Does the glass matter?

msbarnes

msbarnes

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I oftentimes hear "radioactive", "thorium", "rare earth mineral" and etc.

What does this mean performance-wise.

For the same/similar lens design, does this matter? Is a radioactive summicron "more desirable" than a non-radioactive one?
 
The issue for the manufacturers is getting the right optical characteristics in the glass. Radioactivity is not a desirable characteristic in a lens but the use of some minerals will give (very low level) radioactivity. The use of rare materials might give the necessary characteristics and raise the cost of manufacturing. In order to recoup that, they let the consumer know that greater lengths were gone to.

I'm not aware that within lens designs it really makes a difference. Between lens designs, it enables certain approaches to correction which might otherwise not be possible.
 
posted the same time as scrambler

posted the same time as scrambler

The way I understand it, there are two main properties of optical glass, refraction and dispersion. Refraction is how much light bends at the glass/air boundary, and dispersion is how much the amount of bend varies by the color of light. Sharper bending glass doesn't have to be as curved for a given design, and less dispersion needs less correction with other pieces of glass. Thoriated glass must improve one of these or the other, or both, but whether that makes a better lens is a different thing, imo.
 
The goals of optical design could be multiple: sharpness (close up, infinity, mid range, etc), colour correction, distortion correction, lack of vignetting, astigmatism, colour fringing, etc, speed, size, etc, etc. If you could do all that with a meniscus lens made out of Coke bottle bottom, nobody would bother with exotic and expensive materials, however the materials themselves are only a piece of the puzzle.
 
I think radioactive glass is a thing of past, isn't it? back then they didn't have optical resin widely used today to make optical elements nor CAD support to design more effective with smaller costs. High precision microscopes and similar stuff which is miles away from mass market is another thing.

Yes, expensive Leica and Zeiss glass sure is (or should be) better than common cheaper lenses but from practical point they don't have to use radioactive glass in mass market lenses to get to desired level of performance. I can be wrong, though.
 
Hi,

I'd say that the wider the choice of materials you have the more precise the design can be. And some of us like distortion free lenses etc...

Regards, David
 
I guess my question:

is a thorium glass summicron better/more desireable than a non thorium glass summicron?

I am not actually pursuing a summicron, this is just an example.

I understand that the glass and it's properties matter, but I don't pay too much attention to these types of things...should I?
 
msbarnes said:
I understand that the glass and it's properties matter, but I don't pay too much attention to these types of things...should I?
Click to expand...

When you ask "should", it seems to indicate a sense of necessity that I find curious.

Maybe the properties of the glass are things that lens designers "should" pay attention to. For we laypeople, there just isn't the same necessity.

Maybe all we need to pay attention to is the results of that: how does the lens perform? Does its rendition please me? Etc. I can't really see the benefit to me of abstracting from a complex design and manufacture process one single aspect of lens design and construction, such as the nature of the glass, and focusing on that as a matter worthy of my attention. It's enough for me just to know: how does it perform, and do I like its performance. I know I like 50 Summicrons (not that I currently own one, though I have owned Summicrons), I know I also really like Jupiter 3 and 8, for that matter I also like Elmars. And of 35s, the old Summaron 3.5 pleases me enormously. I'm not sure what I'd gain from knowing about the finer points of the glass used in those lenses. Now, I'm sure that in combination with a range of other factors, the glass will have made a difference. But for me it's enough just to know simply how it performs, and whether its performance does it for me...
Other people may well take a different view, and they may take great interest in understanding of lens manufacture. That's great - all power to them. For me, if I look at the Erwin Puts lens compendium and read that in 1950-whatever, Leica used a different kind of glass for the Summicron, it just doesn't feel like something that I necessarily "should" know, even though it's very impressive to see that Puts has that level of technical understanding of how different factors interplay. But for me - not a detail that I really care about.

Maybe the question isn't "should" you know about the glass, but do you want to? Should indicates a kind of necessity here that I'm not sure I really get. And if one does decide it's really important to know the detail about the glass, then I'm sure there are many other aspects of lens design that one would also have to take into account as well, because there's surely a delicate balance between this complex combination of factors, no?
 
