Lens coverage by design?

[domaz]

Is it generally possible to calculate a lenses coverage by knowing it's design and focal length? Obviously individual copies of lenses are going to vary somewhat, but on a general basis is it possible to say- this lens is a Plasmat so it's going to cover XX degrees, this is a Tessar so it will cover Y degrees? If so does anyone have a list of lens coverages by design?

I'm hoping to add a lens coverage calculator to the (free) LF Android App I'm developing.

[E. von Hoegh]

You could probably arrive at an approximate minimum coverage. Once you define "coverage", that is.:)

[Oren Grad]

No. Too much design variation under the general types designated by those names.

[GPS]

No. Too much design variation under the general types designated by those names.

I agree. There is no way it could be reliable for practical use.

[engl]

I think those who know what optical design their lens uses are also going to have a pretty fair idea of many degrees it covers. They'd also have a rough feeling for the amount of movements possible, which is as good as what a calculator using rough values would give.

That said, there are a lot of Plasmat design lenses that cover 70 degrees, Tessars that cover 55 degrees and Biogon-derivatives that cover 100 degrees :) Those being manufacturer specs for fairly recent general purpose lenses (not process) under 300mm, and of course, approximates.

[Jim Galli]

Sure. Petzval's 30° Cooke triplet, Heliar, Dialyt 50° Tessar 60° Plasmat 70° Dagor, Protar VII, G-Claron 80° Schneider Angulon 90° Super Angulon and Grandagon 105° Protar Series V 110°

Sure people here are gonna bust my chops all day long, but those are the numbers I've used fairly successfully. We're speaking in fairly broad generalities here. There are exceptions to every 'rule', but these should be useful. F'rinstance, some blowhard on Ebay bragging that his 210mm Heliar covers 8X10, I don't even have to ask.

Get yourself some graph paper and you can draw those angles out at different lengths and get decent enough image circle numbers. This is quick and dirty folks.

[Oren Grad]

Jim, as a seat-of-the-pants guide to make sure one doesn't get rooked by inflated claims about classic lenses on eBay, your list serves well.

But in a lens collection that's mostly modern and contains nothing really exotic, I've got plasmats that cover from 56 degrees (480 Sironar-N) to 80 degrees (Apo-Sironar-W), with lots of other coverage angles (64, 70, 72, 75) in between. And a tessar (450 Nikkor M) that behaves a lot like a G-Claron when you stop it way down. So if one is trying to find the right modern lens for a task, the generalization breaks down badly.

So it depends what the OP's purpose is in creating the calculator.

[Jim Galli]

Jim, as a seat-of-the-pants guide to make sure one doesn't get rooked by inflated claims about classic lenses on eBay, your list serves well.

But in a lens collection that's mostly modern and contains nothing really exotic, I've got plasmats that cover from 56 degrees (480 Sironar-N) to 80 degrees (Apo-Sironar-W), with lots of other coverage angles (64, 70, 72, 75) in between. And a tessar (450 Nikkor M) that behaves a lot like a G-Claron when you stop it way down. So if one is trying to find the right modern lens for a task, the generalization breaks down badly.

So it depends what the OP's purpose is in creating the calculator.

It is what it is. I think this is what the OP had in mind though.

[Mark Sawyer]

Part of the problem is that "coverage" varies by personal preference. Those who enlarge a 4x5 negative to 20x24 and want their image razor-sharp corner-to-corner will often find the acceptable circle of coverage fairly small. Those who contact print will find the circle considerably larger. And those optical perverts who thrive on swirls and soft corners in their portraits will go out of their way to find a lens with otherwise insufficient coverage that still illuminates and call it exquisite.

Jim's guidelines are a pretty good rule, but there really are quite a few exceptions. For a given focal length, I can usually get a pretty good sense of the illumination coverage by barrel proportions. But sharp coverage? You can get two 210mm f/6.8 Goerz Dagors separated by a few decades of manufacturing date, and one will cover an entire 8x10 sharply while the other has iffy sharpness at the corners of a 5x7...

Sorry if there was no useful information here, but that's how it is when things are a bit nebulous... :)

[Vaughn]

And RD Artars 46 degrees?

[domaz]

Thanks for the numbers Jim- my purpose with the calculator is in case I came upon a lens where I know the design I can look up the expected coverage. This is just for gross generalization, so I can quickly tell that "oh that Dagor probably won't cover 5x7 etc..".

If I really want to get crazy I could start making a database of lenses and coverage data from all the sources I can find but that is a big project to say the least.