Re: Konica IR ...!st time, hyperfocal focusing, and Stigmata

[Ben Kreunen <ben@xxxxxxxxxxxxxxxxxxxxxxx>]

At 04:05 PM 3/21/00 -0700, you wrote:
>OK OK, I'm too lazy to go lug out my textbook so I'll just ask this
>question:  I have heard the sharpest aperture on a lens is 2 stops down from
>smallest, i.e. an F32 lens is sharpest at F16.  You are saying that
>diffraction is worse at smaller apertures/higher F numbers?  And with
>infrared film this problem is accentuated?  Thus, what aperture would be
>best for shooting infrared?  I always assumed that the smaller the aperture
>the greater the depth of field (which, as you say, is exactly what I was
>doing with the hyperfocal focussing) which would in turn give me a greater
>chance of having a sharper image throughout.  At some point there must be a
>tradeoff/crossover between the two--depth of field vs diffraction, no?

Yes.  But it's more a case of resolution vs diffraction which is why I 
suggested a test on a flat subject. Just because more of your scene appears 
to be in focus doesn't mean that it is sharper. You get distracted by the 
appearance of added depth of field to really see any changes in sharpness 
on the area where you have focused.

If you ever get a chance to look through a microscope, then play with it's 
apertures at high power and you will see the change from low resolution 
wide open to optimum sharpness and then degradation from 
diffraction.  Otherwise, try my test in my previous posting.

Cheers

Ben

=======================================================
Gallery and Photography Tips (including IR)
http://www.bigbenpublishing.com.au/gallery/photography/
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