Can a Leica Summitar Be Restored?

[reddesert]

Not all radiation is the same. Both the energy and the type of particle matter; particle type matters because of the penetrating power - or lack thereof. The alpha particles from thorium are easily stopped by your skin, as others said up thread. For this reason owning a thoriated glass lens isn't particularly risky. (Reference for does estimates: https://www.orau.org/health-physics.../products-containing-thorium/camera-lens.html ) But modifying it in such a way that you could ingest some of the glass by breathing (such as polishing, grinding, breaking it) is not a good idea.

The reason radon gas is of concern in people's houses is because it is a gas, and thus can migrate out of the soil into your house air, at some low but measurable concentration, and be breathed in. And people spend a lot of time in their houses so both the concentration and exposure are significantly higher than they are outdoors.

Radiation and carcinogen risk are generally cumulative - for ex, radon exposure is much worse for people who are already smokers. So "There's radon in basements anyway so it doesn't hurt any more if I grind on a radioactive Summicron" is not a valid argument. Just use the Summicron (which I realize is a different lens from the OP's lens), but don't polish it.

Disclaimer: I am a physicist, but not a health physicist.

 

[matreve]

The first two groups are air-spaced doublets.

This is the front group with the fixture taken apart, elements separated, and spacer shown.

https://rangefinderforum.com/threads/minolta-chiyoko-5cm-f2-took-one-apart.4751524/

If you look closely at the diagram from Minolta in the link, you see a Black line for the two air-spaced doublets and a white line for the cemented rear doublet. You also will note that I bought one and took it apart.

The rendering of the Minolta lens is much closer to the Summitar than it is the Summicron. The Summicron used high index of refraction/ low dispersion glass. The original version uses Thoriated glass.

Minolta, wide-open. "Swirlies" like the Summitar.



"Lens Groups are defined as being cemented, air-spaced, and oil-spaced. The Minolta Chiyoko 5cm F2 is a 2-2-2-1: 7 element in 4 groups. The 1st and 2nd doublet are air-spaced groups, the doublet behind the aperture is cemented. Air-spaced doublets allow 4 radii to be used for better control of spherical aberration. As this lens was always coated, the designers apparently felt the extra degree of freedom was worth the extra air/glass interfaces. A second reason to use air-spaced (and oil spaced) groups is to accommodate different coefficients of expansion of glass elements used in the group."

As to the brochure you posted- note the heavy black lines for the two front doublets, and the thin line for the rear doublet. Minolta is showing the air-spacing between the elements, but 70 years later- unless you take one apart you will not know why they did this.

Minolta_Chiyoko_Collection by fiftyonepointsix, on Flickr

The more common 5cm F2 that uses 43mm filters shown in this picture.

I stand corrected. Ahhh...Minolta, always surprises me.