Re: IR and pinhole

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

On 30 May 97 at 12:49, JoePaduano@xxxxxxx wrote:

> Bob, in all the years I have worked with infrared film, I have never found
> that a small aperture would cause a loss in picture quality with infrared
> film. In fact I have found just the opposite to be true, when I have shot
> with larger apertures, I have noticed a loss of picture quality. Kodak
> confirms this fact and recommends using the smallest possible aperture in
> their Applied Infrared  Photography book from a number of years ago. 

Both Guenter Spitzing's UV/IR bible and a Russian publication warn 
against it.
There is also the rule that pinhole optics work very well with UV,
as an alternative to unsuitable glass lenses (UV-reflective/opaque);
in contrast to IR, where diffraction is a major factor. 

Diffraction is linear related to wavelength, at 800nm it is twice as
bad as at 400nm, therefore one should not stop down as much.
There is an optimum aperture for every lens, beyond that aberrations 
& diffractions increase.
A discussion on the PhotoForum list ages ago only confused me 
further, as someone at RIT (I think) said that 'diffraction-limit' 
with perfect lenses did not apply to most photo lenses, where other 
abberations were involved, also increasing beyond a certain optimum 
aperture.
I know we are talking about a very small aperture with a pinhole, but
considering that it is an significant factor with pinholes, it
doesn't seem strange that with normal lenses small apertures are
also detrimental for image quality.

Helmut, does Guenter Spitzing mention this subject in his first
edition more extensively? His first edition contains much more
pages....


- -- 
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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