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

[Marco Gilardetti]

So, after having long desired to own a portrait-specific lens, I could finally purchase the 250mm Rodenstock Imagon, in Compound 3 shutter. :D I would like to ask few questions to fellow photographers, in order to get nice images without too much costy and time consuming trial & error at first.

To begin with, this lens doesn't use the standard "f" values for aperture: everything is calibrated in "h". I'm not familiar with "h" and I would like to understand if, in practice, it is more or less the same, or how should I adjust the lightmeter. (Should anyone have a link to some theory behind "h" values, I would like to read the paper, thank you).

The second question is if this lens can also be used without any of the "scolapasta" diaphragms in front. I have seen pictures taken with them in which dot highlights are rendered as stars, and I don't really like these kind of cheesy effects. By the way, the hood is basically just a piece of tubing and I can hardly imagine that it wouldn't vignette the image at full aperture. Also, 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.

Third question: the Compound shutter comes with a magnificent, although uncalibrated, 17-something blades aperture diaphragm. Has anyone ever tried to use the Compound built-in diaphragm instead of the plug-in "scolapasta" accessories? Or is it placed in a wrong position for this type of lens, and won't work well? :confused:

Should anyone have any other kind of comment concerning the use of this lens, I'd be very glad to read. Thank you.

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[Bob Salomon]

Do a forum search I have answered these questions, and more, several times here.

[Marco Gilardetti]

It doesn't appear to be so, I'm afraid. A search with "Imagon" as keyword and "Bob Salomon" as author links to this sole thread, where you did not answer to any of these questions:

http://www.largeformatphotography.info/forum/showthread.php?36649-New-Rodenstock-web-site&highlight=imagon

[Jimi]

It's easier to do a specific search in this forum - for example this: http://www.largeformatphotography.info/forum/showthread.php?3716-How-to-focus-a-soft-focus-lens&highlight=Rodenstock+Imagon

[Emmanuel BIGLER]

Hello Marco !

The Rodenstock Imagon is a special lens as will be explained below.

H-numbers are the photometric equivalent of f-numbers for this lens when used with special diaphragms with a central hole and an array of smaller peripheral holes. Hence you should use the H-number exactly like the f-number of an ordinary lens for a proper determination of exposure with your favourite exposure meter.

The Imagon lens is a doublet, corrected for chromatic aberration but not completely for spherical aberration. When used as an ordinary lens with a central diaphragm, image sharpness somewhat increases when stopping down the lens until diffraction effects become the main source of fuzziness.

When used with the dedicated diaphragms, the Imagon actually records two images at the same time, a sharp image created by the central part of the diaphragm and a fuzzy image created by light rays crossing peripheral openings, those rays being strongly affected by spherical aberration.

Hence from an artistic point a view, the image is sharp, but each sharp image point is "surrounded" with a halo of fuzziness.

If you use the Imagon at full aperture without the special diaphragm, you get an image which is less interesting, it is simply, expressed in modern language, a poor image delivered by a poorly corrected lens ;)

Regarding the use of the built-in iris in the compound shutter, of course you can use it, you'll probably do not notice anything special due to the fact that the iris is located behind the lens elements and not in front, but again, without the special diaphragms, the behaviour of the Imagon might not be very interesting.

However, now that you have the lens in front of you, you should feel free to experiment and see which configuration suits you best.

Attached to this post id an example of image taken with the Imagon with a LF camera, photographer is Michel Guigue (France).

Out of focus images taken with an Imagon have a strange look, due to the fact that strongly defocused part of the image are created by the projection of the shapes in the diaphragm.

[Dan Fromm]

If you read French, Bernard Sulmon's report http://www.galerie-photo.com/soft-focus-objectif-portrait-flou.html should interest you. If you don't read French, the images should shed a little light anyway.

Emmanuel, I'm surprised you didn't suggest this article.

[Steven Tribe]

The english language catalogue is here.


http://www.cameraeccentric.com/html/info/rodenstock_1.html

Note that the coverage is not magnificent! Yours is OK for 4x5" - but the 360mm version is for 5x7".

