Thanks Anthony!
It all makes sense now. A while back I read that to test alignment of
the focussing screen, you should use a wide angle lens. I guess it
comes down to the same thing.
Frank.
On Mon, Aug 13, 2001 at 02:52:56PM +1000, Anthony Farr wrote:
> In answer I will quote myself from a previous unrelated thread.
>
> "Wide lenses ..... have very short depth of focus, ie the tolerance for
> focussing error at the focal plane. ..... the cone produced by the image
> forming light is very wide so that a very, very small change in lens
> extension will make the circle of confusion unacceptably large. OTOH a long
> lens has a narrow cone of image forming light, and will tolerate a quite
> large change in lens extension without exceeding the parameters of
> acceptable circles of confusion."
>
> This should clear up a very common misconception.
>
> Regards,
> Anthony Farr
--
Francis Tang, Postgraduate Research Student.
LFCS, Div. of Informatics, Uni. of Edinburgh, EH9 3JZ, UK.
Tel: +44 131 6505185. Fax: +44 131 6677209. Office: 1603, JCMB, KB.
Email: [EMAIL PROTECTED] WWW: http://www.dcs.ed.ac.uk/home/fhlt/
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