building a lens

[harold]

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:

 

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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.):

 

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

 

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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.

 

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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.

 

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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

 

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I hope this helps and good luck!

 

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....................................

[harold1]

Thanks!