aperature number vs f number

guinness2 wrote:

Very interesting, thanks for the excursion into different world.

I suppose the eyepiece is represented by the rear lens glass on camera lens ?

Maybe someone more knowledgeable can elaborate since I'm no optician nor optical designer, but I suspect not in most cases. Here's why I think that...

A telescope's "objective" (i.e., its primary optic, whether a mirror or lens) delivers an image at the focal plane which is at its focal length. An eyepiece is simply a magnifier through which a larger view of that "prime-focus" image is seen. It is -- or should be -- a high quality magnifier for sure, but still just a magnifier.

Comparing a camera lens to a telescope isn't entirely apples-to-apples. I suspect a camera lens delivers a prime-focus, i.e., non-magnified, image. For example, when a 100mm lens' focal plane is coincident with the sensor (or film), the image is in focus at 100mm.

Do the last few rear elements in a lens effectively comprise an eyepiece? Dunno for sure, but I would be surprised if they do in any but the odd case. For example, maybe a lens designed to deliver a long effective focal length in a short physical package? Imagine a lens that's natively 80mm but the last elements magnify the image by 3x, so you have effectively a 240mm lens. I've not heard of that, but maybe it's possible. There are folded optic lenses, but that's a different design.

So there's my non-committal answer!