On 2020-11-04, Martin Brown wrote:

On 03/11/2020 21:45, NY wrote:
"Martin Brown" wrote in message
...
For general use I use my reading glasses and long distance one stacked.
(much like the clock guy on the repair programme)

I'm intrigued how that works, optically. How would a high
positive-dioptre lens (reading glasses) close to a lower
positive-dioptre lens (distance glasses) increase the effective power of
the reading glasses to give greater magnification and/or allow you to
focus closer to the work? I've just tried it with my reading and
distance glasses (both with reading and with distance glasses closer to
my eyes) and it makes no difference to magnification or closeness of
focussing

It if they are used consecutively it should give a compound lens with an
approximate focal length fF/(f+F). Mine are 3 diopter and 1 diopter.

You are crudely mocking up a Ramsden eyepiece when you do this. It works
best if the glasses being stacked have about the same focal length.

http://hyperphysics.phy-astr.gsu.edu.../eyepiece.html

Interesting, thanks. Optics was one of my favourite parts of physics,
but I've forgotten most of it.


If the long distance glasses are anything less than 1 dioptre I doubt if
you would really notice the difference. A cheap pair of 2 diotre reading
glasses in combination with your own formula ought to be noticeable.

I'll have to watch The Repair Shop and see if I'm doing it correctly...

The clip on loupe is much preferable for very fine work.