Author Topic: Need for Speed Redux  (Read 4969 times)

Birna Rørslett

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Re: Need for Speed Redux
« Reply #15 on: February 24, 2023, 13:39:17 »
The Oude Delft Rayxar 50/0.75 at its current "infinity" position [max. 75m due to the limitations of the adapter used] will render more distant scenes pleasantly blurred by its delicate bokeh. This night snowfall scene had strong wind, lots of snow in the air, so an overall blurring manifested itself anyway. Focus is on the Scots Pine in the foreground, distance about 60m.


paul hofseth

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Re: Need for Speed Redux
« Reply #16 on: February 25, 2023, 07:44:24 »
Ideal for decorating dinner plates

p.

Akira

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Re: Need for Speed Redux
« Reply #17 on: February 25, 2023, 11:11:45 »
I'm enjoying your crystal ball shots, Birna.   :)
"The eye is blind if the mind is absent." - Confucius

"Limitation is inspiration." - Akira

Birna Rørslett

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Re: Need for Speed Redux
« Reply #18 on: March 02, 2023, 16:20:30 »
The Mk.2 version of the infinity-focusing adapter is now completed. It indeed allows infinity focus also for the demanding Oude Delft 50mm f/0.75 Rayxar. Caveat: not [yet] on the Z30, because of the wide rear component of this lens. Or should I say, not until Erik the Great has had his hands on the Z30.... For the Rodenstock 50/0.75, the tiny Z30 does not complain too much and focus reaches to infinity as well.

The "X-ray" lenses completely dwarf the little Z30 :)



The fit is very tight, but by sheer serendipity the adapter fits. For more details, read on.

Birna Rørslett

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Re: Need for Speed Redux
« Reply #19 on: March 02, 2023, 16:35:16 »
Basically the new adapter is the old concept modified with my experiences from using said adapter extensively over the last weeks.

First and foremost, the adapter sits closer to the camera body. This was necessary to get infinity focus for the Oude Delft Rayxar 50/0.75, because the travel required exceeded what was possible in the threads of the mounting adapter. The adapter bayonet mount now is seated approx. 2mm  deeper.

Another important lesson from  the Mk.1 was the need for a more sturdy Z-mount. The lenses used are very heavy and are turned many many times by the fine threads on the adapter, thus excessive wear quickly developed on the cheap ultra-thin M42-Z adapters I normally use.

I solved all issues referred to above by using a 77-58 step ring as a mounting platform, This will accept a genuine factory Z mount, of which I still have a few left. The Z bayonet was force-fitted inside the 58mm threads by judicious use of a wood block and a hammer :). A few minutes worth of Dremelling on the outside of the step ring removed enough material to allow the 77-58 + Z mount to be -- again -- force-fitted into the big threaded mount for the lens. No glue or screws were used this time.

The final touch is making a small notch on the side so as to allow my finger tip to press the lens release button of the camera.

The Mk.2 "production time" was less than 1 hour as completing the adapter didn't involve pondering what bits and pieces to use.

Birna Rørslett

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Re: Need for Speed Redux
« Reply #20 on: March 02, 2023, 16:36:48 »
The adapter seen from the inside. The rim along the Z bayonet serves as a stop to prevent the mounted lens from going too deep inside the camera throat.

Birna Rørslett

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Re: Need for Speed Redux
« Reply #21 on: March 02, 2023, 16:58:03 »
Here is the Rodenstock 50/0.75 on the Z30. I just barely managed to keep the capture from being completely blown by overexposure :) A lens "speed" of f/0.75 in daytime puts demands on the resulting shutter speed.

Towards infinity focus the image circle with acceptable quality becomes smaller and this needs to be taken into consideration for objects at the periphery.

Erik Lund

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Re: Need for Speed Redux
« Reply #22 on: March 03, 2023, 09:40:07 »
Main point here is you succeeded to utilize the Nikon Z mount cameras for these old Speedy lenses, Very well done!
I too hope we find time to meet up, maybe in Norway or Netherlands  if there is anything I can help with I will gladly see what I can do!
Erik Lund

Birna Rørslett

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Re: Need for Speed Redux
« Reply #23 on: March 05, 2023, 12:58:20 »
A key to understanding these lenses, and how to use them for actual shooting, is to learn the actual image circle projected and its behaviour when focus varies. The image circle at infinity focus is approx. 23mm for the Rodenstock TV-Heligon 50/0.75, and at least 26mm for the Oude Delft Rayxar 50/0.75. The circle is smallest at infinity focus and will enlarge as the lens is focused closer. Concomitantly, field curvature, spherical aberration, and coma increases and eventually will be manifested also in the near centre of the frame.

