Re: Diaphragm Stars and Printing

[ADavidhazy <ANDPPH@xxxxxxxxxxxxxxxxxx>]

> Andrew Davidhazy pointed out that "the anti-reflection coating is on
> the surfaces of the lenses and not on diaphragm or shutter blades".

> I don't think I was getting confused. I think this may differ from
> camera to camera since I had a Minolta SRT-101 where the manual
> referred to an anti-reflective coating on the iris blades in their
> Rokor lenses. It didn't seem to work though since I could get great
> stars at f22 :=) Of course this could just have been bog-standard
> anodising (?) given a marketing spin in 1960s Japan.

Agreed that having diaphragm blades that do not reflect light is a good thing
but normally anti-reflection coatings are thought of in terms of lens surfaces.
On the other hand, anti-reflection coatings on metal I do not think will have
much of an effect on what happens at diaphragm blade _edges_ which is where the
diffraction ocurrs. ... as substantiated by your experience.

> Presumably any coating that affected the edges of the iris diaphragm
> would also affect edge diffraction effects? Or am I too long away
> from high-school optics?

I am not sure I am putting this the right way but if this were the case we 
would not have diffraction limited lenses. It is precisely diffraction at lens
or diaphragm edges that limits the resolving power of lenses. Smaller apertures
result in less resolution.

cheers,

Andy
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