MC Rokkor-SI 28mm f/2.5 "radioactive" repair attem

devinw · Joined: 19 Aug 2016 Posts: 207 Location: Portland, OR

Lightshow is correct. Sorry, it's been a while and I had forgotten about that part.

The small bonded doublet is the trouble maker with the LD glass and comes out as he described. You just need to get a good grip on the subcell/tube with your hands. Nitrile gloves make this easier and are clean.

Lightshow · Joined: 04 Nov 2011 Posts: 3666 Location: Calgary

It literally took me 2 minutes to get the doublet out.

Kira · Joined: 26 Apr 2017 Posts: 3

Waouh very impressive.
Thank you very much Lightshow and devinw. Thanks to your explanations I finally succeeded.

luisalegria · Expire: 2018-01-18

Belated comment on my part, this is a very good tutorial on solving the radioactive yellowing problem on any lens.

It is surely better to remove and treat the affected group (always a doublet I think) instead of doing this to the entire lens, whether UV or sunlight treatment. This could lead to other problems through overheating, like hazing through evaporated lubricants, or as noted, possible curing effects on other cemented groups.

Lightshow · Joined: 04 Nov 2011 Posts: 3666 Location: Calgary

I believe the Ionizing radiation is causing the glass to change it's spectral character of it's optical absorption, UV reverses the process as we know.
In trying to confirm this I did find these papers:

Radiation impact on the characteristics of optical glasses test results on a selected set of materials
https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10569/105691R/Radiation-impact-on-the-characteristics-of-optical-glasses-test-results/10.1117/12.2307918.full?SSO=1

Comparison of radiation-induced transmission degradation of borosilicate crown optical glass from four different manufacturers
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.662.5624&rep=rep1&type=pdf

Radiation Induced Darkening of the Optical Elements In the Startracker Camera
https://www.osti.gov/scitech/servlets/purl/10177329-YP65hI/

danfromm · Joined: 04 Sep 2011 Posts: 591

Lightshow, thanks for posting those links.

Sorry for the belated reply.

I'm a little surprised that the OP went to so much trouble to clear his lens. I understand that many optical glasses transmit little UV. This may be a good reason for dismantling a lens to get access to the yellowed element(s). But as long as the elements outside of the yellowed one(s) transmit any UV treating for a longer time will work.

Case in point: I have three TTH tessar type process lenses (6"/9 Cooke Copying Lens, 10.16"/9 TTH Copying Lens, 300/9 Cooke Apotal) and had a 55/8 ReproClaron. All have radioactive elements, all were yellowed on arrival. I lined a box with aluminum foil (it reflected light that passed through the lenses back through them), put the lenses in it, put a 20 w UV-B compact fluorescent in reflector over the box and left the lenses to bask in the dim UV for several months. For luck, I turned them over every week or so. All cleared.

Lightshow · Joined: 04 Nov 2011 Posts: 3666 Location: Calgary

It's actually a very good lens, don't let it's current price fool you into thinking it's not a good performer.
It's well worth the effort, especially if you've opened up a lens or two to do a CLA.