[Jac@stafford.net]

Also, 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.

One of the discs in box should be an ND filter.

[Mark Sawyer]

Regarding the use of the built-in iris in the compound shutter, of course you can use it, you'll probably do not notice anything special due to the fact that the iris is located behind the lens elements and not in front, but again, without the special diaphragms, the behaviour of the Imagon might not be very interesting.

The iris on the Compound is in front of the lens, though closer than the h/stop discs. The h/stops give a different look called the "Imagon Effect". I prefer using the Compound shutter's conventional iris, which makes the Imagon similar to the Kodak Portrait Lens and other early achromatic meniscus lenses.

[Philippe Grunchec]

Heinrich Kühn says hello!

[plaubel]

Hello Marco !


- If you use the Imagon at full aperture without the special diaphragm, you get an image which is less interesting, it is simply, expressed in modern language, a poor image delivered by a poorly corrected lens ;)


- Out of focus images taken with an Imagon have a strange look, due to the fact that strongly defocused part of the image are created by the projection of the shapes in the diaphragm.


Hello, Emmanuelle,

that's my first time that I don' t agree with your statements.
Probably it's a matter of taste, but I love the Imagon wide open and without any disc.

Imagon 200mm, Xray, 5x7":
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Imagon 200mm, 4x5":

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This nearly gives the characteristically look of a meniskus, with all the lovely fuzz and glow.

The projection of the shapes from the original diaphragm has more to do with highlights and with "disc open" than with "out of focus".

Par example, for giving the picture a special flair it is necessary to bring the lens a bit out of focus, but it's mostly a matter of light to have or not to have this projections called "Kühn-bedbugs" in our country.
Mainly this bedbugs are hooking on highlights, so creating great glow with a lot of light and an opened aperture disc is difficult if not unpossible without this ugly projections.

Ritchie

[Peter De Smidt]

Hey Ritchie,

You're attachment links don't work for me.

Imagon no disk:
https://www.dropbox.com/s/253m7evmutkvyz8/Imagon_No_Disk.jpg?raw=1

Imagon, Middle disk, holes open:
https://www.dropbox.com/s/4ewadlrt0j634v9/Faux_Imagon_Middle_Disk_open.jpg?raw=1

Middle disk, holes closed:
https://www.dropbox.com/s/k1ml582d6uuowj3/Faux_Imagon_Middle_Disk_closed.jpg?raw=1

[plaubel]

Thanks, Peter, I hope this will work now:

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[Marco Gilardetti]

Thanks to anyone who participated in this thread with comments, images and documents (yes, I do read french!).

In my unity, the shutter and the diaphragm are both in front of the lenses as someone already pointed out. It's good to know that also the standard diaphragm can be used with no issues.

Although the Rodestock's user's manual also refers to a 4X neutral density filter, my unit came with a less useful yellow/green 2X filter. The set was possibly made before the user's manual was printed.

It is absolutely beyond my comprehension how can it be that the lens has a h=5.8 aperture, and then when the larger diaphragm is installed and part of the light is blocked, the aperture still stays at h=5.8. Can anyone comment on this, perhaps?

[Bob Salomon]

Thanks to anyone who participated in this thread with comments, images and documents (yes, I do read french!).

In my unity, the shutter and the diaphragm are both in front of the lenses as someone already pointed out. It's good to know that also the standard diaphragm can be used with no issues.

Although the Rodestock's user's manual also refers to a 4X neutral density filter, my unit came with a less useful yellow/green 2X filter. The set was possibly made before the user's manual was printed.

It is absolutely beyond my comprehension how can it be that the lens has a h=5.8 aperture, and then when the larger diaphragm is installed and part of the light is blocked, the aperture still stays at h=5.8. Can anyone comment on this, perhaps?
It remains at 5.8 when the largest disk is used with all of the periphery holes open. It is 7.7 when those holes are closed.

