View Full Version : Please help with diffusion rings for Imagon 420mm

8-May-2012, 17:57
Time ago i have been helped by a very kind fellow member, with scans of the two missing "tea strainer" rings for my barrel Imagon 300mm.
I had in mind to copy them in black cardboard, but i gave up, waiting for metal caps that could me modified to imitate an original Rodenstock ring.
Recently i purchased a 420mm Imagon with NO rings, and if i can find 1:1 scans of the original rings, i think i will dedicate some of my spare time to the fabrication of metal rings, both for the 300mm and the 420mm one. There are metal caps that are available at shops specialized in wine production supplies. I hope to be able to modify them as replacement rings, but i still have to check if they store the right diameters :)
I hope to find an owner of a complete 420mm, who's willing to scan the rings, and email me the jpeg's. A barrel Imagon, without rings, is not very flexible, as there is no diaphragm, so i hope that somebody would help me.

Of course i am also willing to buy one or more original rings, if somebody has got them in some drawer...

A small side note:
the main reason behind my purchase was that the Imagon came with a large diaphragm lens holder, something that was probably missed by many Ebayers, because the holder was partly hidden behind the lens. What amazed me when i got the lens in my hands, was that the lens holder was different from all the others i own or i have seen in picture.
The holder has the conventional diaphragm leaves at the front, while at the back there are threaded clamps, solidal to the leaves, which allow to hold firm any large, heavy objective, even those that have the flange thread at the back end (and almost all the weight at the front). The kind of lenses which are, unlike the Petzvals, very difficult to be firmly blocked by a diaphragm lens holder.
Anybody out there owning the same kind of lens holder? Are they common, any more infos about them?

have fun


Brian C. Miller
8-May-2012, 21:36
Oh, lucky lucky lucky! There must be very few of those.

OK, what you need to do is do web search for "zone plate" and that will give you info on the diffusion "strainer" as they are termed around here.

The zone plate is used for "pinhole" cameras, where a more diffused, yet focused, image is desired. When the zone plate is made from metal, then it takes the form of the "strainer" found on the Fuji soft-focus 250mm and the Imagon. The size of the zone plate's concentric circles determines the amount of focus. In the case of the Fuji and Imagon, the innermost circle determines the f/stop.

Do you know what the lens' f/stop (h/stop for Imagon) is wide open? If you do, then you can calculate the rest of the f/stop sequence, since it is a ratio of opening to distance.

Back to the zone plate. What you do is you get some film with the clearest base you can find. Once upon a time we had Techpan and HIE/HIR. Very clear base on those. Then using a zone plate calculator, put in the numbers for the zone plate opening, follow the directions, and photograph the target, and develop the negative. I recommend that you cut out the center of the plate.

Alternately, you could try printing out the target (inverted, so the center is clear) on a sheet of transparency, and use that.

Now put the zone plate on the front of the lens, and you're done.

10-May-2012, 19:17
Thanks for the feedback.
I will consider making a "zone plate" with film, if i can't find a scan of the original "tea strainer" disks.
I hope to be able to find them, and copy the exact shape (with the chance to open and close the peripheral holes). Once you find an aluminium cap of the right diameter, i hope to be able to make a nice copy.
Unfortunately the 420mm can't be mounted in shutter, and without disks the control of both halation and exposure would be very complicate.

I am attaching two shots of the strange diaphragm lens holder, with the hinged sleds that help a lot in securing the lens in a firm way.
Sorry for the quality, it's just cell phone quality, without focus adjustment. Maybe you can't see very well, but i assure that the small "sleds" are threaded, which is good to avoid lens sliding.
The "T style" handle moves the blades, no provision for locking them, as far as i can see.
BTW, it's quite stiff, and it locks the Imagon 420mm in place without any problem. I guess that i must find a way to lock it, before cleaning. I am afraid that i would become too loose :)

have fun


Brian C. Miller
11-May-2012, 08:57
Well, there's a few things you can do for the shutter.

One is the Jim Galli shutter, where you take two darkslides and, forming a V with them, wave the gap in front of the lens.
Another is the home-made Guillotine shutter (there's an LF article around here about it), where a card with a gap is dropped in front of the lens.
And of course there is the Packard shutter (http://www.packardshutter.com/), which can be bought new.

11-May-2012, 10:06
I have a set of diffusion disks for the 420mm Imagon, and I can get 1:1 scans, photos, and dimensions to you. I'm not at my lens now, but I can get the scans in the next day or so.

11-May-2012, 20:57
Thanks. You're an angel!
You have just to do 1:1 scans with the holes in open position.
On monday i'll look for the caps. I hope i'll find a size which can be adapted.

About the shutter... i have no problems with it, i guess i have at home a complete set of external shutter paraphernalia :)
From Grundner to Sinar, and from Zettor to Plaubel. I have even remade the curtain for a Thornton Pickard, and purchased an old italian 4x5 studio camera (brand Lupa, aka Luigi Patui, Udine), just to cannibalize the nice connector for the pneumatic hose, which has a concentric knob, that operates the speeds of a big Silens shutter, via a small chain located on the back of the front standard. I dreamed about that simple mechanism for quite a long time, but normally you see it only on big wooden studio cameras, for which i have no place (one is more than enough:))
The real problem with a barrel Imagon with no disks is the diaphragm!
With 200/250/300mm ones you can fit the lens in a Compound shutter, and use its diaphragm to control both exposure and halation. With longer focals you don't have such possibility, and you are stuck with a lens which has only one aperture (wide open), and with LOT of softness, probably somewhat more than a 14" Kodak Portrait at full aperture, or maybe, even better example, like a sort of chromatically corrected Plasticca :)
I didn't test the lens as is, so i can't confirm, but i don't think i'm too far from reality.
With some kind of makeshift diffusion disks, the lens becomes more flexible, and definitely easier to use.

I repeat my appeal about the lens holder.
It's made in a very smart way, but i found no way to lock the leaves. I am sure i'm missing something...

have fun


12-May-2012, 12:36
The Imagon 420mm H5.8 lens has 3 diffusion disks, and all measure 98.0mm outside diameter (where it fits into the lens body).

On the H5.8-7.7 disk, the outer ring holes are 6.2mm, the inner ring holes are 8.2mm, and the single center hole is 46.0mm.

On the H7.7-9.5 disk, the outer ring holes are 5.2mm, the inner ring holes are 6.9mm, and the single center hole is 38.0mm.

On the H9.5-11.5 disk, the outer ring holes are 4.3mm, the inner ring holes are 5.7mm, and the single center hole is 31.0mm.

Good luck with your project, CJ.


12-May-2012, 14:36
Thanks, i am very grateful for your kindness, and for your very quick answer.

BTW, i am still interested in original diffusion disks on sale :)
Vintage LF lenses are also an object of affection for me, not just tools to make pictures, so i am always on the look for missing parts, accessories, and stuff like that...
I almost bite my tongue, when i found a post written on 2007, where the member "fix_se" was giving away for free a spare diffusion disk for Imagon 420mm!
At least i learned that there is always some hope :)

have fun


12-May-2012, 17:39
It's a universal lens holder. Comes up on ebay occasionally.

11-Jun-2015, 19:59
Thank you! me neither