Arriflex History with Thorium Glass?

[McLean Goldwhite]

Hey this is my first post here! I'm really just a hobbyist film photographer looking to pick up my first 16mm camera. I gravitated toward the arriflex 16s as it can be picked up for a reasonable price (often cheaper than a bolex!), takes 100' spools, has an electric motor, and has some great glass available. Unfortunately in my research I heard that they contain thorium in the prism of the viewfinder. Now I'm ok with some thorium in a lens but having it in a part of the camera I'm ment to put right up to my eye I'm a bit less comfortable with. What I'm wondering is at which model did arri stop using thorium in the eyepiece? Was it the 16m, 16bl or do I have to look all the way to the 16sr onwards? Additionally does anyone know of any options old or modern that replaces the viewfinder of the 16s, 16m or 16bl perhaps incidentally with thorium free glass? If you have one of these cameras in your possession and aren't sure about the thorium content maybe you could just let me know if looking through the viewfinder has a bit of a brownish-yellow tint? Thanks!

[Aapo Lettinen]

Don't know about the thorium history of these cameras but if there would be any in the visible outermost glass surfaces it would be very easy to detect with a geiger counter. If it would be in the middle, the glass surfaces would block the alpha radiation the thorium generates and the ratiation level should be neglible or even undetectable. It is this way with lenses like super takumars. Radioactive but easily blocked. I have understood that in most cases the yellowing is happening in the canada balsam surfaces and not the glass itself and it is not happening in all lenses at the same pace

[Dom Jaeger]

Where did you read that the viewfinder prism of an Arri 16St contains Thorium?

I don't know whether it's true or not, but the prism itself is quite far from the eyepiece. It sits at the front of the camera, next to the reflex mirror, at the far end of the viewfinder tube from the eyepiece. So I wouldn't worry about your eye being close to it, you'd be a good 6 or 7 inches away. 

All those news cinematographers who spent years peering through a 16 St don't seem to have all collectively died of radiation poisoning or brain cancer, so I would say that even if there is Thorium present, the occasional use by a hobbyist wouldn't be dangerous.

[Simon Wyss]

The radiation is quite weak. More and dangerous radiation would only be set free upon literally working the glass, machining it or grinding on it. One would then need to breath the dust in.

I wrote about Thorium oxide alloyed glass in an article about the Arriflex 16 on a German forum, September 2019. The text is also downloadable from my website. I have begun to translate it to English but not finished, yet. Alpha radiation can easily be shielded off within an inch.

The yellow stain does not stem from Thorium oxide but from Cerium oxide which accompanies it, a contamination. For more information there are Kodak publications on the glass used for the Aero Ektar and more reconnaissance optics made from 1940 on.

https://www.nro.gov/Portals/65/documents/history/csnr/programs/docs/Bridgehead Eastman Kodak Company.pdf?ver=2019-03-29-103653-233&timestamp=1553870223588

https://www.dpreview.com/news/8448160792/humor-the-horrifying-truth-about-radioactive-lenses

[Dom Jaeger]

36 minutes ago, Simon Wyss said:

I wrote about Thorium oxide alloyed glass in an article about the Arriflex 16 on a German forum, September 2019. The text is also downloadable from my website. 

How do you know Arri used Thoriated glass in the Arriflex 16S viewfinder prism Simon? Do you have a source reference? 

Perhaps someone has measured it with a Geiger counter?

[Simon Wyss]

I don’t know for certain, it’s an assumption. Having met yellowish glass in the Zeiss-Ikon Movikon 16 and read about higher refractive optical glass with a yellowish to brown stain I concluded the use of Thorium oxide glass when I worked on an Arriflex 16 ST finder.

Completely open to enlightenment in the case of yellow-brownish glass

[Aapo Lettinen]

thorium glass is very easy to detect with a geiger counter, even with a model which is mostly sensitive to gamma and beta rays. when brought close enough to the glass the counter will go nuts if it contains thorium. If it only has couple of extra ticks over the background radiation then it probably does not have any thorium in the glass.

any material between the counter and the glass blocks some of the radiation and if the prism is inside a camera you may not detect anything at all. If there is a direct line of sight to the glass surface or there is nothing more than a plastic lens cap or similar in between, then the counter should have A LOT higher reading than the background radiation is (it goes from couple of ticks per second to thousands or tens of thousands per second. cannot miss it)

[McLean Goldwhite]

Thanks for all your replies! Knowing that the prism is towards the front makes me feel a lot better about picking up a 16s though I'm seeing a few good deals on newer arriflex models I might jump on. I might buy a cheap geiger counter and update this thread once I get a camera and test it. My guess is around 1970 is when they stopped using thorium but that leaves the 16bl in limbo being released in 1965 so close to the 70s. Either way it should be helpful for folks to know (either confirming that the 16s has thorium but that little to none escapes or showing that some newer model is free of thorium indicating newer than x model if thorium free).