As the Imagon actually is two different focal lengths, one in the center of the lens and one at the edge of the lens you would defeat the purpose of the Imagon by using the shutter’s aperture ring as that would block the peripheral rays.

[Marco Gilardetti]

It remains at 5.8 when the largest disk is used with all of the periphery holes open.

OK. And how is this possible, from a physics standpoint, since part of the light reaching the front lens is being blocked?

[Peter De Smidt]

Got them this time, Plaubel. Thanks!

[Peter De Smidt]

This is using a Waterhouse-style stop in front of the lens, i.e. not using the official disks:

47mm opening:
https://www.dropbox.com/s/gaiwyc9winpkfc5/Faux_Ima_47mm_8bit.jpg?raw=1

57mm opening:
https://www.dropbox.com/s/91xe5azxmi854q9/Faux_Ima_57mm_8bit.jpg?raw=1

[Jac@stafford.net]

OK. And how is this possible, from a physics standpoint, since part of the light reaching the front lens is being blocked?

The ƒ stop (h stop) is given for the holes open with that sieve, not for the naked lens.

[Emmanuel BIGLER]

Hello all ! A nice discussion about the Imagon !!

Thanks to Mark Sawyer for correcting me regarding the placement of different elements in the Imagon.
The reason is: I have a shutter-less Imagon, and I remembered a diagram on a Rodenstock brochure (e.g. like the one on cameraeccentric's web site, I have another one in French) where the lens is presented with light entering from the right, unlike most conventional optical diagrams where light comes from the left. My mistake.

And thanks to Plaubel-Richtie for his comments which set the point on the question: do you like or not the special Imagon look? With or without perforated disk? I agree that the question is a matter of taste.

And thanks to Peter de Smidt for sharing the convincing pictures which demonstrate how the Imagon behaves.
In the series, I prefer sharper images, hence I prefer the ones with the perforated disk in place i.e. with the central part delivering an image somewhat corrected from spherical aberration and superimposed to a delicate "halo" of fuzziness.

However the when the shapes of this perforated disk are projected in out-of focus highlights, the visible shape is definitely non-natural and somewhat disturbing, I agree.

So with the Imagon, you should only take pictures of flat subjects with no depth, focused with the outer holes closed and then re-opened, if you want to see the added fuzziness but do not want to see the disturbing shapes in the background ;)

Not kidding, the out-of focus shape of a bright spot in Peter's image has a complex shape, as if there was another parasitic reflection added to what you would expect from the projection of the iris, looks like two projections of the iris with different magnifications?

[Emmanuel BIGLER]

And another idea regarding the h-number.

To me it could be defined like this:
#1 Take a picture of a gray card, properly focused, with the Imagon fitted with the special iris. Focus with the outer array of perforations closed, then re-open. Measure the illumination in the image plane.
#2 Substitute to the special iris a simple circular hole centered on the optical axis, located in front of the glass at the same place, do not re-focus in order to keep exactly the same distance between the glass and the image.

When both experiments yield the same illumination, the h-number in #1 experiment is equal to the regular f-number in #2.

[Peter De Smidt]

I dislike the funky aperture artifacts that appear on specular highlights in the background. I would avoid such highlights if I used the lens disk with the holes open. Note that using a regular iris in front of the lens would get rid of that behavior, and if you made the diameter of the disks smaller, you'd get sharper results, but with less of a glow. I prefer some sharpness + a glow, but that's subjective, of course.

[plaubel]

However the when the shapes of this perforated disk are projected in out-of focus highlights, the visible shape is definitely non-natural and somewhat disturbing, I agree.

So with the Imagon, you should only take pictures of flat subjects with no depth, focused with the outer holes closed and then re-opened, if you want to see the added fuzziness but do not want to see the disturbing shapes in the background ;)



Sorry, Emmanuel, but again I don't agree with the out-of focus-theme.
The main thing for creating disturbing shapes is direct light - of course in the out-of-focus-areas.
But it's not the out-of-focus area herself.
Again I read the manual of the Imagon, written by Michael Neumüller in his great book "the praxis of softfocus" from around 1950.
He describes " a special case is direct light, which requires closing the disk to avoid spreading highlights" (bedbucks).

