Sonnar's aperture shape

[regit]

I've been pondering on this now and then ... does anyone knows the logic behind the "star" shaped aperture/iris on a Sonnar between f4-8?

[darkkavenger]

It reminds me of the weird aperture that Jupiter-8M gets at certain apertures, unlike the traditional 50/2 Jupiter "Sonnar copy" design

[furcafe]

That's a historical question perhaps best directed toward the folks @ the ZICG (http://groups.yahoo.com/group/ZICG/), but it's certainly the main difference I see between the original, pre-WWII, Sonnars (& the post-WWII E. German Jena Sonnars) & the post-WWII W. German Oberkochen Sonnars.

[VinceC]

I always assumed it was a way for the designers to show off how many aperature blades they used.

Are the Oberkochen Sonnars the ones without stars?

[furcafe]

The Oberkochen Sonnars are the ones that make the star shape (actually more like a table saw blade shape) w/their aperture blades below f/1.5. The Jena Sonnars, pre & post WWII, all maintain a circular opening. I always assumed it was a way for the designers to show off how many aperature blades they used.

Are the Oberkochen Sonnars the ones without stars?

[JoeFriday]

does anyone have an example of the bokeh it produces? I have one of those funky lenses, but apparently I never shoot it at that aperture

[Mazurka]

I've been pondering on this now and then ... does anyone knows the logic behind the "star" shaped aperture/iris on a Sonnar between f4-8?

Probably the same logic employed by Leitz.

[regit]

Thank you all for the inputs and pointers :) I'll drop a note to ZICG and see what they come up with.

[JoeFriday]

here's what we're talking about, for those who haven't seen one

[Mike Kovacs]

If you look closely, you'll note two pairs of 12 aperture blades - haven't completely diassembled one yet but it must be a chinese puzzle to reassemble.

The prewar lenses have the roundest apertures. 50/1.5 has 14 blades, 85/4 has 20 blades.

[VinceC]

>>does anyone have an example of the bokeh it produces? I have one of those funky lenses, but apparently I never shoot it at that aperture<<

The bokeh is quite nice. But the flare -- well, that's another story. The lens is actually very well behaved, and I have quite a few sucessful photos shooting into the sun. But sometimes ... stars.

Here's an example of flare. Nikon S2, Sonnar, Kodachrome. Spain in 1989, either Madrid or Zaragosa.

[Mike Kovacs]

I keep a ventilated lens shade permanently affixed to my 50mm Sonnars. You can't have that large, exposed, front element unprotected from stray light.

Here's a sample, shot at f/2 on a 50/1.5 postwar Sonnar. It has flare, but that's the sun above his head. Bokeh looks good to my eye.

[VinceC]

I've never been a fan of lens hoods on rangefinder lenses ... the smallness of the camera is important to me. For the Sonnar, and for my Nikkor that has very similar characteristics, I compromised and started using a small collapsible rubber hood. The filter maker B+W has a very nice 43mm skylight filter with a built-in lens hood, and I use a 40.5-43mm step-up ring when putting it on the Sonnar. Since I started using it, my problems with flare have been reduced significantly (flare and lens reflections are still a problem when shooting into the sun or a bright light source).

Beniliam -- Thanks for confirming it was Madrid. The trip was a long time ago and this picture is from my box of seconds -- flawed or duplicate images. I really enjoyed the trip -- spent a couple of weeks in '89 driving through the central and northeast part of the country -- from Toledo to Madrid to Zaragoza to Pamplona -- eating lots of paella and learning the joys of tapas.

[Mike Kovacs]

I've never been a fan of lens hoods on rangefinder lenses

You can't have your cake and eat it too. A shot with higher contrast and lower flare is worth more to me. Even moreso with my uncoated lenses.

We'll just have to agree to disagree on that point.