Rodenstock Imagon Tiefenbildner 250mm h=5.8, some questions.

[Bob Salomon]

With some deep web search I could finally come up with a picture of a 250mm Imagon with what looks as a factory-engraved aperture dial. Full aperture on Compound 3 shutter reads f:5,5. That's reassuringly close to what I have measured (f:5,6). Although the picture is taken in perspective, there are anough reference details on the shutter body in order to add (or verify) the other aperture markings, should anyone want to add a full aperture scale to its Imagon 250mm in Compund 3.

Attachment 173607

Since you should never use the aperture in the shutter for an Imaginq the Imaginq shutters never come with marked scales. As using the aperture in the shutter blocks off the important peripheral rays needed for the Imaginq effect!
This picture is either of an Imagon in a remounted, non factory supplied shutter or someone paid to have the scale made. Especially as the the wide open Imagon is 5.8 not 5.6 or 5.5. Further the markings do not match the disk values either. The best advice for best results with an Imagon is to open the shutter all the way and tape or glue the ring to keep it there.

[Marco Gilardetti]

Bob, I don't get why you take this thing with such religious orthodoxy. This is possibly the third time that you repeat these same things, constantly contradicted by evidence. The whole world used the Imagon also without the discs, there are pictures taken without them even posted in this thread, for my 2 cents I also took pictures without them in the past weeks and they came out just wonderfully. The Imagon user's manual itself invites to experiment without the discs. In my opinion, there is evidence enough that yes, it can be used without the discs.

As a physicist, I don't get your note about full aperture being 5,8 either. That's the aperture when the largest disc is in place. The larger disc blocks out a considerable amount of light. If the light blocking is removed by removing the disc, more light will pass and the figure will no longer be 5,8. Then how much will it be? By measure, as it is perfectly logical, it appears to be increased between 5,6 and 5,5 on a Compound 3. I think it's pretty straightforward to the point that I cannot devise any possible contradiction in the argument. Can you please expand why you insist in writing that it is not so?

[Bob Salomon]

Bob, I don't get why you take this thing with such religious orthodoxy. This is possibly the third time that you repeat these same things, constantly contradicted by evidence. The whole world used the Imagon also without the discs, there are pictures taken without them even posted in this thread, for my 2 cents I also took pictures without them in the past weeks and they came out just wonderfully. The Imagon user's manual itself invites to experiment without the discs. In my opinion, there is evidence enough that yes, it can be used without the discs.

As a physicist, I don't get your note about full aperture being 5,8 either. That's the aperture when the largest disc is in place. The larger disc blocks out a considerable amount of light. If the light blocking is removed by removing the disc, more light will pass and the figure will no longer be 5,8. Then how much will it be? By measure, as it is perfectly logical, it appears to be increased between 5,6 and 5,5 on a Compound 3. I think it's pretty straightforward to the point that I cannot devise any possible contradiction in the argument. Can you please expand why you insist in writing that it is not so?

Marco, I was the product manager in the USA for Rodenstock from 1986 to 2015. The 200, 250 and 300mm Imagon lenses are all 5.8 without a disk and 5.8 with the disk with the largest center hole with all periphery holes open. These are H stops, not F stops.

The Imagon is actually two different focal lengths. The center of the lens is a different focal length then the periphery. The more of the surrounding holes are open the more of the surrounding focal length effects the image and creates the chacteristic Imagon effect. By using the aperture in the shutter you block off this characteristic Imagon effect.
The Imagon also behaves differently in other ways. It has more DOF then a regular lens of the same focal length and equivalent speed. It wants a much stronger lighting ratio then other lenses. It has no point of truly sharp focus and changes focus with each different H stop, etc. it wants a strong elliptical main light, not an umbrella for its best effect.
Granted there are people who prefer to use the lens differently. But to Master the Imagon one needs to master how it was designed to be used first.
In the instruction pamphlet there is a set of images of a glass shot at each H stop to show the effects possible. None are done by using the aperture in the shutter. Nor does a barrel mount, NF, mount for an Imagon have a diaphragm.

