Balsam fault along edges of 360mm sironar

[tor kviljo]

Hope someone can help me with this one: I have on hand a nice 360mm Sironar (older version - serial # about 6 mill, all black but to old for MC) f 6.8in Copal for a very good price. The price reflects that there is separation continuous along the edges of the (very large) front element. Separation is about 5mm wide. Not an unknown feature of many Rondenstock lenses I understand, but I have not had any lenses with this problem before. What I would like to know - before spending time & film testing it - is if this fault is degrading image-quality over all f-stops, or if the effekt of edge separation will decrease when stopping down. Do I recall right when I assume that the rays from the outermost edges of the lens is not image-forming when using the lens stopped down? I hope (if usable when stopped down) that this lens could substitute for my highly missed 360mm Nikkor W. Do anyone have a thought about the quality of the sironar 360 vs. the nikkor-w 360?

[Eirik Berger]

Myyyy precious....
You will never ever get it back, cause it´s MINE!!!!

[tor kviljo]

ahem! - have to explain.... Eirik grabbed that 360 Nikkor-W of mine - just becauce I were out of cash a little while (##¤%"&!!!)

[Bob Salomon]

Tor,

6,000,000 makes the lens a 1966 version.

Sometime during that time, for some reason, the pitch that seals the element edges developed a slight hole. The most common cause of this happening is from rough handling. This very small hole allowed moisture to seep in between the elements and this in turn caused seperation.

Nothing can be done to restore a lens this old to it's original condition but the effect is probably only minimal at this time.

However the ring will keep on increasing over time until it may get to a point that materially effects the performance of the lens. But since this lenses is approaching 40 years old it problay has many good years left in it. Just bear in mind that this lens is not designed for wide open applictions. It works best at 22 to 32 on 8 x 10.

[James E Galvin]

It's not difficult to recement the lens. See S.K. Grimes site. I've done it for several lenses.
http://www.skgrimes.com/index.htm#nav

[Steve Hamley]

Adam at S.K. Grimes no longer recements lenses - or at least he recommends sending them to John van Stelton at Focal Point. The price last time I checked Focal Point was $180 per cemented pair. So $180 for one plasmat cell, $360 for a Dagor, etc.

Steve

[Oren Grad]

I doubt that it's worth re-cementing a 360 Sironar when, with a bit of patience, you can find a clean 360 Sironar-N or Caltar IIN, which is a substantially better lens and fully competitive with your old Nikkor-W, for $400. Unless, of course, there's something in particular about the look of the older lens that you especially like. But it doesn't sound like that's the case here.

[James E Galvin]

There is some info on Grimes site on how to do it (in old news). See his procedure, then: I do it a little differently: seperate the elements by soaking in MEK (I don't like to heat the elements, danger of cracking unless you have experience). The soak might take a week or two. Instead of V-blocks, I use 3 microscope slides taped together to make a "fence" and hold it to the lens with a rubber band. After the cement spreads, apply the slides and rubber band, I line up the rubber band with the joint between the glass pieces, feel around to make sure its centered, and give it 5 minutes of UV. The cement is now gelled, and you can take the fence off and clean up with a paper towell moistened with MEK. If there is a problem, a short soak in MEK will take it back apart. Then put the fence back on, and give it the final UV cure of an hour or two. The hard part might be getting the element out of the mount. If you are lucky, unscrew a ring and it comes out. If it is turned into the cell (a narrow lip folded over the glass) then use some care with a jewllers screwdriver to unfold it, a very little at a time, so as to not chip the glass. Fold it back with a piece of wood or plastic (you will slip, and a metal "folder" will scratch the glass.

[tim atherton]

Richard Knoppow recently posted on re-cementing on the LF mailing list

http://www.pairlist.net/pipermail/largeformat/2005q3/019094.html

http://www.pairlist.net/pipermail/largeformat/2005q3/019095.html

http://www.pairlist.net/pipermail/largeformat/2005q3/019096.html

http://www.pairlist.net/pipermail/largeformat/2005q3/019087.html

and the Grimes info Jim talked about:

http://www.skgrimes.com/popsci/index.htm

[Ole Tjugen]

Jim, what is MEK?

I have an 1870's Steinheil Aplanat with severe separation which I'd like to get recemented...

[James E Galvin]

Several solvents might work, I have used MEK methyl ethyl ketone, available at a paint supply store. It is flammable (very) and toxic, use with ventillation: outdoors. A glass or polyethylene container, or metal, should be used, it disolves many plastics. Try it first.

[tor kviljo]

Seems I have the option of using it & obtaining OK images when fault is small - and trying to recement it when problem arises. Thanks to all for valuable info!!!