Apperture in Pentacon 500 mm

Eugen Mezei · Joined: 17 May 2008 Posts: 265

I just got a Pentacon Prakticar 500/5,6 MC.
When I look from the frontside into it, the blades of the iris are still covering part of the lens when at maximum apperture. Is this normal? I've expected the baldes dissapear completly at 5,6.
On the other hand I don't see them, when looking from behind.
Can somebody please verify on his copy?

bernhardas · Expire: 2017-05-23

Edited

Oldhand · Posted: Wed Jan 01, 2014 9:19 pm Post subject:

I don't have the 500mm version, but do have a 300mm f4 Pentacon
The aperture blades on mine are near the front of the lens and can still be seen in the fully open position.
They can't go anywhere else as they need the thickness of their rim mechanism in order to operate.
I think you will find that this is quite normal.
OH

Lloydy · Expire: 2022-01-01

I've got a Meyer Optik Gorlitz 'Orestegor' 200 / 4 -which might be loosely related? I have a similar problem with the Orestegor, the wide aperture should be f4, and indeed the blades open all the way and a wide open aperture is there - but the ring shows f5.6. If I stop down with the ring to f22 then the blades are what I guess would be about f16.
When I bought the lens there was a bit of oil on the blades which I didn't bother about, and the aperture problem was a nuisance but it didn't stop me using the lens. Until the oil on the blades dislodged two of the blades, which I have managed to get back in without damage, I've also washed the blades.

My theory is, the previous owner of this lens had a load of blades jump out and also managed to get them back into the mechanism that moves the blades - but one slot out, which is why the ring doesn't correspond to the actual aperture. Maybe your lens has suffered a similar fate?