I'm a lens designer

[Teodor Oprean]

Ideas for a lens design exploration:

Lens 1: classic Tessar optimized for 4x5

focal length = 180 mm
maximum aperture = f/8
coatings = double-coating on every glass surface

By how much would double-coating increase light transmission compared to single coating?

Would such a lens compare foavourably with a 150 mm f/5.6 Apo-Sironar (N or S) in relation to the 4x5 inch film size?

Would the performance of this Tessar change significantly if one were to tweak the maximum aperture up or down from f/8 (e.g. further down by a third of a stop from f/8 to f/9)?

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Lens 2: Start with the existing Sironar-N 240mm f/5.6 mounted in the heavy and huge Copal 3 shutter and reduce the maximum aperture until the lens fits comfortably in a much more portable Copal 1 shutter.

What would be the maximum aperture for that lens?

What would be a good guess for the smaller filter thread?

Would the image circle be affected in any sense?


Teodor

[Lachlan 717]

My suggestion of a large IC 180-200mm has the benefit of multi-format. It's usable for the smaller ULF where the only options are the Grandagon/SA/SSXL, and also for those 8x10 and smaller shooters wanting to use huge movements (architecture et al.. Not a whole lot of choice in this sector if you include large IC.

[Mark Sawyer]

Before getting too carried away with the Hypergon, we should consider whether Jason (or anyone) could make such a lens. It's a simple enough looking formula, but the curves are extreme, and the glass very thin. Wisner promised a new Hypergon a while back, but never made one. Even Goerz had trouble making them. But it would be cool...

Another lens that might be worth considering is a fast modern Dialyt, similar to the Celor or Dogmar. Those were popular before WWII, even though as uncoated lenses, they suffered from quite a bit of flare. Many lf photographers are using modern coated Dialyt process lenses (Artar, Ronar, Process Nikkor...) for their excellent resolution and out-of-focus rendering, but those are all f/9 or f/10 lenses. I can't think of any modern (coated) fast Dialyts...

[Nodda Duma]

Before getting too carried away with the Hypergon, we should consider whether Jason (or anyone) could make such a lens. It's a simple enough looking formula, but the curves are extreme, and the glass very thin. Wisner promised a new Hypergon a while back, but never made one. Even Goerz had trouble making them. But it would be cool...

I'll ask the shop.

[Dan Fromm]

Dumb question: is the 110 degrees measured diagonally? Horizontally?

Diagonally. That's the convention.

However, many active posters here use other conventions, usually talk about the long edge. I disagree. If the lens doesn't cover the frame's diagonal it won't put good image in the corners.

Goerz claimed that the original Hypergon with fan covered 135 degrees with fan, 110 degrees without. An 20.5 mm 135 degree lens will just cover 100 mm, nominal 6x9's diagonal; not quite six stops down in the corners. See http://www.cameraeccentric.com/html/info/goerz_2.html

[Steven Tribe]

I don't think Goerz had too much problem in making them as the prices were very close to their other series.

The mount may be more difficult than the glass- see cross section.

[Old-N-Feeble]

Diagonally. That's the convention.

However, many active posters here use other conventions, usually talk about the long edge. I disagree. If the lens doesn't cover the frame's diagonal it won't put good image in the corners.

Goerz claimed that the original Hypergon with fan covered 135 degrees with fan, 110 degrees without. An 20.5 mm 135 degree lens will just cover 100 mm, nominal 6x9's diagonal; not quite six stops down in the corners. See http://www.cameraeccentric.com/html/info/goerz_2.html

Dan, I prefer to use the long edge of the film image to determine normal focal length but use the image diagonal to determine coverage needed. IMHO, "normal FL" and "minimal coverage needed" are not the same thing at all unless the image ratio is close to 1:1.25. I multiply the long edge by 1.25 to determine normal FL.

[David Karp]

David, such a lens already exists.
The Grandagon (non-N version) 115 is much smaller than the 120 Nikkor, covers 8x10 (barely) and comes in a Copal 1 shutter.
It is on the heavier side, like many Rodenstock lenses seem to be, but still at a manageable 550-ish grams.
Or did you mean something even smaller?

Took me a while to get back to this. As Ari and I discussed via PM, the 115mm Grandagons require those big 82mm filters to cover that large front element. The rear elements are big too. The Fujinons and Schneiders are similar. The 120mm Nikkor SW is 77mm. Something 67mm, preferably smaller if possible would be better for backpacking. Good 5x7 coverage with plenty of room for 4x5 (larger than the 120mm Angulon) is what I would love.

And the idea of a 4x5 triple convertible is intriguing. It would be great if it came with rear caps to protect each set of lens elements when removed from the shutter/barrel. It would also be cool if it came with an attachment, sort of like a filter step up ring, that could screw into the front of the shutter/barrel for easy attachment of filters when shooting with the rear element only.

Today I read the thread over on APUG. Fascinating.

[Dan Fromm]

Dan, I prefer to use the long edge of the film image to determine normal focal length but use the image diagonal to determine coverage needed. IMHO, "normal FL" and "minimal coverage needed" are not the same thing at all unless the image ratio is close to 1:1.25. I multiply the long edge by 1.25 to determine normal FL.

Fine, if you're speaking Feeblish. Most of us speak the common language.

[Old-N-Feeble]

Fine, if you're speaking Feeblish. Most of us speak the common language.

No need to be rude, Dan. I'm just expressing my opinion.