yellowish cast looking through 35mmf1.4

Greetings - I've just purchased a nikkor 35mmf1.4 AI that exhibits a

noticeable yellowish cast when looking through the lens. Have others

seen this with theirs? Is this something that can happen from age?

What filter might correct this? Thanks for your help.

I don't know if this answers your problem or not, but there's been a fair amount of traffic lately about a discovery that you can "clear" yellowed radioactive glass in some early high performance lenses by sitting them in direct sunlight for about a week. wrap the lens in aluminum foil to minimize heating, leaving the glass exposed, and set it on a windowsill in the sun. Word has it that if the problem was radioactive yellowing, it will be clear as new in a week.

 

I haven't tried this myself, but the sources seem pretty reliable.

 

rick :)=

I don't think that Nikon ever made a radioactive 35/1.4.

There have been four versions of the Nikon 35 mm f1.4 lens. The first version is labeled "Nikkor-N" and has a metal scalloped focusing ring. This version contains glass with radioactive thorium. I have measured the gamma-ray spectrum of this version and the resulting spectrum shows the presence of thorium with more certainty than a fingerprint identifies a person. The currently produced AIS version is not radioactive. I have not measured the second and third versions.

 

Thorium-containing glass was used far more commonly than is generally thought. Numerous manufacturers used this glass in many different lens types for its desirable optical properties. Today glass without thorium that has similar optical properties is used instead. I have written about thorium glass in my webpage on Aero-Ektars: http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html

 

The color cast, which is usually called yellow, seems more like brown or the color of tea to me. It originates from "color centers" that are formed by the passage of the high-energy radiation. I am one of the people that have reported that the color can largely be removed with UV light. I have been experimenting with the BLB fluorescent blacklight bulbs. These are sometimes used at parties and are readily available. With these bulbs exposure times of weeks will mostly clear the color. This method might be easier for people who don't have reliable sunlight or a safe location to expose a lens to sunlight.

 

Since the brown color looks fairly similar to a warming color correction filter, adding a blue color correction filter might create a fairly neutral color rendition. Of course, the reduction in light throughput would make the use of this fast lens pointless -- it would be better and cheaper to use a slower lens without the color. For B+W work the color doesn't matter as much, but is still reducing the light throughput.

Are you sure this isn't a result of the single coating? Some old single coatings look yellow. My 50mm f1.4 Nikkor-S has a yellow cast, but it has yet to show up on film, so I've just ignored it.

The aluminum foil isn't to protect the lens from overheating. It's to keep the CIA from finding out what you're up to.

 

Lots of older coated lenses were yellowish when new. My old Zuiko 75-150/4 has a slightly yellowish single coating - never shows up on film, even slide film.

 

Way back when Canon made a 35mm lens from exotic Mysterium with a concave front element that is noted for having turned yellowish with age. Some folks are more concerned with getting brain cancer from proximity to the radioactive Mysterium than with color casts on their slides.

 

You could slap a light blue filter over your lens. The combination would produce a lovely green, similar to the distinctive metallic green hue of later Nikkor multicoatings.

Michael,

 

thanks for passing on that info - very interesting! I have a couple of related questions(sorry to diverge away from the original posters' question!) :

 

I sometimes leave film in the back of my cameras for months at a time... How long,roughly,would it take from film(lets say 100 iso for sake of argument) stored in the back of a camera with such a radioactive lens to show signs of the radiation damage? and...

 

I have an old Canon 50/1.2 Asp. ,which i suspect may have a Thorium element or 2 in it,which i plan to use for long exposure(up to 1 hour to start with) astrophotography. During the exposure,since the shutter curtain no longer protects the film,there would be a significant increase in exposure to alpha and beta particles(as well as the already present and unstoppable gamma rays.

Have you any idea if this could significantly fog the film?

