Re-cementing of Raynox Polaris Auto Zoom 70-235

macheck · Joined: 30 Oct 2013 Posts: 131 Location: Poland

I have a Raynox Polaris Auto Zoom 70-235 mm f4.5 but it was in pieces (outer barrels removed and almost no screws, tripod thread insert and part of M42 mount missing, with front group element partially delaminated. Bought it for experiments and spares with rather no hope for restoring it but when it arrived it was almost complete so I decided to rebuild it. Unfortunately I have no pictures of it when I acquired it. The front group was damaged because someone forcefully tightened its assembly barrel without noticing that it was misaligned, apart from delamination, the third element is chipped slightly - still fragments of it were inside.
I knew that cementing is done with the use of canadian balsam but I had no experience and no balsam and a strong feeling that proper re-cementing is rather impossible at home for DIY man. So I assembled it without cementing front lenses (there were Newton rings visible in light through observation) took some pictures with it and lost interest of it.

Reading thread:
http://forum.mflenses.com/re-cementing-doublet-elements-with-canadian-balsam-t34467,highlight,%2Bcementing.html
Jon Goodman proposed the idea of doing it at home even with rosin some of which I had, so decided to give it a try with my lens.
I have to say that lens re-cementing is simple but the outcome might be disappointing.
I did several attempts firstly just putting lenses in the oven (temp. about 80 deg Celsius) with solid rosin in between but there were a lot of air bubbles after rosin melted and the bonding layer was rather thick. Others were done with rosin dissolved in ethanol. Keeping in mind that the process of curing might take months I decided to keep the dissolved rosin as thick as possible (even I did use microwave oven to evaporate alcohol which might be very dangerous since flammable vapors are produced - but it is very effective). With the rosin thick as very thick honey (when cold) the process of lens cementing is impossible since the layer of it is also thick and with air bubbles. I ended with oven heating both lenses and the rosin to about 80 deg Celsius then removing everything out of oven and pouring some rosin on concave surface of one lens and quickly covering and applying some pressure to remove the excess of it. Afterwards after inspecting the bonding layer for air bubbles and even some impurities which might be trapped in between I did leave lenses to cool down but the lenses were sliding on each other since the adequate leveling is very important, the thing that was not put forward by Jon of even French source that he mentions.
Without leveling even after careful centering the top lens have a tendency to float to reach the equilibrium even after they are cooled and left for days. The curing might be endless but after ten days I decided to assemble the lens - I am rather impatient. My first attempt to remove the excess of rosin with alcohol ended in a failure since it got into bonding layer and spoiled whole thing. In another attempt I cleaned front and rear surfaces with alcohol but sides were cleaned mechanically in order to avoid any liquid penetration also no sides black painting.
I didn't take a lot of pictures since had no help and was concentrated on the process.

The front group lenses and rosin solution:

The re-cemented lenses, on a leveled "platform" one can observe the excess of rosin:

The lenses after some days and cleaning, the chipped third lens and casing elements are visible:

The front group assembled:

The lens, one can observe in the reflected light the Newton rings, I think the bonding rosin layer is too thin, so the whole thing should be repeated maybe with less pressure when gluing together or something else but since it is an experiment I left them (they are not visible in through light passing lens observation), some perimeter damage of outer coating was there when I obtained the lens:

The picture taken after re-cementing and some lens adjusting:
f4.5, focal length - 235 mm:

f8, focal length - 235 mm:

I will obseve the re-cemented element if any deterioration will occur since I do not know if rosin bond is long lasting one.

Macheck