Need for Speed Redux

[Birna Rørslett]

More than two decades ago, in my former existence, I  wrote an article entitled 'Need for Speed' on the ancient naturfotograf.com website. This piqued the interest of many people to use, or more precisely, abuse - old optics used on X-ray machines and similar. Brand names such as Rodenstock TV-Heligon or De Oude Delft Rayxar became familiar to a wider circle of enthusiasts. And prices on eBay soared accordingly.

There industrial lenses had a common factor, viz. rather unheard of "speed" with exotic apertures of f/0.7, 0.75, 0.8, ... Real speed monsters they were? Or no, as the nominal f-number figure N of a lens refers to infinity focus. However, these lenses all had huge font size and a tiny rear element, leading to a small pupil factor P

 P=[size of exit pupil]/[size of entrance pupil])           

again leading to larger f-numbers N' when the lens is focused closer to give magnification m

  N' = N*(1 + m/P)

Now, in their designated position, the "X-Ray" lenses were used as a tandem pair with each lens at infinity focus, so the attained "speed" really was awesome and the f/0.75 etc. manifested.

The Rodenstock TV-Heligon 50mm f/0.75, a widely used lens in its time, quickly was pooed upon as yielding very soft and low contrast images of a blurred nature. As this deviant rendition was its raison d'etre for photographers seeking an alternative to the increasingly perfect rendition of modern optics, the hard-core experimenters soldiered on with their adapted glass heavyweights for years, until the speed craze petered slowly out.

Now, if image quality was abysmal, why were those lenses used in the first place? Obviously the photographers abused the optics in a non-designated manner, and because infinity focus could not be reached, never observed the potential quality of the Rodenstocks or Rayxars.

The SLR or DSLR principle of former days lead to a long back focal distance, ie. the distance from the lens mounting flange to the film or sensor. With the arrival of mirrorless cameras, the potential of mounting lenses closer to the recording surface became a reality. Still, the sheer physical size of the "X-Ray"  optics was an obstacle not easy to overcome.

Enter the Sony E-mount (register 18mm) and Nikon Z (register 16mm). In particular the Z system, with its very wide throat, opened up a new avenue of possibilities. Even more so the arrival of the shutterless Nikon Z9!! As the back distance for infinity focus for such optics are generally < 10mm, some even as short as 3-4mm, not having a shutter in conflict with the rear part of the lens is a big bonus. So when I got my Z9, plans for adapting my exotic lenses immediately were drawn up. Real life then bit back with a nasty Covid-19 infection thus we need to fast forward approx. 1 year to see the idea in fruition.

Here is a demonstration of the inherent quality of the Rodenstock TV-Heligon at a focused distance of approx. 100m. Consider this was at an effective aperture f/0.75, the quality is really surprisingly good for a lens more than 50 years old !! This is on the Z9. Right-click to open the image in a separate tab to reach 100%.

Read on to learn how this feat was achieved.

[Birna Rørslett]

To satisfy readers' curiosity, here is a quick run-down on how I adapted my Rodenstock (or Rayxar) to infinity focus. Both lenses use the same adapter

First, the parts. The lens (Rayxar 50/0.75), the mounting flange for the lens (approx. 80mm thread inside), a 52-77 step ring, and a flat and ultra-thin M42-Z adapter. I got the mounting gear as part of the lenses at the time of purchase.

[Birna Rørslett]

The step ring sits inside, with some trimming.

[Birna Rørslett]

Using my Dremel, the step ring is trimmed to be flat, ready for the Z mount. I secured the M42-Z adapter with a counter-thread slim plate on the inside (poked out from a full-size M42-Z adapter by Pixco if memory serves). This last precaution is not really necessary as the oven-cured epoxy glue will hold the mount in place, but one can never be safe enough I presume?

That's all there is to the adaptation. Focusing to infinity now is a breeze. The full "speed" f/0.75 is manifested.

[Birna Rørslett]

And finally, the adapted Rodenstock 50mm f/0.75 lens on my Nikon Z9, seen against Tatiana's beautiful handcrafted runner. I have made a make-shift lens hood for the lens as well, however aim to have it replaced by a properly fitted 86mm hood once the ordered parts arrive.