In the typical X-ray application, two superfast lenses with apertures in the f/0.7-f/1.1 range were used either facing front to front or back to back. The usual close-focus loss of lens 'speed' was  avoided by the design, thus very weak X-ray images could be viewed on a TV monitor and/or recorded onto film. as shown below


From forum.mflenses.com

The TV-Heligon obviously was intended to transport the image onto TV. The initial record was through a corresponding XR-Heligon lens. The rôle of the Rayxar apparently is similar to that of the XR-Heligon, if I understood the [Italian] description at http://www.marcocavina.com/articoli_fotografici/Rodenstock_De_Oude_f_0,75/00_pag.htm . For our photographic applications, either system could be put to good use.

Another Norwegian, Espen Susort, describes his modification of the Rodenstock for Sony A7 cameras here: https://espensusort.no/2021/03/rodenstock-50mm-f-0-75-4/. I just became aware of his posts when my own adapters had reached the first prototype stage. Evidently, the additional 2mm of register distance of the Sony cameras created additional issues in the quest for infinity focus. His comments and the published test image for infinity focus clearly indicates he couldn't quite reach true infinity focus with his setup. He claimed best performance from 1.5 to 10m which is not consistent with my own observations. The lens indeed is at its sharpest for infinity focus, as it should be, and the performance graciously declines when the lens is focused closer. This behaviour is shared between the Rodenstock TV-Heligon and Oude Delft Rayxar lenses, and reflects the design criteria for their intended application as a component of a tandem relay system for X-ray machines.

Thus, the quality section of the projected image circle might be quite small, but with judicious framing of the subjects, we can make interesting images with most or all of what the lens projects. The aberrations increase very rapidly outside the core area, as evidenced below where I show the peripheral part of a Z9 frame done with the TV-Heligon. This was a blue-hour capture done well after the sun had set and thus the street lamps provided intense point-light sources.

Also note that even with the lens focused to a subject approx. 500m away, the depth of field still is inadequate to include much of the middle ground subjects. Consider the vintage of the lens and the effective speed of f/0.75, the lens really is amazingly sharp in the central parts of the frame. The designers needed 9 high-refractive elements in 6 groups to achieve such a performance, which obviously came at a considerable expense in its time.

golunvolo

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Re: Need for Speed Redux
« Reply #24 on: March 05, 2023, 13:21:13 »
Amazing way to visually explain image characteristics from the center to the edges. Outside the explanation, it gives me an impression of acceleration, of momentum and some deliberate haste.

  Thanks for sharing it!

John Geerts

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Re: Need for Speed Redux
« Reply #25 on: March 05, 2023, 17:04:07 »
Here is the Rodenstock 50/0.75 on the Z30.
Love this image.

Thanks for the explanations, Birna.

Birna Rørslett

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Re: Need for Speed Redux
« Reply #26 on: March 06, 2023, 09:21:55 »
One is *not* forced to shoot these 'X-ray' lenses at near infinity of course. Having a focusable adapter means it is far easier than before to get the precise framing one requires, whether at distance or in close-ups.

Protea by Rodenstock TV-Heligon 50/0.75 on the Z30. I slightly widened the internal port over the sensor to avoid the rear parts of the lens conflicting with the frame there. The lens now focuses perfectly to infinity also on this DX camera. Trimming was quickly done using a small scalpel :)

Birna Rørslett

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Re: Need for Speed Redux
« Reply #27 on: March 06, 2023, 14:13:11 »
At intermediate distances, the Heligon covers the DX format adequately, but the longer away the focused plane is, the smaller the image circle is. Still, if the Z30 is set to 1:1 format (16x16mm), one can fire away without too much concern about of black corners. Some smearing might occur, but it is easily absorbed in most scenes and of course, if the entire DX frame is in use, judicious cropping is always feasible to maximise the useful part of the frame. Sharpness in the centre part of the frame is amazingly good.

Birna Rørslett

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Re: Need for Speed Redux
« Reply #28 on: March 06, 2023, 14:25:25 »
Here is another example, with the Z30 again. Focus a little closer this time. The outcome is surprisingly sharp across the frame and the bokeh is smooth and silky.

MEPER

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Re: Need for Speed Redux
« Reply #29 on: March 06, 2023, 16:44:05 »
The "image signature" of the lens is slightly to the "blue side"?