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|6th December 2017, 10:38 AM||#31|
Join Date: Jun 2002
Location: USA, MN
Businesses exist to make money, they don't make money by making a product to fix an issue that affects very few people.
Look at the bottom of this page:
You find a well-known formula there: 1/F = 1/f1 + 1/f2 - a/f1f2
If you buy two lenses and separate them by a distance "a", you can create many focal lengths. If you buy two lenses and mount them to a helical focusing mechanism that varies the distance between them, you can create a variable focus lens. You have to be smart about what you choose for f1, f2 and a.
I have a feeling you will want perhaps a 0.25 diopter lens, with a focal length of 4meters (4000mm) You will probably want one of the small lenses to have a positive focus, and the other to have a negative focus.
lets try a +50mm and a -50mm - now for some math!
a = 2500/4000 = 0.625mm
I did that in my head, can you believe that?
Lets say you wanted a 0.5diopter lens, with a focal length of 2000mm with the same lenses - the separation distance would then be a=2500/2000, or 1.25mm.
I have a question for you though: Is it weird that I use the capacitance meter setting on my DMM to check LED's?
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley
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