How are lens coverage specs determined?

[Greg]

Good example are G-Clarons. Schneider publishes very conservative coverage figures. Personally use several G-Clarons easily beyond Schneider's published image circles.

I use a R D Gray 5.9 inch lens on my 11x14. Really only made to cover the 8x10 format with a sharp undistorted image, but because it more than illuminates my 11x14 inch negative, I am willing to accept its gradually degrading resolution in the corners. Most of my lenses have a few mm's sharpness cut off points but this lens has a gradual sharpness cut off point measured in inches.

Once bought a 183mm f/18 B&L Protar V. In my vintage B&J catalogue, it is listed under wide angle lenses for 11x14....
well mine just covers the matted final print's image of 10.5x13.5 inches but definitely not a full 11x14.

Guess the only real way to determine coverage is to test out the lens, but usually not possible at the time of purchasing the lens.

[Lachlan 717]

Once bought a 183mm f/18 B&L Protar V. In my vintage B&J catalogue, it is listed under wide angle lenses for 11x14....
well mine just covers the matted final print's image of 10.5x13.5 inches but definitely not a full 11x14.

At what aperture, Greg?

[Greg]

At what aperture, Greg?

f/64

[goamules]

Remember, you are comparing an 1880s lens with a 1930s lens, to today's photographic needs, in 2016. Each era was radically different. It's like comparing apples to oranges. In 1880, people rode horses, the transcontinental railroad or stage coaches were how you traveled long distances. Many people had fought in the Civil War. Photography was just developing for amateurs, and the terms were different. These Periscops were made during the wetplate era, into the dryplate era, over 130 years ago. The needs, technologies, and language were all different than today. You cannot read an 1880 lens catalog and expect the lens to meet your 2016 expectations. To me, that's part of the fun of trying lenses.

[Dan Fromm]

Garrett, the OP's Ser V Protar was first released in 1890 or so as the Ser V Anastigmat, was later renamed Protar. My 1901 Zeiss London catalog claims that the 182/18 covers 8x10 at f/36, 40 cm at small apertures. The OP may have misread his B&L catalog or the catalog may contain an error. Errors are very possible. My 1910 Zeiss catalog (in French) claims that the 185/18 will cover 80 cm at small apertures. This is impossible.

Greg, people here have two incompatible coverage concepts. Illuminates and puts good image in the corners. Your RD Gray lens passes the first for 11x14, flunks the second.

With lenses that don't have field stops (= sharp illumination cut off), the second concept is subject to interpretation. One photographer's "good enough" is another's "won't do". And one photographer's "stringent", it says, test shot is another's "are you out of your mind?" I'm tired of people using shots with detail only in the center of the field to show that the lens used covers the format well.

[Oren Grad]

Manufacturers' criteria for specifying coverage vary, depending on their respective optical standards and the uses for which a lens is marketed. These standards have changed over time, and sometimes the uses for which the lenses are marketed have changed too.

So yes, you need to judge for yourself. Sometimes you can rely on someone else's advice if you know their photography well enough to understand the standards that they apply, and how they relate to what you're trying to accomplish.

[Dan Fromm]

Hmm.

In the Apo-Ronar catalog, coverage = 2 x distance off-axis at which the 16 lp/mm f/22 MTF goes to near zero. Not clear what the magnification is.

In the Apo-Sironar-N, -S and -W catalogs, its where the 20 lp/mm f/22 MTF goes to near zero. Magnifications are 1:20 for the -N, 1:10 for -S and -W.

The cutoffs are a little variable for Apo-Grandagons and Grandagon Ns, but the same idea applies. Small f/22 20 lp/mm MTF sets the limit.

Coverage claims for some ancient designs have shrunk over time. My favorite example is Berthiot's Ser. VIa f/14 Perigraphes. 115 degrees claimed in 1912, 100 degrees claimed in 1950. As far as I know the design didn't change.

The same goes for Dagors. We've had some amusing brawls about their coverage.

[Drew Wiley]

G-Clarons evolved from process lenses, which were expected to hold crisp apochromatic dot pattern over the entire field of coverage. Therefore the published data was inherently conservative compared to what these lenses are capable of doing in general photography. The intended market for a particular lens series is always an important factor. But so is the overall company attitude. It's not just lenses. Even in machinery, I find the Germans to be very conservative in how they rate the performance of the products, and the Japanese, which are more relaxed. Here in the US, quite a few companies tend to outright lie about their products, which generally aren't made here anyway. But then you've always got exceptions, like VW diesels; but at least that was a very precisely engineered lie!