Re: One way to fix lens separation
Quote:
Originally Posted by
Dan Fromm
I was going to start a new discussion but since this one's been revived -- thanks, Albert -- here goes.
Years ago I was given a 58/5.6 Grandagon ex-Graflex XL. The glass was clean in the sense that there were no scratches or fungus but both cells had major separation. Both had rings of fire around the periphery, the rear cell had silver spots near the center. Many Rodenstock lenses from that era have similar separations.
I tried it out anyway. It shot quite well and is one of the shortest lenses that will focus to infinity on a 2x3 Pacemaker Speed Graphic. Unfortunately putting it on the camera is a pain because the rear cell is too large to pass through the front standard. The procedure is: unscrew rear cell, attach board with shutter and front cell to the front standard, put the rear cell back in the shutter from behind the camera. Reverse to take the lens off the camera.
After I got 65/8 Ilex that went on the camera without all that fiddling I put the Grandagon in the drawer. I recently took it out. It seems to have healed itself. The rings of fire are nearly gone and the silver spots in the rear cell are nearly invisible.
This is not supposed to happen. Separation is permanent. Do any of you have badly separated lenses that seem to have healed?
I'm hoping that the bad lens separation will turn out ok. So far so good, and I will move on to cementing the lens next after a light cleaning and feather light polish.
Quote:
Originally Posted by
Albert A.
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Re: One way to fix lens separation
I have done this many times in the past, but have never used water, instead used cooking oil. I found that oil held the head (up to about 300F) without burning and you could leave the elements in the oil until everything cooled down to room temp without danger of hurting the glass. The oil also appeared to have some solvent properties that made either balsam or epoxy come off easily. I use either brake cleaner or acetone to clean the lenses once cool, then UV cement to recement. I have a project coming up in the next month to do a hasselblad 120 s planar with front separation.
Re: One way to fix lens separation
Obviously works in a pinch, but a more robust method:
100 parts Methylene chloride. 15 parts methanol, and 3 parts ammonia (26% conc) is a gentler / better solvent for removing balsam and uv adhesives. Balsam takes about 1-2 days. Modern stuff takes 1-3 weeks. No risk of thermal shock / stress with this concoction, and a new bond joint will last much longer than reflowing the old. As a lens designer I can say your luck successfully separating as described will not last forever.
Btw re-cementing a lens with UV or other modern adhesive when it originally used balsam may noticeably change the optical performance.. especially true in faster optics. Just so you’re aware. Best to use like-materials to repair.
Speedball India Ink painted on works fine for edge blacking.
Re: One way to fix lens separation
I've a big Ektar that needs this treatment; where are you getting your Canadian Balsa, Kramer?
On reflection, I think I have a jar of this I bought for use in an oil painting medium.
Does age matter if it's still clear?
Cheers
Re: One way to fix lens separation
Methylene Chloride (Old fashioned paint remover) is a very nasty item(for the user) and is no longer available in most parts of the world. And the inclusion of ammonia reminds me that I have lost two lenses to devitrification when using aqueous based separation well away from pH 7!
Canada balsam looses its solvent. - even in well sealed containers. If it remains only slightly yellow, it can be made more fluid (ad libitum) using xylol.
The easiest source of CB is in drop spout equipped small plastic bottles made for slide preparation by microscopists.
There are longer - and better!- threads about separation etc. here. I would describe the first part of this thread as promoting a very dangerous and shoddy method.
Re: One way to fix lens separation
How do you know you have lens separation? What does it look like?
Re: One way to fix lens separation
Quote:
Originally Posted by
Alan Klein
How do you know you have lens separation? What does it look like?
The classic manifestation is Newton's rings. Look it up.
Re: One way to fix lens separation
Quote:
Originally Posted by
Steven Tribe
Methylene Chloride (Old fashioned paint remover) is a very nasty item(for the user) and is no longer available in most parts of the world. And the inclusion of ammonia reminds me that I have lost two lenses to devitrification when using aqueous based separation well away from pH 7!
Canada balsam looses its solvent. - even in well sealed containers. If it remains only slightly yellow, it can be made more fluid (ad libitum) using xylol.
The easiest source of CB is in drop spout equipped small plastic bottles made for slide preparation by microscopists.
There are longer - and better!- threads about separation etc. here. I would describe the first part of this thread as promoting a very dangerous and shoddy method.
Agree on all accounts..though the concoction is straight from Norland and my experience in the optical shop doing this is a bit different than yours (if you do the math, you find it’s only 0.78% ammonia)
Re: One way to fix lens separation
Quote:
Originally Posted by
Dan Fromm
The classic manifestation is Newton's rings. Look it up.
Yes - for modern UV synthetic glues where there are very small distances between the hard glue surface/air space/lens surface.
NO - for Canada Balsam separation. The balsam never becomes a homogeneous solid, so separation is gradual. Some solids are deposited , which can give a general yellowing to the edges.
Re: One way to fix lens separation
Quote:
Originally Posted by
Steven Tribe
Yes - for modern UV synthetic glues where there are very small distances between the hard glue surface/air space/lens surface.
NO - for Canada Balsam separation. The balsam never becomes a homogeneous solid, so separation is gradual. Some solids are deposited , which can give a general yellowing to the edges.
We both missed another manifestation. I once bought a 16/2.5 Zeiss Luminar -- yes, this is a large format lens -- that appeared to have been baked while vertical. There was balsam puddled around the front element and visible voids between the cemented elements.