Jupiter 3 mystery deepens!

[Duncan Ross]

I've had exposure problems with my Kiev-mount J3 and assumed the fault was play in the aperture ring. However a little experimentation reveals the play covers a fraction of a stop at about f5.6.

But the lens is underexposing by about 1.5 stops at f5.6.

Any idea what is happening?

 

[vicmortelmans]

I assume that the ring stops moving right at 1.5 and at 22? Did you also measure other apertures? How did you measure in fact? Put it on a camera with meter and compared to another camera?

On my m39-mount Jupiter 3 I notice that the ring movement is a bit wider than the provided scale. When I reassembled the lens, I just fixed the ring such that it is right on the 22 mark at the one end. Now it can be moved a bit further than where the 1.5 mark is. Of course, I could also have fixed the ring to stop right on the 1.5 mark, but then it would pass the 22 mark almost as much as the difference between 22 and 16... It's a psychological reassurance of correctness, because I have no means to measure the aperture correctness.

Anyway, when using small apertures, you should take into account an error of at least 1 stop on these lenses, I figure.

Groeten,

Vic

 

[Ash]

bigger vodka ration that day in the factory

 

[Duncan Ross]

Compare the opening to another 50, like a J8.
I doubt the lens is that far off.

What is the best way to compare the apertures? Should they look similar from the front or the back?

 

[Duncan Ross]

Compare to another 50, preferably another FSU 50. At 5.6 they should both look the same.
Hold them up to the light like binoculars. 🙂

Thanks Gman, I've had a look and this is a J3 and a Menopta both at f5.6.

 

[Ash]

ouch... looks like at least 2 stops difference!