refractor or binoculars backwards? It certainty seems that the laws of optics still work, or am I missing something?

Oh absolutely, that was my point, I was just musing how well it would work astronomically.

[philjay]

Its all down to the figuring of the optics, focal length etc, not the diameters.