Retrofocus LF Lenses - Wide Angle One-Shot Cameras (Tri-Colour/Three-Color)

[holmbāgu]

Hi all, just found and posted on this thread, but wanted to create a new thread altogether.

Retrofocus lens designs have never really been needed on large format cameras, though there is at least one excpetion; the one-shot camera.

I'm wondering if the Curtis Color Stellar 133mm f/5.3 (4x5") is the only one of this type ever made(?) http://www.vintagephoto.tv/scouts2.shtml

A project to build a one-shot camera is currently in its infancy over at APUG (really just the "dreaming" stages), but I thought I'd go ahead and solicit information regarding lenses of this types.

Due to the lengthy light path necessitated by two mirrors, a retrofocus design is needed to achieve any semblance of a wide-angle view on a camera like this.

Also, it doesn't have to be confined to LF either; MF and even 35mm would be interesting to know about too. Basically any lens with a wide-angle of view relative to it's focal distance would be great to learn about.

Thanks!

[holmbāgu]

update: http://tech.groups.yahoo.com/group/h...phy/message/26

Indeed, Scott, owner of that website, believes it might be the only one of its kind.

[Drew Wiley]

Have you thought about using a beam-splitter prism rather than pellicle mirrors? This would
add weight and expense, and require much more accurate placement and machining, but
would also hypothetically work a lot better than the old traditional designs like the Curtis
or Devin, esp with wide-angle lenses.

[Dan Fromm]

Drew, brother Holmburger has been fantasizing about trichromy and one-shot color cameras for quite a while now. Y'r suggestion doesn't solve his problem, which is finding a wide angle lens that covers the format(s) that fascinate him and has long enough back focus to focus to infinity in front of all those beamsplitters.

But y'r suggestion put me in mind of something else. I have a couple of service manuals for Canon Super 8 cameras that show their lenses in some detail. There's a beamsplitter in the light path to bleed off light and image for the viewfinder and many curved bits of glass between it and the film plane and between it and the finder eyepiece. I don't have a Bolex H reflex manual, but that camera has to have a similar arrangement. If the squeals of frustration from the characters who put cine camera lenses on tiny chip digicams are to be believed, none of the short lenses for H reflexes is retrofocus. So there's a hint. Relay lenses.

In addition, a number of supplementary wide angle lenses that screw into the front of cine and video cameras' "prime" lenses have been offered. I've got good footage in air and in water with one dedicated to my Nautica and in air with one dedicated to my 314XLs. So-so results with one made for Canon 814XLS/1014XLS on my Beaulieus' 6-66/1.8 and 6-70/1.4 Schneider zooms; vignetting due, I think, to the fact that the lenses' front elements are set well back in their barrels. EKCo made a converter for the 25/1.4 Cine Ektar II that shortens it to 15 mm. I have a couple of them, they work well. There's another hint for the seeker after color from black and white. Afocal wide angle attachment.

[Kerry L. Thalmann]

I believe the Komura Super Wide lenses (75mm f6.3 and 90mm f6.3) made back in the 1970s were retrofocus designs. They definitely cover 4x5 and I seem to recall the 75mm had a ftf at infinity of around 100mm. I don't recall if they made any other focal lengths.

I have no idea if these would be suitable for your application, and that's all just off the top of my head, but should give you something to start googling.

Kerry

[Paul Ewins]

I've got both the 75 and the 90 Komura. At infinity the rear of the 75 is about 58mm from the GG and the rear of the shutter is around 100mm. The rear of the 90mm is 75mm from the GG and the rear of the shutter is around 135mm from the GG. (That is a very rough measurement).

[Drew Wiley]

Anything can be done for a price. The prism can have each surface coated separately
eliminating the need for separation filters near the film plane. You could even have optical
elements incorporated onto the prism itself. All hypothetical, though I know people who
could do it. Even custom lenses could be had and at serious quality. I've thought about
this topic myself for awhile. I just don't have the kind of budget that NASA or ATF or NSA
has. But it would be nice to own something better than a tricolor Holga (you could duct
tape three together)!

[ic-racer]

I like the idea. B&W film will likely be around a long time and can even be made at home.

If I were to make a modern 3-way camera from scratch I'd look into a compact 3-way prism (rather than mirrors) to fit behind a non-retrofocus lens. I'd use rollfilm and have the 3 images right next to each other on the roll, or have them one-frame apart with an interleave.

[Leigh]

...I'd look into a compact 3-way prism...

That's quite neat. Is it a commercial product or a special?

- Leigh

[Emmanuel BIGLER]

Hello from France

If you are interested in tri-colour cameras with beam-splitters you can have a look at Henri Gaud's blog. Henri Gaud is a French professional photographer who does a lot of tri-colour photography with regular cameras but also with one-shot pre-WW-II beam-splitter cameras.

He has gathered information about tri-colour cameras, read here
http://trichromie.free.fr/trichromie...php?q=one+shot

And he has resurrected several one-shot tri-colour cameras, including:
A Curtis for the 2x3" format
http://trichromie.free.fr/trichromie/index.php?q=curtis

A Hauver for the 5x7" format
http://trichromie.free.fr/trichromie/index.php?q=hauver

The Hauver in action last spring (May 2011) at one of our informal LF meetings

Didier Chatellard from La Chaux de Fonds, Switzerland has bult a prototype 4x5 tri-colour camera
but I do not know if the camera actually works: my understanding is that the very hard technical point is to find pellicle beam splitters that would not cost you an arm and leg.
You can contact Didier Chatellard through his web site dedicated to lightweight wooden 4x5" cameras that he fabricates.
http://www.obscura-camera.com/spip/spip.php?rubrique4
http://www.obscura-camera.com