35 EL Stopped Down...

When I stop down my EL to f16 the opening is not circular. It's almost in the shape of an eye. Why is this so? Are there advantages and disadvantages to this?

All Minox 35 cameras are like that ! My Minox GT-E diaphram also has <> shape when stop down.

As a matter of fact, two leave diaphram is quite common in P&S and APS.

Two piece diamond shape diaphram is also called 'cat-eye diaphram'. It was

invented by N. Norton in 1855.

<p> Minox 35mm camera has separate shutter and aperture diaphram.

<p> Many P&S cameras have cat-eye diaphram double as shutter. The cat-eye diaphram/shutter of this type of camera is usually closed.

When the shutter release is triggered, the electronic control of the camera opens up the cat-eye diaphram and then stop at the set aperture for duration of the shutter, for example, if the electronic sensor of the camera indicates a diaphram of f8 and 1/125 sec, then the cat-eye diaphram will stay at f8 for 1/125 sec, and then close down.

To get a near circle aperture, the minimum number of diaphram blades

is 7, and the blades must be computer designed to take certain

curvature, otherwise it requires 10 blades to make a good circle.

<p> Most 35MM SLR lenses,( including Leica and Zeiss lenses ) use 6

blades diaphram or 5 blades diaphram.

<p> Six blade diaphram forms a hexagonal aperture, 5 blades diaphram

a pentagon----in short, it is one blade per side.

<p> Cat eye diaphram uses only two blades, yet provides 4 sides.

<p> From a pentagon shape diaphram to a diamond shape diaphram, only

reduces 1 side, but the number of blades is cut down from 5 to only

2, great space saving for compact camera.

<p> How much difference from pentagon to diamond ? 20% difference

<p> The difference from 5 blades to 2 is 250%. Cat eye diaphram is very efficient, great for compact cameras.