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Ho Pei Jiun
12-Jan-2005, 09:49
Dear Sirs/Mdms,

1) What is the meaning of 'focus at infinity" ? How do we set a 35mm f2 lens to focus at infinity ?

2) Do you have any theory notes with schematic illustrations how the large format lense focus and calcuations of parameters like focal distance, depth of view, etc ?

3) Do you have any theory notes with schematic illustrations how the normal 35mm f2 lense focus and calcuations of parameters like focal distance, depth of view, etc ?

Appreciate if you can kindly advise me on the above issues. Hope to hear from you soon.

Sincerely,
Ho Pei Jiun

Ernest Purdum
12-Jan-2005, 10:22
It doesn't make any difference what the focal length, or the aperture, is, any lens is focused at infinity when the image of a very distant object is sharp.

Ralph Barker
12-Jan-2005, 10:49
As Ernest noted, focus with any photographic lens is simply a matter of moving the lens elements in relation to the surface it is focused on. With small-format camera lenses, that is accomplished by mounting the lens elements in a barrel with a helical focusing gear, while on view cameras the bellows substitutes for the lens barrel and the standards are moved.

You can find many of the related theories explained in the documentation for Robert Wheeler's "Photographer's vade mecum" program: http://www.bobwheeler.com/photo/Software/HP48DOC.pdf (http://www.bobwheeler.com/photo/Software/HP48DOC.pdf)

Depth of field is nicely explained in this article linked from the main page of this site: http://www.largeformatphotography.info/articles/IntroToDoF.pdf (http://www.largeformatphotography.info/articles/IntroToDoF.pdf)

You might also find David Jacobsen's Lens Tutorial helpful: http://www.photo.net/photo/optics/lensTutorial.html (http://www.photo.net/photo/optics/lensTutorial.html)

Arne Croell
12-Jan-2005, 10:51
You might want to check David Jacobsons lens tutorial at:

http://www.photo.net/photo/optics/lensTutorial.html (http://www.photo.net/photo/optics/lensTutorial.html)