CARL ZEISS JENA MC FLECTOGON 20mm 2.8

Dear Friends, I have a very good Carl Zeiss Jena MC Flectogon 20mm 2.8 lens in very good condition. The aperture blades seem to be stuck wide open. The starry sky picture made with this lens looked like a bunch of doughnuts wide open. I am trying to solve two issues here: better focusing at infinity (obviously) and also would be glad to find experts in the UK, preferably not far from Oxford who could have this lens repaired on a budget. Aperture blades seems to be the only issue here. I am connecting it to my Nikon D500 via an adapter that has a glass element (for obvious reasons) and definitely would need to try this lens on a mirrorless camera. Would be grateful for all your thoughts on aperture blades repair and the infinity focus. Thank you.

The aperture blades seem to be stuck wide open.

Quite common with old CZ lenses. Oil migrates to the iris blades and causes 'stiction'.

 

The iris mechanism needs a thorough clean and degrease, which probably won't be cheap.

The starry sky picture made with this lens looked like a bunch of doughnuts wide open.

That's a result of using a lensed adapter. Fit the lens to a camera body that doesn't need a lens in the adapter and most, or all, of that aberration will go away.

Thank you. Do you know anyone who does that kind of CLA for the Carl Zeiss Jena lenses?

If you're in the UK, you might try contacting Ed Trzoska of Euro Photographic Services:

 

Euro Photographic Services

I don't know this particular lens but it's sometimes possible to free up a stuck aperture by unscrewing the rear lens group giving access to the blades. If there is oil on them, try repeated swabbing with a small amount of lighter fluid on a cotton bud followed by a dry cotton bud. Stuck apertures aren't always caused by oil on the blades, there can be a gummed up or siezed mechanism, or even a tiny spot of dry oil or dirt which can be dislodged by working the blades.

 

You can sometimes see enough of a sticking focus helix with the rear group off too, to get a little oil into the grooves and free it up.

I don't recommend experiences on this lens. They are not cheap (anymore) and complicated construction.

 

A few german repair shops do service this lens, mostly ones specialised in repairing GDR gear. It is not very expensive. But I don't know where the OP is from.

Edited October 16, 2020 by eugen_mezei

BTW, this lens is a true classic, and a real pioneer:

 

here is the Modern Photography take on one of them:

 

 

Modern Photography 1963-08

It's definitely worth spending the service cost

I owned this lens years ago and agree it is a true classic, worth repairing if you plan to use it often, if not, sell it disclosing its condition, I'm sure you'll find a buyer in short order who will put it to good use.

Good and classic, agreed.

With a unique rendering? Nah!

 

A 20mm f/3.5 Ai Nikkor is its equal, except the Nikkor has more contrast and better flare resistance. And a tad more aperture - probably equal to half a stop taking transmission into account

 

If I was in the market for a used 20mm manual-focus lens, my 200 quid would be going in the direction of a Nikkor, not a Jena lens with possibly stuck iris blades.

Edited November 17, 2020 by rodeo_joe|1