Imagon - underneath covers

[jjstafford]

Looking at pictures of an Imagon and it is merely a rear element, inherently very soft, fuzzy, all the Bad Stuff. It achieves recognizable images only through the variation of disks put in front of it to make variable soft focus.

What is the rear lens? Could it be an element cluster found on another of
rodenstock's 'normal' performance lenses, or possibly in many other lenses?

I'm wondering if we might find a sleeper here.

jj

[David A. Goldfarb]

It's a very old design. I don't think they are just using a cell from another lens, though you can get a soft look that way with some lenses.

Personally I don't like the Imagon look as compared to other soft focus lenses. Too mushy for my taste.

[JG Motamedi]

The Imagon is a meniscus, one of the simplest lenses; a cemented doublet. Daguerre's first camera used one of these, and it was the only lens available until the invention of the Petzval in 1840. The earliest "landscape" lenses were all this design, with a small stop in front. I attached an photo of an early (1855) landscape lens (can't remember the source, sorry...). These were not terribly sharp lenses, but they functioned as was needed.

The Kodak Portrait is also the same design, as are many early soft focus lenses. As far as I know, there are no modern LF lenses which incorporate a meniscus, although it would be easy enough to buy one (unmounted) from a optics firm or as surplus. Alternatively, the front element of a Petzval or either of the elements of a Rapid Rectilinear (or Verito) are meniscus lenses. Most Petzvals were designed so the front element could be swapped with the rear and used for "views".



This is the official Rodenstock schematic (although I think it has been discontinued) from http://www.prograf.ru/rodenstock/largeformat_en.html. Note the doublet on the left and the disc (aperture) on the right.

[Donald Qualls]

Most refractive telescope (and binocular, and monocular) objectives are a cemented doublet with an overall meniscus form. To use them like the meniscus lenses in photography, you'd mount them backward (i.e. concave to the scene) and put a stop in front (though I don't know how to deteremine how far in front). You can often pick up surplus small objectives for very low prices -- if nothing else, keep an eye open for the junky, almost worthless telescopes sold for kids to show up at second hand stores with most of the accessories missing. These will typically be between 40 and 60 mm diameter, and have a focal length of anywhere from 12" to 36"; they're mounted in plastic and can be removed without too much trouble. The same glass from a monocular might be as little as 20 mm diameter and have a focal length as short as 8". The glass itself is usually halfway decent even in the cheapest telescopes (they just buy half a million lenses at bulk and cheat on the mounts, eyepieces, tripod, etc.), especially the older ones from before about 1980.

[Ole]

Or a good-quality close-up lens? An achromatic +2 close-up should be a 500mm lens of "photographic" quality - and you can buy one with the treads for a shutter!

[Seele]

I think the Imagon was originally a Staeble design before it merged with Rodenstock.

The cemented positive in the Imagon was not designed like most "single combination" lenses of the past, such as the Lerebours et Secretin as illustrated; those earlier lenses were trying to achieve as much correction as possible, but for the Imagon, it was designed to have under-corrected spherical aberration.

I have an example of an American lens of the same type, the "Port-Land" by Spencer of Buffalo, NY, and of course without the sink-strainer. the result is that the "core" image merged with the "halo" image, making focussing pretty much impossible. Stopping it down to focus is also tough, because it also gets focus shift too. The whole idea of the sinkstrainer is to retain a bright core image and then a series of darker, overlapping halo images.

Some time ago I started a thread on how to make duplicate sinkstrainers for the Port-Land and I don't seem to have any answer. If anyone has an Imagon, I would sure like to hear from him/her so as to get those dimensions!