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Jack Flesher
29-Apr-2007, 11:04
I am sure this has been done many times before, and I thought I saw it somewhere online some time ago, but I could not find one so I built one.

If anybody wants to build their own, here is the formula for Excel. Given both the lens focal length in mm (or inches) and angle of coverage in degrees, it will calculate the lens' total available Image Circle in mm (or inches).

Formula for the Image Circle cell is: =2*(TAN((ENTRY CELL LOCATION FOR INPUT OF LENS' ANGLE OF COVERAGE/2)*PI()/180))*ENTRY CELL LOCATION FOR INPUT OF LENS' FOCAL LENGTH.

Example. In my spreadsheet, cell D7 is where I input the lens angle of coverage and B7 is where I input the lens focal length, and the formula is this: =2*(TAN((D7/2)*PI()/180))*B7

Mods: If this is redundant or old news, please feel free to delete it.

Cheers,

Ash
29-Apr-2007, 11:09
Brilliant, thanks!

I was thinking the other day whether I could nab the calculation and sort all my lenses into a spreadsheet :D

Oops, then I re-read and wonder, how do I find out angle of coverage?? *embarassed expression* !

Gordon Moat
29-Apr-2007, 11:41
Would that only work for one aperture? The reason I ask is that in Schneider lens specification (probably in other companies too), the coverage is different for wide open, and (for example) f22.0. That implies that the coverage angle changes with aperture.

Ciao!

Gordon Moat
A G Studio (http://www.allgstudio.com)

Jack Flesher
29-Apr-2007, 12:58
Hi Gordon:

Absolutely, a lens' angle of coverage changes with aperture. Most manufacturers will spec the angle of coverage with a specific aperture, usually f22 and sometimes f16 or f32 for large format lenses, and some manufacturers will also include the spec for wide open.

The spreadsheet requires you to input angle of coverage, so depending on what value you enter, you will get different output values. In this fashion, assuming you had the AoC spec for each aperture of a given lens, you could conceivably generate a table of IC's for each aperture using the formula.

Cheers,

Jack Flesher
29-Apr-2007, 13:00
Oops, then I re-read and wonder, how do I find out angle of coverage?? *embarassed expression* !

It's often spec'd by the manufacturer for a given family of lenses...

Ash
29-Apr-2007, 13:23
Ah, no joy for me then; I wanted to work it out for my two Goerz lenses (Dagor, Dogmar) a Ross Xpres, an un-named brass barrel lens, Cooke Process and Aviar lenses, and a few other pieces like the Hanimex 300mm slr front cell.

Jason Greenberg Motamedi
29-Apr-2007, 15:11
There is a nice web based calculator at Chad Jarvis's site:

Ash
29-Apr-2007, 15:21
Thanks Jason!

Jack Flesher
29-Apr-2007, 16:23
There is a nice web based calculator at Chad Jarvis's site:

That's the one I was looking for :)

Jason Greenberg Motamedi
29-Apr-2007, 18:07
Thanks Jason!

Ah, don't thank me, thank Chad. He used to hang about here, does he still?

jason

Ernest Purdum
29-Apr-2007, 20:30
Being rather anti- math, I prefer to draw and measure. Draw a horizontal line near the bottom of a piece of paper. This is the center line of your lens. Near the left side, use a protractor and start another line at half of the angle of view. Measure along the horizontal line to your focal length. Connect the two lines with a vertical line starting at the focal length mark. The length of the vertical line between the two other lines is one half of your image circle.

If you know the image circle, but not the angle of view, you can do it backwards to find the angle.

Doremus Scudder
1-May-2007, 01:18
I know that many lens designs have angles of coverage associated with them. For example, plasmats are all about the same AoC, Gauss designs another, etc.

Does anyone know off the top of their head which AoC goes with which designs? The info would be approximate of course, but helpful for the above calculator.

Jack, thanks for the great tool.

Best,

Doremus Scudder

AuditorOne
23-Jul-2016, 21:47
I know that this was posted a very long time ago but it is a very easy method to use. Thank you very much.

Pfsor
24-Jul-2016, 04:29
I am sure this has been done many times before, and I thought I saw it somewhere online some time ago, but I could not find one so I built one.

If anybody wants to build their own, here is the formula for Excel. Given both the lens focal length in mm (or inches) and angle of coverage in degrees, it will calculate the lens' total available Image Circle in mm (or inches).

Formula for the Image Circle cell is: =2*(TAN((ENTRY CELL LOCATION FOR INPUT OF LENS' ANGLE OF COVERAGE/2)*PI()/180))*ENTRY CELL LOCATION FOR INPUT OF LENS' FOCAL LENGTH.

Example. In my spreadsheet, cell D7 is where I input the lens angle of coverage and B7 is where I input the lens focal length, and the formula is this: =2*(TAN((D7/2)*PI()/180))*B7

Mods: If this is redundant or old news, please feel free to delete it.

Cheers,

What complete nonsense this thread is! First of all its title is nonsense - as you can read the OP doesn't want to calculate an angle of coverage but the image circle size. (Given both the lens focal length in mm (or inches) and angle of coverage in degrees, it will calculate the lens' total available Image Circle in mm (or inches) says the OP.

Secondly, as the OP says elsewhere (post. n.4) - "Most manufacturers will spec the angle of coverage with a specific aperture" - it is also true that most manufactures spec both the angle of coverage of a lens and its image circle size.

Gosh, I will give you a calculator that calculates something you need to know as input first and then it will calculate what I did not say in its name. Heck, thank you for that!