Carl Zeiss Jena DDR MC Sonnar 180mm/2.8 resistance to flare

miran · Joined: 01 Aug 2012 Posts: 1364 Location: Slovenia

So I have this lens I've posted about before (it's the newest MC version, P6 mount, says Carl Zeiss Jena DDR on the front with MC painted in red). I fixed it up so it now works but I'm not really convinced about its performance. I've seen claims that these lenses are supposed to be sharp wide open. Mine is maybe sharp enough at f/2.8 but there's a lot of ghosting (if that's the proper term) and also quite a lot of purple fringing so I'd say it's almost unacceptable wide open. Closing it down to just f/4 makes a world of difference and between f/5.6 and f/11 it's incredibly sharp (if I get the focus and everything else right).

But what I'm actually worried about is its resistance to flare. From what I've seen my copy is virtually useless in most situations, at least on an APS-C digital sensor (NEX-5) which is what I'm testing it on so far. As soon as there's any kind of light source (or even just a modestly large bright surface) anywhere near the frame, wide open there are huge flares that take over almost the entire frame and reduce contrast very much. And closed down these flares take the shape of large blobs and streaks across the frame, usually going through the center of the frame. Even when used indoors with no light source other than a window behind my back I get a noticable blob at the center of the frame. And if I shoot the other way, so that my object is backlit by that window, I can't even see what I'm shooting as the entire frame gets filled by a huge blob/streak.

So I'm wondering if this is normal for this lens and you just have to be extremely careful with positioning and framing or is there something wrong with my copy? To me it looks perfect, very clean, no scratches or anything, just a few tiny specks of dust here and there. When I was repairing it, I only took out the rear element to get to the aperture mechanism, so I can't have made any damage. It just seems to me the lens has huge amounts of internal reflections it can't deal with.

Any ideas, any recomendations? I'll post some sample images later if needed, I don't have any at hand right now.

miran · Joined: 01 Aug 2012 Posts: 1364 Location: Slovenia

Here are some boring samples.

First two are outside (actually from my window), sun behind my back, just a little bit of bright sky visible a long way out of frame. First shot at f/4, second at f/22. The blob in the first image is so big and diffused that it can't be seen, it just reduces contrast a little bit, but lets say it's acceptable. In the second image the flare is much more visible, in the center it's very distracting and it actually covers most of the frame, only the extreme left and right sides are ok.

Second example inside, window behind my back, white wall for background. First shot at f/2.8, second at f/22. Same story as the first except less severe. Loss of contrast in the center of the frame is actually visible already from around f/4 of f/5.6 (I tested all apertures, showing here only 2).

What I'm asking really is just whether this is normal for this lens or not? I've never seen any lens do so badly before. Neutral

themoleman342 · Expire: 2013-01-24

The only thing I can think of is that at f22 you're getting extreme diffraction and it's resulting in an odd sort flare/contrast-loss effect.

peterqd · Expire: 2014-01-04

This isn't going to be much help, sorry. I once had a Jupiter-21M with a similar problem - the flare became more pronounced as the aperture size was reduced. My conclusion was that it was due to internal reflections, probably due to lacking some of the black masking paint round the edges of the elements, but as the screwheads had all been broken I couldn't dismantle the lens to check.

You might try experimenting with a hood of some sort. I tried a rolled-up sheet of matt black card, but to get any decent pictures the hood needed to be 200mm long! The lens still sits unwanted on my top shelf.

With and without the hood at f22:

miran · Joined: 01 Aug 2012 Posts: 1364 Location: Slovenia

Thanks. Yes, this comes from internal reflections. The supplied (huge) hood is always on and doesn't help one bit. It helps if I use my hands to protect the lens more but that can only go so far. The odd thing is that it gets worse as I stop down, but it's visible already at f/4 and f/5.6. I don't see what diffraction has to do with it. I posted examples at f/22 just because the problem is more visible than at f/8 but I can post that too if needed.

aoleg · Joined: 22 Feb 2008 Posts: 1387 Location: Berlin, DE

I think I know exactly what the problem is: blackening of internal metal parts of the rear of the lens (or maybe the adapter). You are right in that you're seeing internal reflections; their shape and location make me think they are exactly the same type I had with one of my lenses.

Try putting black velvet inside your P6 adapter (to cover the entire inner tube) to stop these reflections. I am about 90% sure this will help. It helped me for sure; see the following two pictures. One is before modification, the second one was shot after I put some black foam around the insides of the rear of the lens (and adapter).

miran · Joined: 01 Aug 2012 Posts: 1364 Location: Slovenia

Thanks. That was my thinking exactly! Because I'm looking through this lens mounted on my 6x6 Kiev and I can only see normal flare when the sun or a strong light is in or near the frame, not what I see on my NEX with an adapter between camera and lens. I'll do some more testing and report back. I'll know for sure when I finish a roll of film with this lens. Smile

Farside · Expire: 2013-12-27

I have an old lemon - a Marep 200 (an importer's name), which exhibits the kind of flare you'd see in a distress flare factory on a distressing day.

If it wasn't for the flare it wouldn't actually be a bad lens. On looking at it, someone's had it apart, possibly to attempt a fix or maybe to fix some other fault and perhaps the elements' edge blacking got damaged. The T-mount and other metalwork internally show no bright surfaces.

miran · Joined: 01 Aug 2012 Posts: 1364 Location: Slovenia

I finally managed to make some more tests. It is indeed the adapter's fault! Nothing wrong with the lens as far as I can tell. The problem is this lens is for the P6 mount and I was first trying it out on a Sony NEX. Huge difference in registration distance which means the adapter is very thick. Actually I use two adapters: P6 -> A-mount -> E-mount. This adds a lot of length to the whole setup and there are a lot of reflections in the adapters. Now I don't know if this is a simple fact of life or just my particular adapters are bad. I only use cheap chinese ones, I don't know if a good expensive adapter is actually better.

The solution is simple. I folded a piece of thick black paper and inserted it inside the adapter. Immediate result! Still wasn't perfect, so I lined the paper with a piece of black fabric that came off a pair of old torn pants. Works even better. Looking through the lens with the naked eye, I can still see some light is reflected from the fabric, so I may have to look for something better but even so the difference is huge, even if it's still not perfect.

Here are some test shots for comparison. Four different scenes, left without, right with a paper/cloth inside the adapter. Aperture is f/11. In the first three the difference is subtle (although still quite obvious), but the last one (indoors, close to mfd and bright window in the background) needs no words:

Conclusion: if you have a lens with what looks like internal reflections, large flares and very low contrast, first check if it isn't actually your adapter. Especially on mirrorless systems where adapters can be quite thick. Smile