 

Thanks,

Leo

Leo: The thin foil shutter curtain is not going to shield the film from the gamma rays to any significant extent. Radiation exposure is going to depend heavily on the distance from the source (the thorium element) and its intensity. I've done some autoradiography of radioactive foils using 400 speed B&W polaroid film and I would find a 5 second exposure sufficient for a contact reading of 1 mSv/hr. However, this field falls off very quickly with the square of the distance and is probably 100-1000x more intense than most radioactive lens elements. So I probably wouldn't worry about it.

 

Michael: thanks for the info on the Nikkor-N 35/1.4.

In order of probability:

 

The old multi and single coatings(they changed it somewhere in the AI period) was blue/purple, the later AI and AIS models have a green coating. You have OR a modern(yellow-green) coating or the old blue-purple coating has been dissolved using chemicals to clean the lens(sometimes ppl do that so coating scratches wont show, grrr...). Optical glass has a typical yellow-greenish color due to iron contamination of the glass. Any coating has a oily shine when you look at it under a certain angle...

 

Nicotine can also cause coloration of the lens, which is also yellow or yellow/brown.

 

Aging balsem used to glue the glass elements can turn yellow in time.

 

Your lens probably does not have any radioactive elements, in the seventies any radioactive contaminations were no longer allowed, exept in some military equipment. AFAIK Nikon used some radioactive stuff in their first ED glass experiments and on the first Noct-Nikkors. Old Leica glass from the fifties often is radioactive. Its easy to check if your gear is radioactive, most schools have the equipment to check for radiation. If you have a optics collection from before the seventies(Leica users/collectors pay attention!) you would be wise to have someone check them for radioactive contaminations.

 

Read more about radioactive optics here:

 

http://medfmt.8k.com/mf/radioactive.html

 

Greetings,

Regarding Thorium contaminated glass(most common radioactive glass) can be quite easily spotted because the glass turns brown in time due to radiation damage. The glass looks brown/amber and is darker/more intensely colored in the center of the glass(where it is thicker). I got this from the link in my previous post, im going to check my lenses RIGHT NOW ;)

A yellow-tinted AR coating will look yellow only in reflection, not when looking through the lens at a white background.... this would be an easy way to check whether the color you see is in the coating or in the glass.

 

:)=

I had an older version of this lens (Nikkor-N.C 35mm f/1.4 non-AI, f/22 minimum aperture, 7 bladed diaphragm to be exact :) ). It had this very same feature (or problem).

What might be of interest to some is that this yellowish cast showed up in an entirely different way on different kinds of film. With Provia 400F it was sometimes simply ugly (yet on some pictures it could not be seen at all!), with Velvia I found it to be absolutely acceptable (in some cases it acts like a "warming" filter..) , and it was OK with Provia 100F too. I hadn't tried it with other kinds of transparency films, and with B&W there are no problems at all, of course.

I wish I had learnt about this "UV-cure" earlier, as apart from this yellowish cast (and its distortion and weight..) I really loved this lens, but I sold it and bought an AF 35mm f/2..

I would have guessed that the shutter of a 35 mm camera would barely attenuate the radiation, but I would have guessed wrong. Measuring 35 mm f1.4 Nikkor-N with a Geiger counter positioned just behind the rear of the lens obtains 2100 counts per minute (compared to a background rate of 30). Placing the lens on a Nikon FE and measuring the rate through the film gate with open shutter gives a reading of 700 counts per minute -- the reduction is mostly from the

increased distance from lens to the Geiger counter. When the shutter is closed the rate falls to 500 counts per minute.

 

The reason for the modest attenuation is that the radiation has a complicated spectrum, including both relatively low energy radiation that is easily stopped and high energy radiation that is highly penetrating. Predicting the radiation is difficult because of the complicated spectrum of thorium and its daughters and because we don't know which glass element contains the thorium and therefore we don't know how much self-shielding in occurring in the lens. The radiation field close to the lens doesn't simply follow the inverse square

law because the lens is larger than a point. Also, if any alpha particles escape the lens, they will be absorbed even in a few cm of air.

