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Carl Zeiss Jena Flektogon 2,8/35 aperture setting
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PostPosted: Sun Jan 20, 2019 4:03 pm    Post subject: Carl Zeiss Jena Flektogon 2,8/35 aperture setting Reply with quote

Fellow lens restorers,

I am currently cleaning a Carl Zeiss Jena Flektogon 2,8 35 (serial number in the 470xxxx range).

I noticed that at f/2.8 the aperture blades do not entirely retract. At the f/2.8 setting the aperture opening is 12.5 mm, at f/16 it is approx. 2 mm. That seems to make sense for the given focal length.

But I could set the slotted ring which drives the aperture blades off by one slot. This would make the blades entirely retract at f/2.8. Obviously, this also changes the smallest aperture opening: It would measure approx. 6 mm.

Does anyone have a known good Flektogon 2,8 35 at hand and can verify if the aperture blades do or do not retract entirely?

Thank you!

Dirk


PostPosted: Sat Jan 26, 2019 6:16 pm    Post subject: Re: Carl Zeiss Jena Flektogon 2,8/35 aperture setting Reply with quote

Once I started reassembling the lens the solution became obvious: The diameter of the lens right in front of the diaphragm is about 12.5mm. The proper setting for 2.8 hence is the "not fully retracted" position. Further opening the diaphragm would not allow any additional light to pass through.

fdlenses wrote:
At the f/2.8 setting the aperture opening is 12.5 mm, at f/16 it is approx. 2 mm. That seems to make sense for the given focal length.


Coincidence. And not necessarily true for other lenses. While reading about this topic I understood that it's not the real aperture opening diameter but the "entrance pupil" diameter (the view of the aperture opening through the lens elements in front of it).


PostPosted: Tue Jan 29, 2019 2:33 am    Post subject: Reply with quote

Thanks for clearing things up, as my flek it's got the same "issue" ,besides , i got the clickless lens (surely used for video be4) and would like to put the right "ball" into the diafragm as i am not used to the clickless for fotography. Wonder if that would be easy to find it ,even from another lens i've got for parts.