Archive | April 2016

Will the real infrared photography please stand up?

b-w_ir_filters

The strange thing about infrared photography is that it represents a very small piece of photography in general, but there is apparently no space in photography so small that it can’t support some form of snobbery. And in infrared photography, it is the idea that there is “near” infrared versus “true” infrared. Not only does this convey a false sense of exclusiveness to people who shoot 850nm and up, it’s also not accurate.

When you shoot a normal camera in daylight, there is a small amount of infrared contamination – it’s about 10 stops less than daylight, or coming in at 1/10 of a percent or 1/1024. Tiny, even on something with big infrared contamination like a Leica M8. So any particular shot is overwhelmingly lit by visible light.

A dark red filter (RG630, 091, 8x, #29, etc.) flips the equation: the average blockage of visible light is 3 stops, or 75%.The reality is that most skylight scenes are predominantly blue, and this filter cuts a lot more than three stops. Even if you are shooting objects that are middle grey, these filters reject 75% of all light – meaning that when you shoot them on a camera with no other IR rejection, deep red and infrared light make up 75%+ of the light. The false color you are obtaining is infrared light that is still being blocked in part by green and blue squares on the Bayer filter on the sensor.

The case for the “near” classification is even weaker with the 695-720nm filter (RG695, 092, R720). First, consider that wavelength ratings on filters are at the 50% mark. So a 720nm filter really starts passing 100% of its light around 750nm. On a short exposure, which you will see is commensurate with a normal visible-light exposure, infrared light is providing almost all of the illumination.

Going the other way, “true” infrared is not that advantageous – and may not be something to commit to in an IR conversion. First, even though the Bayer filter does not affect 830nm+ light, the decoding algorithm in your camera still compensates for it. So if you dump the RAW file into DCRAW, what comes out still has something of a checkerboard pattern. Second, the false color effects generated by mid-band IR actually allow for more contrast control because there are multiple channels of useful information (and with 850nm+, you really need this, since everything likes to come out bright white in sunlight, especially around dusk). Eliminating this effect means that you have less ability to rebalance the tones in a scene.

None of this is to say that it’s good to meet one form of snobbery with another technical one. But let’s just keep the infrared world big, okay?

# # # # #

Advertisements

50mm f/1.5 Zeiss Sonnar (1937): first

20160106_191418

Above: Zeiss Jena 5cm f/1.5 Sonnar (prewar; 1937 example of the 1932 design) on a Leica M typ 240 with an Amedeo dedicated 50mm adapter. This particular lens is almost 80 years old.

1. The story

The derivation of the trade name “Sonnar”(which may have less to do with Sonne than being a portmanteau of Sontheim am Neckar) reminds one of the the way that the Mr. Sparkle is a joint venture of the Matsumura Fishworks and the Tamaribuchi Heavy Manufacturing Concern. Be this as it may, the Sonnar had but one goal in life: crush Leitz’s fast lenses in an era where ISO 12 film was the norm. And that it amply did. Even today, the performance of this uncoated lens is impressive.

When the Sonnar arrived in 1931 (f/2.0) and 1932 (f/1.5), the Tessar (or Elmar) was the gold standard in normal lenses: a well-corrected triplet that, in an era lacking anti-reflective coatings, sneaked in a little more correction by cementing two pieces of glass together. When it came time to exceed f/2.8, though, the real competition began:

  • In 1889, Paul Rudolph, working for Carl Zeiss, determined that the best balance of contrast, correction, and cost was a three-element lens called an anastigmat (trade name: Protar).
  • In 1895, Rudolph invented the Planar, which was a highly-corrected symmetrical lens. It was shelved soon thereafter, no doubt on account of the low contrast that occurs with many air-to-glass surfaces.
  • In 1902, Zeiss released the Tessar, which provided more correction than an anastigmat (by adding a fourth element glued to the the third) without increasing the number of air-glass surfaces. The Tessar was technically inferior to the Planar, but it did not have the two extra air-glass surfaces (each robbing 10% of the light, compounded).
  • In 1925, Max Berek modified the Leitz Elmax, which had a 1-1-3 (cemented) arrangement into the Elmar, which bore a heavy resemblance to the Tessar, allowing for a good 35mm-format lens with fewer elements and less assembly labor.

In parallel universe (but still orbiting around Zeiss)

  • In 1916, an American (Charles Minor) started adding elements to the triplet, but just in the front. The result was the Gundlach Anastigmat, which had a blazingly fast f/1.9 aperture. The contemporary ads show that this was actually a cine lens.

ultrastigmat
image credit: Central Camera 1936: Gundlach, Ultrastigmat, Bausch & Lomb, Verito Lenses; Packard via free images (license)

  • In 1922, Ludwig Berthele, working for Ernemann (of Ermanox fame) continued elaborating this into the Ernostar, which became on of the first plate lenses to hit f/1.8 (in 1924).

00QKTL-60433884

Scan used by permission of Peter Naylor.

  • In 1926, Zeiss bought Ernemann and acquired Berthele in the deal.
  • In 1931, Berthele made the first f/2 Sonnar, which was a new lens with an old name. It was for 35mm format and had a 1-3-2 arrangement, with the second and third group cemented together.
  • In 1932, he made the f/1.5 version, which added an extra element to the rear group.
  • In 1936, caught off-balance, Leica licensed the Xenon, a symmetrical Double-Gauss design from Schneider, licensed in turn from Taylor-Hobson in England (the Series 0), in turn had been cribbed from the 1896 Planar.
  • In 1944-1945, the Zeiss plants were bombed back to the stone age.
  • In 1949, the Xenon was updated with coagulation-style lens coatings and became the Summarit.
  • In 1950, the Zeiss-Option Sonnars came out with a new computations.