 

I haven't experimented with these Nikkors, but I guess that film in close proximity for days might acquire a significant exposure. My guess is based on experiments with a 7 inch Aero-Ektar, which is several times more radioactive. A 13 day exposure of Delta 400 very close to the "hottest" exterior part of the lens caused a very noticeable density. Probably using the lens for a few hour exposure would be ok -- between the shorter exposure and the increased distance from the film, there would probably be negligible fogging. I wouldn't leave the lens on a camera containing film for many weeks. These questions suggest obvious experiments......

 

I do not understand someone saying "Your lens probably does not have any radioactive elements" because "in the seventies any radioactive contaminations were no longer allowed" when I had already reported actual measurements of radioactivity from a Nikon lens made in the early 1970s. We do not know whether Bing Huey's lens is radioactive -- he has not reported which version of the Nikkor 35 mm f1.4 it is. If he has the first version, it is very likely to be radioactive, since his lens has a yellowish cast and I have measured radioactivity from lenses of this version. I have now measured three of the first version (two labeled NIKKOR-N and one NIKKOR-N.C) and all three have

significant radioactivity. It seems likely that all lenses from the first version are radioactive.

 

Peter Braczko in "The Complete Nikon System" says that the first version was shown in 1970 and produced from March 1971 to 1976. The webpages of Roland Vink have information about the various versions:

http://home.aut.ac.nz/staff/rvink/nikon.html and http://home.aut.ac.nz/staff/rvink/nikon3.html. He calls the first version type "C" and lists three variants in the labeling. One of his photos, http://home.aut.ac.nz/staff/rvink/c3514c.jpg, shows the amber cast.

 

The webpage http://medfmt.8k.com/mf/radioactive.html is a collection of writings of many people (including myself). It has much good information, but it also contains just plain wrong information. For example, the idea that the radioactivity is from contamination is a wrong. Based on technical literature from the time period, there is no doubt that thorium was intentionally included in optical glass. Measurements of the radiation level verify this. See my

Aero-Ektar webpage: http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html

Thanks to all for the informative responses, especially to Michael Briggs for his extensive discussions. The lens I have is an -N.C version and therefore is most likely thorium-containing. I suppose the thing to do is to always pack and carry it a foot away from anything and anybody I do not wish exposed. The question now is what it would take to eliminate the yellow cast. Here at work we have a UV-crosslinking chamber and I have tried three rounds of irradiation through each end of the lens at 7000 microJoules per round. The color remains. How does this compare to the energy it would receive through a window for a week?

I have made a very rough estimate of the solar UV flux that a 35 mm Nikkor-N would receive in a week: From the solar spectrum at

http://isccp.giss.nasa.gov/pub/documents/b3n-071.pdf, I roughly estimate the energy flux in the near-UV, 300 to 400 nm, as about 100 Watts per square meter. This is about 5% of the total flux, the "solar constant" of 1370 Watts per square meter. Using the area of the lens, the UV flux is about 0.1 Watts. The UV flux will decrease when the sun isn't high in the sky, so using four hours per day for 1 week, this would be roughly 10,000 Joules (note: 1 Watt = 1 Joule per second). This is obviously far more than 0.04 Joules from 6 rounds in the UV-crosslinking chamber.

 

Another issue is the wavelength of the light from the UV-crosslinking chamber. If it is short-wavelength UV, it might be ineffective. While short-wavelength UV should be more effective at bleaching the color centers, as the wavelength becomes shorter, the optical glass and coatings start to become opaque to it so that the photons won't reach the color centers.

 

My experiments at removing the color-cast of thorium-glass have been done with fluorescent blacklight bulbs, type BLB. These emit long wavelength UV and are sometimes used at parties or for other amusements. I found some inexpensively at Walmart. While these bulbs probably give less UV than the sun, they can be run 24 hours a day. I also find this method more convenient -- others with a south facing window and frequent sunny days may find the sun easier. The unfiltered type BL bulbs should work better and are said to be cheaper, but I haven't found them locally. For all about UV light sources, see the article by Sandy King at http://unblinkingeye.com/Articles/Light/light.html.