I would not aim at getting a radioactive lens now. It will not make your images super-duper-sharp beyond what you would get with a lens that is free of such material in the glass. It sounds exotic to be having a radioactive lens. This is all.
 
They're not less desirable or more desirable. Rare earth elements were just a step in the progression of improving lens design. For example, Kodak, Pentax and leica used radioactive rare earth elements in several lenses. Canon pioneered the fluorite crystal element design in the 70's vintage 300 f2.8. Leica used hand ground aspheric elements in a lens I owned in the 70's, the Noctilux 50 f1.2. A lot of what was achieved by using rare earth elements like thorium can now be achieved by using modern low dispersion glass and aspheric elements made by electromagnetic slurry techniques. Newer lenses should be improved over these but not necessarily. One drawback to radioactive elements depending on the level of radiation is the darkening of the glass. I worked in the nuclear industry at Oak Ridge National Lab in the mid 70's. I had a friend who designed and built special optical systems that were exposed to extremely high levels of radiation. He said conventional glass would turn black in seconds under the levels he designed for but had special non browning lead glass with high refractive indexes he could use. One example is the sum micron with thorium and especially the kodak aero ektar of that era turned amber over the years. I've seen a few of them that were much darker due to radiation. X-ray tubes turn nearly black from x-ray exposure but this can be reversed even in lenses by exposing the glass to long periods of intense daylight / UV.

What happens is the radiation kicks electrons out of their normal stable orbit in the atoms causing the glass to turn brown. Exposure to UV gives enough energy to kick the electrons out of the unstable orbit and back to the normal level of energy. The glass turns clear again.

Simply because the designs are older I wouldn't expect a 50's 60's vintage lens to perform like a new lens but they might.
 
msbarnes said:
I guess my question:

is a thorium glass summicron better/more desireable than a non thorium glass summicron?

I am not actually pursuing a summicron, this is just an example.

I understand that the glass and it's properties matter, but I don't pay too much attention to these types of things...should I?
Click to expand...

In leica collector world, "desirable" doesnt always mean better lens. If something is rare, it is desirable even it is bad.

I have no idea about the difference in quality of the radioactive summicron here, but in case it was produced less in quantity, it could be more "desirable" :)
 
The use of Thorium was to achieve a specific type of glass. No other reason.

The radioactivity in the glass could potentially fog the film but manufacturers used lead doped glass in the rear elements to block that small amount of radioactivity from reaching the film.

The amount of radioactivity is very low and will not pose a risk to you.

Times have changed and glass with similar properties is now produced without doping the glass with Thorium.

Bottom line; No harm either way. You will not see any noticeable difference between two different lenses of the same design, one using Thorium and the other not. The goal was to achieve a certain optical property which was then achieved in a different manner without the Thorium.
 
A Geiger counter measured radioactivity in a camera with radioactive lens at our home. I gave way this camera to a museum.
 
I just remembered I have Industar L/D and what - it takes same pictures as any other lens. Probably rare Earth element in lens did matter back then, this days Sigma made their crazy 28mm for DP1 without Lanthanum and I don't feel cheated.
 
No idea about RF glass.

For (D)SLR I prefer Canon L-series lenses due to the colors and contrast they gave. Plenty of less expensive SLR lenses which are sharp, but mediocre for anything else.
Canon claims to use some rare glass elements in L series.

The only glass, which is on pair or even above Canon L-series to me is modern Zeiss glass. But I simply don't know if they use special glass for their optical elements.
 
There's RA all around us, in the ground as granite, Radon and so on and my watch has a letter "T" on it for Tritium being used on the dial and hands.

Lots of thing are harmful in large quantities but everyday in small quantities like the cyanide in apples and peaches...

Regards, David
 
Srono said:
In leica collector world, "desirable" doesnt always mean better lens. If something is rare, it is desirable even it is bad.
Click to expand...

I used the word "desireable" because "better" is even more vague...

I'm not even pursuing vintage lenses (at the moment :)).

I simply wanted to understand this radioactive stuff in more practical terms.
 
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