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Re: [OM] Aperture Modification

Subject: Re: [OM] Aperture Modification
From: Chris Charlton <c_charlton@xxxxxxxxx>
Date: Fri, 20 Jul 2001 01:51:40 +0100 (BST)
 --- Paul Wallich <pw@xxxxxxxxx> 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


Whoooooshhhh..........

(That was the sound of that flying over my head at
high speed...)

Chris ;o)

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