[Erik Lund]

Thank you for sharing your Speed Solution for Z mount! The results speaks for themselves - Marvelous 

[Birna Rørslett]

Thanks to you as well, Master Erik. I have silently watched your deft workmanship up close so many times that some of the experiences have rubbed off

At present I seriously consider getting a low-end camera like the Nikon Z30 and have it modified for use with the X-ray lenses. It would need internal changes to allow the rear part of these lenses to be seated close enough to the sensor surface. A cover frame around the sensor will block access. Once this is trimmed off, the lens should work effortlessly even on this camera. There is a shutter curtain on the Z30, but that ought not to cause problems as the Rodenstock etc. works well on the Z6/7 bodies, the latter also having shutter curtains.

With the Z/DX, nearly all of the sensor surface may be used. However, the overhang of the finder of my Z fc prevents the chosen adapter from being mounted. Hence the idea of using the modest Z30 for my X-Ray optics.

Maybe a spring visit to Copenhagen would be possible?

[John Geerts]

Great article Birna. And thanks for showing the adapter.

[Birna Rørslett]

I was lucky that I kept the mounting brackets accompanying these lenses at the time of purchase. They typically were offered on eBay etc. as spare parts or lab surplus, and sometimes rather comprehensive mounts followed with the lens. No idea of the present situation, but I presume it cannot be too difficult to find similar parts even today.

I will use a second mounting flange for a bespoke adapter for the Rayxar, as this lens needs to be seated a tad closer than the Rodenstock. I also have a Kowa 55mm f/0.8 that might require a short back focus distance (using the same thread).

An infinity focusing adapter for the Rodenstock 100mm f/1.6 was made several years ago, when I got my first Z camera. This lens is very easy to adapt as the rear focal distance is much longer, around 35mm if memory serves.  The projected image circle of the 100/1.6 covers the FX format but one should cut down a few mm in the extreme corners for infinity shots, as they may be a little soft. That lens is superb for IR photography as well.

[Fons Baerken]

Great and successful project!

[golunvolo]

Looks amazing and ready for fun.

[paul hofseth]

Impressive result, both mechanically and technical pictorial quality.

When I first encountered such a thick monster I was impressed by its f-number and at its  ca 10USD price, it could not be left behind.

p.

[Birna Rørslett]

I have read up on the more technical descriptions of these lenses, and the differences noted earlier are confirmed. According to this informative Italian web site

http://www.marcocavina.com/articoli_fotografici/Rodenstock_De_Oude_f_0,75/00_pag.htm

the back focus for the TV-Heligon 50/0.75 is 6.1mm. Thus, no wonder my adapter allows infinity focus -- and beyond -- for the Heligon, as it can seat the lens down to approx 3mm away from the sensor surface. I can easily observe the treeline on the horizon coming into focus when I focus "closer".

For the Oude Delft 50mm f/0.75 Rayxar, the back focus is given as 0.8mm. My current adapter cannot produce this short distance so "infinity" at present is approx. 75m with the Rayxar. An example is provided below. The image quality if anything is even better than for the TV-Heligon, however the danger of scratching the sensor surface is so high I now think that say a cheaper Z30 should host this lens instead of the Z9.

Anyway, the evidence that the Rayxar can deliver very fine quality at distance,

[Birna Rørslett]

Rodenstock TV-Heligon 50mm f/0.75 can now easily do infinity focus. The hill side on the opposite side of "my" river valley is approx. 5km away and serves as my test object. I needed in fact to focus closer in order to get the hillside into focus.

Centre of frame on Z9, 100%. Exposure dropped perilously close to the 1/32000 sec limit of the Z9 thus I had to dial in a negative EV correction to handle the situation. The "X-ray" class of f/0.75 lenses are ill suited for photography in bright sunshine, unless one adds a dense filter

[Birna Rørslett]

Action photography by the Rodenstock TV-Heligon early this morning. The ultrafast lens helped give barely adequate shutter speed



The lens in its current adapter has "unit" focusing, and as the thread pitch is fine, manual focusing is pretty slow. Still doable and this opens new avenues to explore.