Strange Lens Problem

[jrsmith]

Twice this year I have encountered old Hasselblad Zeiss ‘C’ lenses (silver ones, a 60mm and a 50mm) with serious problems in the glass. Has anyone else come across this?

 

The problem appears as a network or series of very fine, straight lines, which seem to have spread across the glass element. They only show up when a strong light is shone against them from the rear, or when a light is shone across the glass at a very steep angle. Along with the lines there is also a cloudy, milky appearance. I have seen this twice now, as I say, and both times it has been in the middle of a front or rear group, not on the element at front or rear of the cell which could be cleaned. As it is in the middle of a closed cell it is hard to understand how this has happened. Is this some sort of fungus, or if not, what is it?

 

Both times the lens has had to be retired from service.

 

John

[bob_sunley]

<p>Could be fungus, or possibly stress cracks in the cement from a drop or hit. Or both.</p>

[leicaglow]

<p>I have never seen this in my lenses, but it could be fungus, or just haze. Usually fungus doesn't look so even in pattern. You might compare it to photos on a google search: <a href="https://www.google.com/search?q=what+does+lens+fungus+look+like+hasselblad&hl=en&biw=1024&bih=515&prmd=imvnsfd&source=lnms&tbm=isch&ei=u3GzTp9PxN2IArOm_Uk&sa=X&oi=mode_link&ct=mode&cd=2&ved=0CAsQ_AUoAQ#hl=en&tbm=isch&sa=1&q=what+does+lens+fungus+look+like&pbx=1&oq=what+does+lens+fungus+look+like&aq=f&aqi=g-S1&aql=1&gs_sm=e&gs_upl=139295l139295l0l139737l1l1l0l0l0l0l399l399l3-1l1l0&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=ebc83987b1f653&biw=1024&bih=515">click</a></p>

[q.g._de_bakker]

Can you show pictures of the stuff in your lens, John?

[jrsmith]

<p>Michael</p>

<p>Thanks for the link. The problem I have seen in my lenses does not look like any of those illustrations, unfortunately. And QG, well I could get a photo of this but it would take ages to set up because the glass has to be lit in a specific fashion to see it clearly.</p>

<p>If you can imagine that you have the circle which is the lens element, and then draw a series of random, very thin, white straight lines across the disc, completely covering it from one side to the other. The lines criss-cross and tend to be thicker and closer at the rim of the lens element, as you would expect. The lines are only visible when strongly backlit or side-lit.</p>

<p>At present I have prepared for the worst and assumed that this is fungus, and the lenses have been quarantined away from my other glass.</p>

<p>John</p>

[q.g._de_bakker]

I have a pair of glasses with anti reflection coating that has gone crazy (as in: crazed), showing a pattern (also when viewed in the 'right light') that looks similar to what you describe.<br>But those lines are not white and there is no overall milky appearance. And that crazed pattern is caused (i believe) by mechanical stress on the acrylic 'glasses', something you wouldn't get on rather rigid glass.<br>Still, since it's not likely that the glass itself started to erode and acquire a patina already, it must be something that's on the glass. Which is why the crazed coating sprung to mind. Could it be another, similar thing, like a crystalline deposite of some stuff that evaporated elsewhere? I don't know.<br>But another thing, besides a.r.-coatings, that is often found on the glass is indeed fungus. The pattern fungus creates is not predetermined, and could be like your description. The mily haze could be the deposit the fungus grows on (an oily film, most likely. A condensate/deposit of oil and grease evaporated elsewhere in the lens) gone milky by the 'metabolic action' of the fungus. The lines appearing to be white could also point towards fungal growth.

[rodeo_joe1]

<p>The only "fault" I've seen that results in parallel lines or striations appearing in a lens is an interference pattern caused by a slight wedging or curvature mismatch in a cemented pair. This doesn't seem to suddenly occur, but is a manufactured feature of the lens.</p>

<p>This, like John's description, is only visible under particular lighting conditions, but unlike the above description appears as coloured faintly red/blue alternate lines. They may also run across the lens or in concentric circles. I suppose if seen by a strong transmitted light they would appear as a pattern of dark and light banding, but I haven't managed to make them visible in that way myself.</p>

<p>Just out of curiosity, I really would like to see the effect you're talking about John.</p>