He also describes the effect of increasing and decreasing the sharpness AND the glow by playing with the bellows distance but doesn't give a warning concerning spreading shapes in this situation.

I have learned to work with my Imagon exclusively from this book, so unfortunately I haven't more to say by own observations than this :-)


Concerning the iris of a shutter, let me throw in that Neumüller describes why it is best to put the iris in front of a meniscus (the Imagon is a kind of meniscus).

If the iris is behind the lens, this may give an effect which I can't translate exactly by word, but this may give problems at the edge between shadow and light.

I didn't use a meniscus with a shutter iris, but the resulting effect is described as a similary effect like burning a print in a bad way.

This effect seems to be more little, so I have problems to follow his examples given by pictures, but I want to spread the old news :-)

I didn't found the formula for the distance lens/front iris at this moment, but I remember nearly 10 percent of the focal length was given as the best distance.
I try to refind this formula.


Best,
Ritchie

[drew.saunders]

Cameraeccentric has two scans of old Imagon documents: http://www.cameraeccentric.com/html/info/imagon_1.html and http://www.cameraeccentric.com/html/info/imagon_2.html

Your shutter most likely needs to be serviced, or at least test it to see what speeds you actually get at each setting. Yes, you use the same H-stops value as F-stop when determining exposure, but if your shutter is a stop or more off, you're going to have problems. If you're not familiar with compound shutters, you can easily break one if you try to cock the shutter in "B" or "T" mode ("T" might be labeled "Z" on your shutter). Here's a video of the Imagon 300 in box, and Eddie shows you how NOT to break your shutter: https://youtu.be/AsL1ZNqUspM

I have a recent (post 1980 I guess) 250 Imagon in Copal shutter with all the disks and the 4-stop ND filter (more useful these days than the 2-stop green filter) and mostly use the 7.7/9.5 disk, at either setting. You'll get different results using the 5.8/7.7 disk at 7.7 than you will using the 7.7/9.5 at 7.7, so you'll want to experiment to see which one you like. As others have said, you're welcome to use the aperture either with or without the disks. I sometimes stop the aperture down w/o any disks to help focus, choose a disk, re-confirm focus, choose a disk setting, and then shoot.

[Marco Gilardetti]

Quick update.

I've had the shutter checked professionally and it worked absolutely perfectly. The technician said it was even a little bit faster than its nominal values (like 1/98th of second instead of 1/100). Not bad for a Compound of that age!

He also checked the f: value of the lens at full aperture and said it is 5,6. I have later grossly confirmed this value by comparison with another lens and a groundglass light meter. At the same time I have marked the standard apertures on the blank scale, and have later had the values engraved by a lady who engraves keyholders etc. with a pantograph (she did only a so-and-so work, but it's functional anyway).

With the help of a sir who owns a very big lathe, I managed to make the mounting flange. It was very interesting as I never used a lathe before, but man how much does it take to work with these machines! We spent the whole day at the lathe! Had I only knew, I wouldn't have asked him to do me this favour. In the end it turned out he didn't own the proper pair of gears to make the thread and we had to carry our piece to a friend of his who owned the appropriate gearing. Much more complicated than I thought, but interesting and stimulating nonetheless.

Finally, this weekend I took the lens out for shooting. I have had the hardest time of my life in focusing this lens. I could just inspect the developed film sheets so far, but it's obvious that some photographs are quite all right, while in others I managed to slip up the focus somehow. I bought a different loupe and will come back and repeat the wrong photographs as soon as possible.

[Bob Salomon]

Quick update.

I've had the shutter checked professionally and it worked absolutely perfectly. The technician said it was even a little bit faster than its nominal values (like 1/98th of second instead of 1/100). Not bad for a Compound of that age!

