Cameras and Lenses
Eyeglasses for birding
A dedicated pair of eyeglasses for birding is a good idea as it can solve quite a few problems.
Some requirements based on my experience:
- round if possible as they fog less with air gaps where you don't need the glass (well, plastic).
- close tight fit to the eyes (to minimize ER)
- high index to make the lens thinner to minimize ER (even though it generates more transverse CA at the edges). Makes more of a difference if you have a strong prescription. CR39 is optically a better choice (and cheaper too).
- strong frame that seats well on your nose so you can press on it without it digging into you or flexing or popping a lens. I find a rimless frame a bad choice both from comfort and the need to make the lenses thicker to carry the load (especially with CR39).
- with anti-reflective coating. You don't want to loose 4% just in front of the eyes now do you after obsessing over your bins transmission.
You can even use regular lined bifocals if you keep the line out of the ocular i.e. you place the line much lower than usual (aligned with the lower lid) but you have to be prepared to make some measurements to get the placement right (a digital camera and a ruler works well!). You need to explain to the eyeglasses maker what you are doing too.
The are quite a few internet optics companies that can turn out reasonable glasses at reasonable prices for single vision or bifocal use(but avoid progressive lenses unless you really want to learn about ophthalmic optics ... the fitting is critical).
I'm curious how others deal with wearing eyeglasses and using bins. Do you have a dedicated pair of glasses for use with bins?
Ophthalmic optics! A whole new field of optics to obsess about 
Well, yes, obsess. Is it the objective lens, or is it the eyepiece? At least we don't need those troublesome, high math requiring prisms.