SHINY APERTURE BLADES

[Rolleinut]

This is my first posting, hope I don't screw up.

I have often wondered why some lenses use hi gloss metal for apreture blade. It seems to me that would contribute to flare.

I have the following cameras with glossy blades:

Rollei 35 with a Tessar

Rollei 35SL SLR with a Xenon

Pentacon in a M42 mount.

I am surprised at the Zeiss and Schneider lenses.

Maybe it doesn't matter?

Rolleinut

[visualopsins]

Welcome Rolleinut!

I think internal reflection is called ghosting. Reflective aperture blades do contribute to ghosting imho.

There was an earlier post by another member asking how to blacken aperture blades. I don't know if there were any recommendations. Perhaps "gun blue" could be used? Whatever the method, the coloring should not scrape off; reflective scratches may cause more evident ghosts than a bright surface. The colored surface must be smooth for snappy aperture.

[scsambrook]

Rolleinut makes a good point - I suppose light coming into the lens could be reflected back onto an interior lens surface and cause flare or internal reflections ... but does it happen? Maybe it would be more of a problem if a lens had misting on any of its surfaces?

I can't say I've ever noticed such a problem. The 135 Pentacon has shiny blades and a wonderful reputation ... so does the 85/2 Jupiter. My Jupiter 135 has shiny blades - really shiny - but they don't seem to be a nuisance.

I think I read that DSLRs can get sensor reflections, but can't recall where.

Anyway, welcome on board, Rolleinut!

[no-X]

Maybe I'm missing some particular situation, but I can't imagine, how could glossy blades affect anything:

if the ray is "allowed" to pass the diaphragm, it won't be reflected

if the ray is blocked and reflected by the diaphragm and reflected back again by the nearest air/glass surface, it would be blocked (or reflected) by the diaphragm again





I can only imagine one exception - a double-gauss lens with very strongly curved lens surface covered by poor coating... such surface could reflect tiny amount of light on the camera sensor, but I think the difference in contrast would be indiscernible...

[aoleg]

[scsambrook]

For what it's worth ... in Miniature and Precision Cameras (Lipinski, 1956) there's mention of light being reflected internally within lens mounts and being scattered from uncoated surfaces causing loss of contrast on film. If that did indeed happen, I see no reason why shiny iris blades can't cause similar problems. Although I think it's more of a theoretical issue than a practical one with modern lenses. [edit: - with film]