[Simon Wyss]

Wait, it seems we’re confusing parts. First it was about a prism made of Thorium glass, then an eyepiece. If at all, it’s about two thick positive lenses cemented to strong negative ones as I have depicted. For a prism there’s no need for an elevated refractive index.

[McLean Goldwhite]

Ah I see! Thanks for the diagram Simon! Still it seems that those lenses are far from the eye so that's good. If I end up picking up a 16s it would be interesting to run a geiger counter along the tube and see if it picks anything up near those elements. Your findings that it has a yellowish-brown tint means its very likely thorium. I don't know of any other additives with that distinctive color that would have been used in a lens at the time.

[Aapo Lettinen]

if you need to shoot with the 16s then there is nothing you can do whether it having radiation sources or not. Personally I would not worry about it unless wanting to take out the glass elements and grind them to dust...

just for the fun of it, I tested my Super Takumar 55mm F1.8 again with the basic geiger counter I have. You have to take the counter very close to the lens to detect anything (just like a spherical light source, the intensity lowers very quickly when distance is increased) . if you want to be couple of centimetres or millimetres from the lens elements then you can get a high reading. from 20cm away the radiation level is very minimal.

And as said, the glass elements block most of the radiation. The "hottest" part of the lens is its back part where the thorium containing elements are most exposed. Most of the elements don't contain any thorium 

Background level:

 

Directly over the front element:

 

 

 

[Aapo Lettinen]

Over the back element with plastic lens cap on:

 

Back element from half a centimetre away with no lens cap:

 

 

A 8mm thick glass filter simulating how much radiation is blocked by a glass element. compare to the previous pictures.

 

 

[Aapo Lettinen]

btw, everything around you including the air you breathe and even yourself are radioactive. it is completely natural and I would not worry too much about it unless you are going to eat or drink something excessively radioactive or will going to inhale radioactive dust. 

In the case of the film camera viewfinders, I would worry if one would take out radioactive elements and glue them to their eyes so that they would carry them on their person 24/7 for many years. I would expect some kind of eye radiation damage from that kind of use but if only using the camera like it is intended to be used, then should not be much of a problem

[Aapo Lettinen]

from about 30cm away it is very difficult to detect the unexposed back element of that Super Takumar 55/1.8 with that geiger counter I have. So to detect anything you need to be very close to the glass element and it needs to be unshielded or very lightly shielded. 

[McLean Goldwhite]

Yeah I agree it's not realistically much to worry about but a large part of why I enjoy shooting on film rather than digital is the experience. I like slowing down and taking my time getting to know a camera and I think it might feel a bit bad sometimes to know I'm playing a few more rounds of (albeit low risk) russian roulette with my cells while near it. I understand that some types of radiation (depending on the momentum of the particle) can pass through your body and that it has an extremely low chance to cause damage in the process. Getting material inside you that is continually emitting radiation is a much more dangerous scenario (closer to your hypothetical of glueing a radiation source to your body). I think I'm just an overly cautious person by nature who tends to look into minimizing risk so these thing come up in my consideration. ?‍♀️

Edited June 20, 2021 by McLean Goldwhite

[Simon Wyss]

Be allowed the question why an Arriflex 16. You can avoid radiation with a camera and optics that don’t contain Thorium, that in addition accommodate your wish for slowing down. Bell & Howell and Paillard-Bolex H cameras have critical focusing aids built in that allow to frame and focus down to until the object touches a lens’ front. The system is free from problems inherent in reflex finders. Yes, reflex viewfinders have some drawbacks such as physical constraints to lenses, elevated price, fragility (pellicle) or the optical implications of double prisms.

There are more cameras which have a critical focuser but no rackover accessory was ever offered. The French ETM P 16/9.5 for example has a finely grained ground glass and a retractable periscope. A very rugged camera.

Victor are underrated in my opinion. I’d like to point out that they bear lens mounts somewhere between the Bell & Howell A and B mount meaning that old lenses can be used. A technical detail: the cylindrical section ahead of the camera thread is not cylindrical but slightly deformed to a triangular roundness. That way a lens is rather snugly centered. A technician should be able to measure and adjust the brass ports. I have written an article about the Victor models 3/4/5, the translation isn’t finished, though.