A stain inside sekor 180mm - is it oil, separation or what?

<p>Hello,<br>

just bought a Mamiya Sekor C 180mm at a big auction site. The outside condition of the lens/glass is indeed mint, with no scratches or anything, but inside the lens I have noticed a stain along the edge of the glass. Looks like some transparent oil squeezed between the inside elements. The shutter/diaphragm seem ok, with no oil on blades. could anyone please comment as to what it is and how difficult/expensive it is to clean? I may request a refund from the seller, since it is an obvious defect that has not been described in the listing. Thanks in advance for your time and comments.<br>

<img src="http://mphoto.puslapiai.lt/sekor/DSC_3071.JPG" alt="" width="800" height="800" /><br>

<img src="http://mphoto.puslapiai.lt/sekor/DSC_3090.JPG" alt="" width="800" height="800" /></p>

Have you tried taking pictures with it ? My guess is the lens was taken apart and lubricated prior to the auction leaving oil residue.

<p>no, I haven's taken pictures with the lens. but it is obvious (not from the attached pictures perhaps, that the image quality would suffer with wide apertures). It is just that I have a few days to decide whether I keep it or return it, and since I have never seen anything similar on any of my lenses I am pretty curious. I would not bother with this one and return it immediately, but its overall condition is really superb, so I thought maybe it is something that can be easily fixed? speaking of lubrication - I may sound silly, but... is it a common practice to take a working lens apart to lubricate it? I've seen fungus, dust and some other problems, but never saw this kind of trouble. And sure, the lens was described as clean and clear (a seller has good feedback), so maybe something happened to it during the transportation?</p>

<p>It's not possible to be certain from a photo but it could be separation. The small indentation in the "stain" at 10 o'clock in picture 2 is characteristic of separation.<br>

Until I noticed the indentation I wondered whether the previous owner had tried to clean the rear surface of the rear element but had missed part of the edge for fear of damaging the shutter blades. As you will have seen by now the shutter is behind all the glass.<br>

People have been known to add oil to a partially-separated couplet to improve its appearance & performance by removing the usual "rainbow effect."<br>

Whether I would return the lens would depend on the price paid - but then I'm an ex-repairer so am able to repair it myself. If I had paid a normal price for the lens I would certainly return it.</p>

<p>Thank you. It's certainly not related to the cleaning of the rear element - it is crystal clear and the whole trouble is inside the lens. The price paid was high enough, so I believe return is the option.</p>

<p>Look like separation to me. It probably won't noticeably affect your image quality, but I would return it, given that you bought it under the impression that it was in good condition.</p>

<p>It's separation of the elements. I've come across two RZ lenses with exactly that problem.</p>