diffraction vs aperture vs wavelength

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

Remember that discussion from many moons ago, here and/or on 
PhotoForum, about the relation wavelenght vs diffraction vs aperture, 
with diffraction being twice as bad at 800nm as at 400nm? 
The below articles more or less back this up IMO....

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
FROM: "Christopher M. Perez" <chrisper@xxxxxxxxxxx>
SUBJECT: Re: light diffraction and small appertures
DATE: Tue, 03 Nov 1998 16:40:21 -0800
ORGANIZATION: VND
NEWSGROUPS: rec.photo.equipment.large-format

Andre Calciu wrote:

> i was just wondering about light diffraction and small appertures.
> where does diffraction start to take its toll?

Use the following as a rough guide for on-axis resolution limits:

f-stop        theoretical max.
f8            200 lpmm
f11           150 lppm
f16           100 lppm
f22           75 lppm

Remember that the best current 6:1 contrast ratio scene rendered to fine
grained film will return around 120 l/mm.  So you can see that up to
f/16 film may set the limit of resolution IFF a lens' aerial resolution
is better than 120 l/mm.  Around f/16 diffraction can limit on-film
resolution.


> how does this varies with the format?

It doesn't.  It may vary between lens designs, figuring, alignment, and
mounting.  But not between formats.


> does the film speed/grain have anything to do with how diffraction
> affects it at the same apperture?

Just keep the 120 l/mm resolution limit in mind for fine grained films.
'Faster' films will resolve less.

I understand this doesn't go into great detail, but I hope it helps get
one started in the right direction.


- Chris

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FROM: kirkfry@xxxxxxx
SUBJECT: Re: light diffraction and small appertures
DATE: Wed, 04 Nov 1998 05:13:17 GMT
ORGANIZATION: Deja News - The Leader in Internet Discussion
NEWSGROUPS: rec.photo.equipment.large-format

In article <363FA04E.D1AC522A@xxxxxxxxx>,
  a.calciu@xxxxxxx wrote:
> i was just wondering about light diffraction and small appertures.
>
> where does diffraction start to take its toll?
>
> how does this varies with the format?
>
> does the film speed/grain have anything to do with how diffraction
> affects it at the same apperture?
>
> i love to hear answers from experience but also from theory as my
> knowledge of physics is slim and i enjoy learning more. i love this
> forum and thank the knowledgeable people who contribute.
>
> andre
>
> p.s. please email me a copy of your replies
>
This has been hashed pretty well before, formulas and all.  Check it
out on www.dejanews.com.  Lots of variables, such as enlargement, color of
light and such. The short answer is f32-f45 for 4X5 and f64-f90 for 8X10
because of less enlargement (you get more diffraction but you enlarge it less)
are the practical limits.   If you shoot resolution targets and read the
negatives with a microscope, you can can start to see the effects at f32.
Kirk

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--                 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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