Lenses with shiny irises

[JohnBar]

Here's a little puzzle...

I have a Xenar 2.8/50 with a shiny iris. I mean really shiny and not through wear either.

Normally, irises are made of springy steel dark blue/grey. Not with this one, which has shiny steel iris.

This got me thinking about the behavior of the light when say the iris is closed down to F16 say.

Well the light that goes normally through the hole will be nice and sharp, but wait

the shiny iris will reflect back light like a mirror which will bounce off the elements internally and eventually that weakened light will go thorough the hole as well. This is the action of a reflex/mirror lens, how weird?

This weakened light may not be focused by the rear group and if looked at alone would maybe be a soft de-focused diffused image at lower intensity.

So the result would be the addition of the sharp image with the weakened diffused image superimposed.

With this Xenar I am seeing these effects and find them pleasing. A kind off soft over sharp look.



I wonder if you have an understanding of shiny irises, perhaps my understanding is incorrect?

I also wonder what would be the effect if the iris was a true mirror and would the resulting image be interesting or crap.

[guardian]

[fotografiasol]

Hi. I also notice this. Please, see the diference between an Helios with a near black iris (MC Helios-44M-7 from Valdai 1994) and one with a little shiny iris (the most frequent case, this is a MC Helios-44M-5 from Valdai 1992), the blades can be seen in the picture! Cheers.

[BurstMox]

Btw, I always wondered why some medium format soviet lenses (like Jupiter-36, Tair-33) have brillant almost gold colored aperture blades...

[JohnBar]

@fotografiasol

welcome to shiny iris club

[JohnBar]

@BurstMox

so have I

[ForenSeil]

Jupiter-12 has an very shiny iris aswell, can give funny effect when stopped down heavily
You can even see the oil from the blades on the pic

[Olivier]

[CuriousOne]

"Gold color" is anodized aluminum, without paint applied.

[Olivier]

Issue in my case is that there's an annoying round halo when stopping down.
I'm now wondering wether it's due to the shiny copper blades because the circle is not centered.
What could it be ? I don't know. A light linkage ?

The Mir-38B 3.5/65mm facing light, wide open :
#1


Same shot but stopped down :
#2

[Oldhand]

I have had this kind of thing happen to me before and I was truly puzzled. It didn't appear wide open but when stopped down it was even more pronounced than yours. A solution was simply a large lens hood.
Try it and see.
OH