Light seperation

[WootSK]

Hi, I have a small query to ask the pros here. I have just gotten a Schneider- Kreuznach 90mm F8 from Ebay. The Lens front cell has a light separation that looks like coating wear off. I am wondering the effect of it on image quality at F16 and above.

http://gallery.clubsnap.com/data/500/Light_seperation.JPG

I bid for the lens knowing the risk as the seller is honest and posted photo of the light separation. Item arrived as shown in the photo clearly.:)

[Brian Ellis]

I don't know whether it will have any effect on the image but I wouldn't want a lens that looked like that unless it came at a real bargain price and I could test it and return it if I was unhappy. However, I'm not a pro or a lens guru by a long shot, maybe someone here who's one or the other can give you more assurances than I can.

[WootSK]

After some intensive "googling", it seems like a lens elements separating issue and are common with old lens when the cement fails. I did heard of such issue before from one of my LF peer who commented on Rodenstock old lens. First time seeing it, but still would like some guru to clarify and maybe tell me about the effect of it on image quality at F16 and above. Thanks

[WootSK]

I don't know whether it will have any effect on the image but I wouldn't want a lens that looked like that unless it came at a real bargain price and I could test it and return it if I was unhappy. However, I'm not a pro or a lens guru by a long shot, maybe someone here who's one or the other can give you more assurances than I can.

Thanks for the reply. I gotten it at a petty good price. I don't think it is right to complain to the seller since he already highlighted the issue unless there are others issue which are not highlighted then I will consider returning. For now, I am just hoping for the best when I bring it out for a test run. Asking here first is just some form of mentally preparation for the worst.

[Steven Tribe]

Isn't the separation (or coating deterioration?) in the middle - rather than the edges?
Have you checked for Newton rings when viewing at an oblique reflective angle?

[E. von Hoegh]

I don't see separation, but I do see loss of paint.

[lenser]

I'm not a lens guru by any means, but I'll try a couple of thoughts.

First of all, don't just test at f16. You need to test at all f stop ranges because the optical performance may and will change according to how much of the edge light is organized and eliminated by the size of the iris opening. This is true of all lenses, not just this one.

Next, tape a full sheet of newspaper to a wall and make it as flat as possible. Make sure it is illuminated evenly from side to side and then set up your camera so that it is perfectly parallel to the paper. Make your test exposures of that newspaper at each f stop and label each with a post-it note in frame as to the f stop used. Doing this by available light (if the lighting is even) will be simpler and also give you a thumbnail test for shutter performance at the same time. Be sure you do an incident meter reading or a gray card if a reflected reading. Otherwise, you will be underexposed and that won't tell you anything about shutter performance.

Carefully focus for each exposure with a good loupe so you are certain of accurate focus technique. When the film is processed, examine each exposure under a loupe from corner to corner and in the center for sharpness of the type in all areas of the frame. This should reveal any problems in the overall lens focus performance whether or not it is caused by the separation.

From the image you show, it isn't possible to tell for certain whether this is limited to just the edge separation, or whether it extends inward. If it is limited to just the edges, I would think it unlikely to have a very great effect unless it begins to spread more toward the center or unless the separation was caused by impact which could have easily knocked other elements out of alignment.

By they way, I've got a handful of ancient brass lenses, some with a corona of edge crystalization of the balsam cement but which still give me awesome results. I've never even bothered to test them like this because I'm happy with the images I get.


Good luck.

Tim

[Steven Tribe]

I could see the loss of paint flakes on the ground glass edges (schneideritis) which gives the reflected optical morse code around the edges - but I could also see a central cloud which begins about 1/3rd of the way into the centre?

[Ari]

I'm no lens expert either, but just shoot with the lens and see what you get; follow Tim's suggestion to test it out, and then take it out for a real-world tryout.
My sharpest lens has a little separation and fungus, so you never know what you may get; odds are there will be no effect on your images.

[John Koehrer]

All the separation I've seen has been a very distinct yellow(ish) cast.
If you remove the front group can you see if either element has had the coating partially removed. You may need a glass to determine if it's on the surface or inside the lens.

[WootSK]

Thanks for all the answers. I guess end of day, the chance is still 50/50. I will bring it on a spin in the weekend and hopefully the result is good. Thanks alot for all the reply.

[eddie]

All the separation I've seen has been a very distinct yellow(ish) cast.


there are several other looks to separation. some are pinpoints, others are little hand shaped flower petal figures etc etc. i think gandolfi posted a image of his lens that has this kind of separation.

from the OP image of teh lens it looks like a coating issue to me. not separation.

[Ole Tjugen]

"Schneideritis" has no known effect except to make the selling price a little lower.

Slight edge separation may possibly have even less effect, except in the case of the original old Schneider Angulon f:6.8 lenses, where the inner elements in each cell were only held in place by the balsam.

If separation has a "very distinct yellow(ish) cast" it is likely to be caused by aged balsam, not more recent synthetic cement. "Rodenstockitis" (Rodenstock lenses of a certain age range seem especially prone to this) has no visible (or at least obvious) colour cast.

[WootSK]

"Schneideritis" has no known effect except to make the selling price a little lower.

Slight edge separation may possibly have even less effect, except in the case of the original old Schneider Angulon f:6.8 lenses, where the inner elements in each cell were only held in place by the balsam.

If separation has a "very distinct yellow(ish) cast" it is likely to be caused by aged balsam, not more recent synthetic cement. "Rodenstockitis" (Rodenstock lenses of a certain age range seem especially prone to this) has no visible (or at least obvious) colour cast.

Somehow, hearing your reply makes me feels very hopefully. Sadly, the adapter I ordered for mounting #00 on #0 board isn't here yet. Guess I have to wait a while longer before actually testing it out.

Once again, thanks everyone for the reply here.