He also checked the f: value of the lens at full aperture and said it is 5,6. I have later grossly confirmed this value by comparison with another lens and a groundglass light meter. At the same time I have marked the standard apertures on the blank scale, and have later had the values engraved by a lady who engraves keyholders etc. with a pantograph (she did only a so-and-so work, but it's functional anyway).

With the help of a sir who owns a very big lathe, I managed to make the mounting flange. It was very interesting as I never used a lathe before, but man how much does it take to work with these machines! We spent the whole day at the lathe! Had I only knew, I wouldn't have asked him to do me this favour. In the end it turned out he didn't own the proper pair of gears to make the thread and we had to carry our piece to a friend of his who owned the appropriate gearing. Much more complicated than I thought, but interesting and stimulating nonetheless.

Finally, this weekend I took the lens out for shooting. I have had the hardest time of my life in focusing this lens. I could just inspect the developed film sheets so far, but it's obvious that some photographs are quite all right, while in others I managed to slip up the focus somehow. I bought a different loupe and will come back and repeat the wrong photographs as soon as possible.
1; the Imaginq changes sharpness with each change of the disk or the aperture ring.
2; the Imaginq does not have a point of exact focus at any aperture or distance.
3; wide open your lens is a 5.8, not a 5.6.
4; focusing must be done a shooting aperature, not wide open.
5; the shutter’s aperture ring should never be used as that will block off the peripheral rays which are the one# that create the Imaginq effect! Only use the disks. The small holes in the disks that surround the large center hole are there to allow the peripheral rays to hit the film or digital sensor.
6; the Imaginq requires a strong 5:1 lighting ratio from a strong light source, not an umbrella, to get the proper haloing.

[Armin Seeholzer]

I prefer using the Compound shutter's conventional iris, which makes the Imagon similar to the Kodak Portrait Lens and other early achromatic meniscus lenses.

Me to most of the time but in my case is it a Copal shutter! The lens without any Imagon discs in front its about f4,5 in my case if the Copal is also fully open! For the 250mm Imagon!
Mine 250mm covers 8x10 in near distances, but I do not recommend this for near Portraits!

[Daniel Unkefer]

Plaubel Makiflex 9x9cm SLR, 250mm Rodenstock H5.8 barrel mount lens, Legacy Mic-X dev, Foma 200

https://farm6.staticflickr.com/5513/30160624653_36f14ee418_b.jpg (https://flic.kr/p/MXc5VT)Makiflex Std 250 Imagon Foma 200 2 (https://flic.kr/p/MXc5VT) by Nokton48 (https://www.flickr.com/photos/18134483@N04/), on Flickr

https://farm6.staticflickr.com/5723/30717824571_cf9d978110_b.jpg (https://flic.kr/p/NNqT42)250 Imagon Makiflex Foma (https://flic.kr/p/NNqT42) by Nokton48 (https://www.flickr.com/photos/18134483@N04/), on Flickr




200mm Rodenstock Imagon barrel mounted, on Plaubel Makiflex board;

https://farm6.staticflickr.com/5536/14456392478_88081464fd_c.jpg (https://flic.kr/p/o2sMQb)001 (https://flic.kr/p/o2sMQb) by Nokton48 (https://www.flickr.com/photos/18134483@N04/), on Flickr




300mm barrel mounted Rodenstock Imagon mounted on Plaubel Makiflex lens board. I have owned Imagons from 120mm to 420, all are in barrel mounts (no shutters). This unit is cumbersome, but NOT heavy. Works well. The screw together tubes come from China.

https://farm6.staticflickr.com/5565/15041440930_311fba3115_c.jpg (https://flic.kr/p/oVajms)001 (https://flic.kr/p/oVajms) by Nokton48 (https://www.flickr.com/photos/18134483@N04/), on Flickr

[Daniel Unkefer]

My 120mm and 150 Imagons I sold to "Mr. Pentacon Six". I had a special Rodenstock helical custom modified to fit my P6 and EX66 cameras.

See his extensive article on these unique lenses here:

http://www.pentaconsix.com/imagon.htm

[Marco Gilardetti]

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.

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[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.

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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.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.