Lanthanum glass in Leitz binoculars? (1 Viewer)

[Patudo]

Just happened to read a couple of articles discussing the use of lanthanum oxide in old Leica lenses (here and here, if anyone else is interested). As I understand it, these were, in effect, the ED glass of the day, enabling chromatic aberration to be reduced.

It begs the question: did any of these types of glass ever made it into Leitz binoculars? On the one hand, binoculars are low-magnification devices compared to, say, astro/spotting scopes; and the external focus systems of porro prism binoculars such as Leitz made in the 1950s, it has been said, results in chromatic aberration being less of an issue than in internally focusing roof binoculars - both of which would limit, or even eliminate, the need for ED glass (or the 1960s-era equivalents). But then at least some of the Leica lenses it went into, like the 50mm f/2.8s, were effectively low magnification devices, too; and internal focusing was one of the key innovations in the Trinovid range...


Incidentally, reading about Leica lenses makes one (well at least it made me!) wonder to what extent the optical talent at Leitz went into camera lenses rather than binoculars! I suppose there was not the same demand for quality at any price in binoculars as there is amongst photography buffs, but when one realizes that aspherical elements were being used in things like the Noctilux back in the sixties, one wonders what might have been done (and at what price!!!) had Leitz unleashed the full force of their optical talent into binoculars. What was achieved in terms of field of view by the very first generation Trinovids, for instance, is still impressive today - although I suppose with modern eyepiece designs there is less need for the complex prism-mirror combo. I'd dearly love to try a Retrovid version of those!!!

 

[Binastro]

More of a problem was that some Leica camera lenses contained thorium glass despite some at Leica denying this.

I don't know of any binoculars of any make that contain thorium glass, although it exists in military eyepieces and some Japanese orthoscopic eyepieces.

Lanthanum was used in Russian lenses, but I haven't met thorium in any Russian lens, although they may exist.

And Leica lenses were often not that great. Some deteriorated because the front elements were soft glass.
The Xenon 50mm f/1.5 was an unauthorised rip off of a Taylor Hobson lens.

Unfortunately Leica does nothing to dispel the myth that the Leica was the first 35mm still camera. It wasn't by a long shot.
Leica did not invent the 36mm x 24mm frame size.
Leica lenses were not particularly fast either.

Various high index glass was used by camera and binocular makers.

I don't think that Leitz put any less effort into binoculars than cameras or microscopes.
Generally their standards for all optics were and are high.

Regards,
B.

 

[Binastro]

Zeiss were probably using aspheric elements in lenses well before Leitz.

Zeiss were even making machine made aspheric lenses in the early 1930s.
From memory the aspheric machine was bought in from another firm.

Many lens makers were using hand made aspherics in lenses well before this.

Nikon and Canon were making very high quality fast aspheric lenses probably at the same time as Leica.

Nowadays Sony make very high quality machine made aspheric lenses.

Aspherical photographic lenses date back well over a century.

Plastic aspherics are not that old, but very common now.

The Aculons may have molded aspherics.

Regards,
B.

 

[Binastro]

So what are the problems with thorium in glass elements.

Not that bad.

But ethical considerations and possible health problems to the workers making the glass.
Also the clean up of factories with large stocks of thorium glass.
And disposal of such lenses.

In cameras the thorium lenses fog the film, although I haven't thought of any possible detriment to digital sensors, which came after thorium was stopped in lenses.

Folding cameras in particular suffered fogging.
The Apo Lanthar comes to mind.

Then lenses containing thorium rather quickly turn brown or yellow.
They can lose a stop in speed and also there is a bad colour cast.

To the user there are no real problems, although thorium lenses should not be used as magnifiers for prolonged periods.
There are now regulations regarding such lenses.

Some lenses during this period show weak radiation.
This came about because of, from memory, the use of cerium to whiten glass and not because of thorium.

I cannot remember if lanthanum lenses showed detectable readings.

Lanthanum basically just became an advertising slogan rather than any difference from other types of glass. It sounds nice.

Regards,
B.

 

[Mark9473]

Just happened to read a couple of articles discussing the use of lanthanum oxide in old Leica lenses (here and here, if anyone else is interested). As I understand it, these were, in effect, the ED glass of the day

ED glass has extra-low dispersion (hence its name) and a high Abbe number. Lanthanum glass also has low dispersion but a lower Abbe number. Look at the lower half of graph 148 in the middle of this page: REFRACTING TELESCOPE OBJECTIVE: SEMI-APO AND APO OBJECTIVES
The horizontal green lines connect ED glass types on the left with their ideal mating element glass types on the right, which include some lanthanum glasses. As the text below the graph explains: "Cancelling out secondary spectrum requires two glass elements with nearly identical relative partial dispersion (RPD) value."

This doesn't change the fact that Leica might have used lanthanum glass and other glass which isn't ED in combinations to give results hard to achieve with more 'normal' glass.