building a lens

[Harold_2098]

Does anyone know what makes a lens able to handle a certain f stop? And how do you figure out what size opening is needed for an f-stop? Is there a formula for caluculating it? Edmonds optics(.com) sells good quality optics ($20 for a 250mm lens!) and leaf irises and I have a shutter. I would enjoy tinkering around with making my own lens but am a little short on the technical end. Can anyone fill in the blanks or suggest a book that might?

[Phil Brammer]

F stop is the ratio between the focal length of the lens to the diameter of the apeture. For example, a lens with a focal length of 200mm with an apeture of 20mm has an f stop (f ratio) of f10 (200/20=10). All the best with your experiments and let me know how you go!! Im all for home built stuff.

[Dave Willison]

Harold:

Track down a copy of Rudolph Kingslake's book "The History of the Photographic Lens." The first couple of chapters deal with simple lens designs used by 19th century photographers. The earliest lenses were meniscus type lenses, modified telescope lenses, or achromats with two elements in a single group. Kingslake provides diagrams of these lenses and the diagrams will give you some fertile ground for your initial experiments. Also, take a look at the following site which displays basic lens designs for many common lenses (tessar, planar, triplet, etc.):

http://www.linos-photonics.com/knowhow/lensdesi/lsframe.htm

For everything you ever wanted to know about optics, take a look at Optics Notes located at http://www.OpticsNotes.Com/. You may also benefit from the old Edmunds Scientific publication "Popular Optics," still avilable from Edmunds Scientific. The book contains all kinds of information on optical math, lens design, and several projects such as a drawing projector and a camera obscura. If you are really serious, you might want to consider lens design software. Do a web search and look for appications like OSLO.

I would also suggest the following surplus sites. Although Edmunds is a good source, you can pick up many used lens elements for much less.

http://www.surplusshed.com/index.html http://www.sciplus.com/ http://www.apogeeinc.com/optics.html http://www.aaaim.com/cgi-local/shop991/shop.pl/SID=48325726912/page=OP TS.htm

I hope this helps and good luck!

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[Harold_2098]

Thanks!