The circle was now complete: the entire high-speed lens space was dominated by Zeiss designs and would continue to be – for pretty much all time. When you stop and think about it, until the advent of things like the 50/1.4G Nikkor, the history of high-speed lenses had been nearly nine decades decades of Sonnar and Planar clones.

Why did the Sonnar do so well? It’s not so complicated. It all boiled down to the number of air-to-glass interfaces. The classic triplet (the anastigmat) represented the best balance between correction, contrast, and cost. But adding more elements (to get more correction) meant more air-glass interfaces. And that meant less contrast and more flare. Zeiss increased the correction by cementing additional elements together to make a total of three groups. Leica could not do this because it did not have the intellectual property rights to do so. During WWII, Zeiss dabbled in coating its super-speed lenses, but it was not even really necessary given the Sonnar’s high transmission.

2. Using one today

These days, the Contax rangefinder is almost dead, 35mm film photography has gone all “Tony-Bennett-in-the-late 1990s,” and so the only place you’ll likely be using one of these is on a Leica body. Fortunately, it’s pretty easy to do. You just need the appropriate adapter. These are not particularly expensive for APS-C (although they do incorporate focusing helicoids); they are more expensive for Leica cameras because they need a mechanism to translate the movement of a 52.3mm lens to a camera whose rangefinder mechanism wants a 51.6mm normal lens (how two German companies known for their precision could get so sloppy about what constituted a “50mm” lens is baffling – but being a big-name German optical company means never having to say you’re sorry….).

By far, the best adapters for Leicas are made by Amedeo Muscelli, and of those, the best is that dedicated adapter for Contax 50mm rangefinder to Leica M. This is  not the usual lens with the reproduction of a Contax helicoid and focusing scale; rather, combines with the lens to make a unit that looks a bit like an old Elmar (allowing, of course, for the streamlined – dare we say phallic) shape of a Sonnar. The dedicated adapter focuses in the same direction as a Leica, at almost the same rate of distance change per unit of turn, and it has a lever, which can be critical if you are using a collapsible Zeiss lens (since with a traditional adapter, you are grasping the lens barrel to focus – something you can’t do with a collapsible lens). When your lens is dialed in, this adapter focuses amazingly accurately right down to 0.6m – a lot closer than any Contax did.

And how do you dial one in? If your lens is front-focusing, the simple answer is to remove the lens cell from the Contax barrel and unscrew the rear group slightly. It is never more than 1/4 turn, and you can maintain the setting by wrapping the threads of the rear group in Teflon tape and screwing it back in. Back it out about a 1mm (circumferentially) at a time, and check the focus on near and far objects. Do note that where a Sonnar has a lot of focus shift, you’re going to have to choose whether to

  1. Have the lens front focus at f/1.5, reach focus at f/2.8-4 ,and hit focus at f/5.6 and smaller
  2. Have the lens focus dead-on at f/1.5, miss at f/2-4, and become usable again at f/5.6 and on.

3. Observations

The first observation is that finding a prewar f/1.5 Sonnar that is not totally trashed is not particularly easy. Fortunately, at least cleaning marks are not an issue on uncoated lenses unless someone used Soft Scrub as an optical cleaner. Which does happen from time to time.

The second is that in the central part of the frame, this lens is very, very sharp. It has decent performance at f/1.5 if you optimize for that aperture, loses precise focus from f/2.8-f/4, and comes roaring back at f/6.3. If you keep with the original collimation (or an approximation of it, you get really sharp pictures around f/2.4, getting better through f/8.

The third is that the coatings on postwar Sonnars are not moving the ball much in terms of performance. Because this was the last fast Sonnar I obtained, it’s easier to compare this to the 1961 Carl Zeiss version. The 1937 model performs similarly in most ways. It is very slightly softer, with contrast that is almost at the level of a 1977 Jupiter-3.

Flare is only slightly improved by coatings, and they do not resolve the “rainbow circle” flare that afflicts every Sonnars (even multicoated Sonnetars) when a point light source is just out-of-frame. The one unique failure mode is strong side lighting (from the looks of it between 75 and 90 degrees to the lens axis), which can cause a veil across the entire surface. This also happens to a lesser degree with postwar Sonnars and copies, just not quite to the same degree.

Overall performance is strikingly close to the postwar, if you allow for slightly improved spherical aberration on the older lens. The postwar version is a tiny bit sharper, but seems clear that this comes at the expense of bokeh, which goes from smooth disks to ringed disks. If you care about that stuff.

4. Roy Batty

The f/1.5 Sonnar was the proverbial candle that burned twice as bright, and by 1962 it was essentially extinct. The “twice as bright” part is doubly applicable to the 1960-1962 Car That it was so widely copied in the postwar era is puzzling. Granted, German patents were handed over to the Japanese, but in terms of sheer performance with coatings, there were already better lenses to copy (like the Xenon). Canon, Nikon, and Zunow all made their own versions. The Soviets made one too. Perhaps there was a “prestige” element to the Contax that was desirable to copy (though you would not have the all-important brand name). Or perhaps there was something about the mechanical design of a 3-group lens such that the cost of machining extra parts for 6 groups cost more than triple-cementing rwo groups. The world may never know. The fetishization of the Sonnar did not really get started until the mid-2000s and by then, it was based more on imperfection and “look” than a perception that it was actually better.

Conclusion

The prewar f/1.5 Sonnar is a worthy lens, though its relative scarcity does not exactly make it a value leader compared to postwar variants. As with any 50mm Sonnar, as long as you take care to control the placement of light sources, it can be another creative tool, if not a broader-use lens.