Schneider Xenotar 150mm f/2.8 redesigns/versions/variations?

[duncancmt]

I've been reading up about this lens and have heard some mumblings about one or more redesigns that went on during the len's run, but nothing specific. Do you have more information about why the lens was redesigned, when, and whether there were any significant differences?

[Jason Greenberg Motamedi]

At some point in the 1950s Schneider used some sort of glass in the rear element which had a distinctive yellow color.
Perhaps thorium glass?
I have no idea what the impact was, other than being yellow.

[Jim Noel]

Built in radio-active filter perhaps?

[Greg]

At some point in the 1950s Schneider used some sort of glass in the rear element which had a distinctive yellow color.
Perhaps thorium glass?
I have no idea what the impact was, other than being yellow.

Years ago had a German? lens that I thought one of the lens elements was yellow-orange in color, yet the image the lens projected was very neutral in color. Turned out to be a yellow-orange lens coating.

[Pere Casals]

Short answer: Using Thoriated glass was a trend in the 1950, I guess this was a WWII technology spin off, this had the yellowing drawback, so manufacturers abandoned thoriated glass (some in the 70s) because of that, I guess, but we should think if the radiactive factor was also an issue (commercial ? , manufacturing safety ? (powders)).

At the time Thoriated glass (even containing a 30% of it) offered optical/manufacturing advantages thanks to low (chromatic) dispersion and high refractive index, allowing for less curved and thinner elements.

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As coatings improved, designs with a higher number of elements became suitable, offering better correction possibilities, and of course since WWII many other high performance glass types became available.





Those Xenotars made around the 1950s had thoriated radiactive glass (in the rear element IIRC). Over the years Thorium's radiactivity tanned the glass to a tea color yellowing (provocating F-centers, https://en.wikipedia.org/wiki/F-center). This discoloration can be reversed by exposing the glass to UV light, for example several days of direct sun rays would reverse the discoloration to a certain extent. Some people place UV LEDs glowing inside the box.

This radiactivity is judged mostly safe and cannot be detected (over backgound radicactivity) at some 1m or 50cm. Eyepieces with Thoriated glass are not considered safe, but taking lenses are way less a danger. IMHO radiactive elements were discontinued because of the tanning effect. This radiactivity does not contaminate objects in contact, etc.

Rare earth glass was extensively used in WWII aerial photography optics, Aero-Ektars, I guess that this technology later ended in the civilian consumer market, it can be investigated how militar usage of thorium and its industry had an effect in the consumer industry.

There are many lenses of that era including radiactive glass:

https://camerapedia.fandom.com/wiki/Radioactive_lenses


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Lens character:

Xenotars are similar to Zeiss Plannar design.

Beyond (high) weight/size/price xenotars are sharp but Bokeh is poor, if one wants smoothness in the Out of Focus, but the large max aperture allows to defocus more background/foreground than regular LF lenses, anyway the lens won't be as sharp wide open. To me, the Xenotar strong point it's the large aperture, if one wants that.


See here the Xenotar section: https://www.largeformatphotography.i...rtrait-lenses/

[Daniel Unkefer]

Automatic Makiflex 150 Xenotar by Nokton48, on Flickr

002 by Nokton48, on Flickr

I have one in a Plaubel Makiflex automatic iris mount. I use it wide open, sometimes I'll add two 4XND filters if the light is full sun. The bokeh is interesting and I like it. This camera takes 4x5/9x12 film.

[Corran]

xenotars are sharp but Bokeh is poor,

Bokeh is not poor, especially around f/4.



Of course bokeh is somewhat subjective. For instance, Zeiss Tessars are lauded for bokeh but I find they are typically pretty busy at wider apertures. So IMO the Xenotar has much faster usable aperture with good bokeh at those wide apertures, while the Tessar smooths out at smaller stops (hence why I think the Tessar design is really good on 8x10 since it still gives thin DOF at f/11).

[Pere Casals]

Not poor, sub-poor. Hexagons with highlighted boundaries...

https://kenrockwell.com/tech/bokeh.htm

1)Poor:


2)Neutral:


3)Good:

"Fig. 3. Good Bokeh. Here is what we want. This is great for bokeh since the edge is completely undefined. This also is the result of the same spherical aberration, but in the opposite direction, of the poor example seen in Fig. 1. This is where art and engineering start to diverge, since the better looking image is the result of an imperfection. Perfect bokeh demands a Gaussian blur circle distribution, and lenses are designed for the neutral example shown in 2.) above."


"The Xenotar draws contours around everything unsharp that contrasts, thereby ruining bokeh (see Fig.10)."
https://www.largeformatphotography.i...rtrait-lenses/ , Xenotar 150 section

[Corran]

"Good bokeh" is not an objective truth (and neither is Rockwell).

Character of OOF areas also can change with aperture. The example shown on the LF article is at f/2.8, where the bokeh can be a bit busier than when stopped slightly down.

Have you used the 150mm Xenotar?

[Pere Casals]

Have you used the 150mm Xenotar?

No, and I won't, I think. In photography, there is a solid criterion about what is poor, neutral, and good bokeh. Ken explains it very clearly. One may like poor bokeh... and Triotar soap bubbles... or Aero-Ektar rings...

But what is considered a good bokeh is the lens capability to render a very smooth OOF to separate subject from background. The defocus control ring in the Nikon DC 135 and 105 is about that.

Beyond good-neutral-poor japanese artists use around a dozen adjectives to describe bokeh.

...but clearly Xenotars' bokeh is worse than Neutral, so we cannot speak about a good bokeh at all.