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05-05-2011, 08:53 PM   #1
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Looking For Diagonal FOVs...

Hi, after many researches I still can't find the following FF lenses respective Angle of View into a ASPC body:

Tokina 20-35mm AT-X Pro F2.8

FF FOV: 93.38 - 63.13

Tamron SP AF 17-35mm F/2.8-4 Di LD Aspherical [IF]

FF FOV: 104 - 63

Tokina AT-X Pro 28-70mm f2.6-2.8

FF FOV: 75.3 - 34.3

Tokina AT-X 280 AF PRO 28-80mm f/2.8

FF FOV: 74.20 - 35.20

Sigma 120-400mm f/4.5-5.6 DG APO OS HSM

FF FOV: 20.4 - 6.2

Tamron 70-200mm F2.8 Di LD Macro

FF FOV: 34 - 12

Tokina AT-X 840 AF II 80-400mm F/4.5-5.6

FF FOV: 29.50 - 6.13

Tokina AT-X 828AF PRO 80-200mm F2.8

FF FOV: 30.20 - 12.20

Sigma 150-500mm f/5-6.3 DG HSM APO

FF FOV: 16.4 - 5


I've tried converting the lenghts by dividing them by 1.5 and look for their respective ASPC angle values but that didnt seem to be accurated :x

Is there a simple way of finding that out? am I doing the wrong maths?

Give me an example please

Thanks in advance!


Last edited by Thales454; 05-05-2011 at 11:00 PM.
05-06-2011, 02:22 AM   #2
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This chart has the answers: https://www.pentaxforums.com/forums/pentax-lens-articles/93714-field-view-tab...d-645-6x7.html

Keep in mind that manufacturers generally report diagonal fov, as the number is bigger!
05-06-2011, 11:01 AM   #3
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W00T! Thank you very much Adam =DD
05-06-2011, 11:17 AM   #4
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As Adam notes, that chart is the horizontal field of view, so if you want diagonal, it won't really help.

Rather than using a table, if you have a scientific calculator handy, then the math is pretty simple.

The APS-C sensor used in Pentax bodies has dimensions of approximately 23.7x15.7 mm, with a diagonal of approximately 28.4 mm. This is for the K-5; sensors in the other cameras might be very slightly different (probably within 0.1 mm).

The formula for calculating APS-C diagonal field of view (DFOV) on a rectilinear lens is simply:

DFOV = 2 * arctan (14.2 / f)

Where "f" is the actual focal length of the lens, in mm, not adjusted for any crop factor. The "14.2" represents half of the diagonal dimension of the sensor, so if you want (for example) a horizontal field of view, use half the horizontal dimension in its place. You can substitute dimensions taken from full-frame, 4/3, or whatever you like, as long as you can figure out what the true dimensions are. And if you have your calculator's angle measurement set to degrees, your DFOV output will also be in degrees.

(On a calculator, the "arctan" function is usually marked "Tan-1" with the "-1" superscript, but I can't figure out how to show that superscript in this text!)

So for a 70mm focal length, I'd do this (reading from left to right):

DFOV = 2 * arctan (14.2/70) = 2 * arctan (0.203) = 2 * 11.5 = 23.0 degrees

And so on!

This will give you a good idea of what a lens's field of view will be. But it won't necessarily be 100% accurate -- manufacturers don't exactly quote precise focal length numbers (e.g., a "20mm" lens might actually be 1-2 mm off from that), and focal length might vary as you focus from near to far, sometimes by quite a lot, depending on the lens.


Last edited by Quicksand; 05-06-2011 at 11:23 AM.
05-06-2011, 02:47 PM   #5
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QuoteOriginally posted by Quicksand Quote
This will give you a good idea of what a lens's field of view will be. But it won't necessarily be 100% accurate -- manufacturers don't exactly quote precise focal length numbers (e.g., a "20mm" lens might actually be 1-2 mm off from that), and focal length might vary as you focus from near to far, sometimes by quite a lot, depending on the lens.
Well, I actually used that chart to make sure the maths I did using the following online calculator was correct and they all seemed to be pretty accurated and matched precisely.

http://www.tawbaware.com/maxlyons/calc.htm

All answers I got ranged from 1 to 2 degrees according to the manufacturer's FoV, so I'm quite happy with it =D

But thanks for your insight, that might be useful as well in case I find myself away from the computer.
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