Gee where do you guys learn all these?? Or how do you manage to find the
time to delve into such esoterica.
Regards
Titoy
----- Original Message -----
From: John A. Lind <jlind@xxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Friday, July 20, 2001 5:32 AM
Subject: Re: [OM] Aperture Modification
> At 22:49 7/19/01, Paul Wallich wrote:
> >At 11:00 PM +0100 7/19/01, Chris Charlton wrote:
> >
> >>Just a question, after reading about Ansel Adams,
> >>"F64" club using very small apertures to gain the
> >>maximum depth of field and detail, does anyone think
> >>it would be possible or worthwhile modifying a cheap
> >>wide angle (eg Vivitar 28mm) to go down smaller than
> >>F22? Would there be any noticable increase in depth of
> >>field or detail captured?
> >
> >You would get more depth of field, but you would start
> >losing sharpness dues to diffraction. At f/64 a 28mm
> >lens would have an aperture of about 0.44mm. The general
> >formula for diffraction is that the first minimum (roughly
> >the width of the central spot) is at an angle of L/A, where
> >L is the wavelength of the light and A is the aperture. For
> >yellow light, L is 600 nanometers, and A is about 440,000
> >nanometers, so L/A = 1.36 milliradian. That means the smallest
> >spot you can image is in the neighborhood of 28 mm (the focal
> >length, i.e. the approximate distance the light travels from
> >the aperture) x 0.00136 x 2 (cuz the light spreads out on all
> >sides). That would give you a spot size of about 0.075 millimeter,
> >or a resolution of about 15 lpm. (I'm leaving out a bunch of
> >stuff here, I know, but it's close enough).
> >
> >So the answer is, you could do it, but it probably wouldn't be a
> >great idea.
> >
> >paul
> >
> >--
> >Paul Wallich pw@xxxxxxxxx
>
> A spot size of ~0.075mm is about 3x the circle of confusion maximum
> diameter (0.025mm) for 35mm small format. What's that mean? The max.
dia.
> CofC is as large as a spot can be on the *film* before it becomes
> discernable as a finite spot and not perceived as an infinitessimally
small
> point, by an average unaided human eye, at normal viewing distance, in a
> *print*. In other words, photos made using f/64 with a run-of-the-mill
> 28mm prime lens would be very, very soft (zero sharpness anywhere). This
> is the same reason pinhole photographs look severely soft-focused; the
> diffraction limiting Paul spoke of in his posting.
>
> -- John
>
>
> < This message was delivered via the Olympus Mailing List >
> < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|