[Marco Gilardetti]

Dear Bob, I appreciate your experience at Rodenstock USA, as well as your commitment on this forum, believe me. However, the law of physics cannot be overridden and there is no way that while blocking some light with a metal sheet the overall light passing through would be the same. This is, simply put, plain impossible. Should anyone be able to do that, he would win a Nobel prize instantly.

There is also no way that a spheric lens may have two distinct focal lengths. It will have *infinite* focal lengths from center to periphery, each differing infinitesimally by all others within a continuum range. It also cannot have more depth of field than any other doublet of the same type, quite obviously, and behaves just as any other doublet of the same type, obviously again.

The so-called "increased depth of field" affirmed in Rodenstock's documents is due to the fact that the perforated discs intercept the rays at two different radiuses; those will form approximately two (more or less) distinct images corresponding to approximately two focal lenghts (however, it has to be noted once again that the focal lenghts involved are still infinite and continuum around two ranges). This is why details that are not on the same plane may appear approximately in focus on the negative. As a side note, this interesting effect is achieved by blocking off part of the light, at the expense of a decreased f: number when the discs are in place. As always happens in physics, you loose some, you gain some (if it wasn't so, Nobel prize etc.).

By omitting the use of the discs, the photographer gives up this feature and works with *all* the (inifinite) focal lengths set. Not only the diffusion effect will not be quenched, but it actually gets more prominent. The character of the image will of course be different - not necessarily better, not necessarily worse - the Imagon just turns into a different tool.

[Bob Salomon]

Dear Bob, I appreciate your experience at Rodenstock USA, as well as your commitment on this forum, believe me. However, the law of physics cannot be overridden and there is no way that while blocking some light with a metal sheet the overall light passing through would be the same. This is, simply put, plain impossible. Should anyone be able to do that, he would win a Nobel prize instantly.

There is also no way that a spheric lens may have two distinct focal lengths. It will have *infinite* focal lengths from center to periphery, each differing infinitesimally by all others within a continuum range. It also cannot have more depth of field than any other doublet of the same type, quite obviously, and behaves just as any other doublet of the same type, obviously again.

The so-called "increased depth of field" affirmed in Rodenstock's documents is due to the fact that the perforated discs intercept the rays at two different radiuses; those will form approximately two (more or less) distinct images corresponding to approximately two focal lenghts (however, it has to be noted once again that the focal lenghts involved are still infinite and continuum around two ranges). This is why details that are not on the same plane may appear approximately in focus on the negative. As a side note, this interesting effect is achieved by blocking off part of the light, at the expense of a decreased f: number when the discs are in place. As always happens in physics, you loose some, you gain some (if it wasn't so, Nobel prize etc.).

By omitting the use of the discs, the photographer gives up this feature and works with *all* the (inifinite) focal lengths set. Not only the diffusion effect will not be quenched, but it actually gets more prominent. The character of the image will of course be different - not necessarily better, not necessarily worse - the Imagon just turns into a different tool.

Enjoy your lens and your life.

[Daniel Unkefer]

has anyone ever tried to use the Imagon with neutral grey filters to control light, perhaps? I ask because the maximum speed of the shutter is insufficient to deal with sunday light at full aperture.Attachment 170471

I have Imagons (in barrel mount; no shutters) in focal lengths of 120mm, 150mm, 200mm, 250mm, 300mm, 360mm, and 420mm.
I quite often use the supplementary filters (ND or YG) to reduce the light levels to the film, for precisely the reasons you mention. I believe that is why Rodenstock supplied the filters. And also films were not as fast as today, when these lenses were most popular (up to 1950s/1960s) The H5.8 Imagon disk provides the maximum "Imagon effect" as you know, and that is what I prefer. I have never used my Imagons without the Imagon disks. But I guess try it as a test and see what happens. If you like it you like it.