Proper way to figure AoV/FoV

[Shootist]

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What formula is used to figure the AOV/FOV of different lenses for the 1.33 crop of the M8.

I have been using "Stock AOV/FOV "/" 1.33 = AOV/FOV for M8.

But this doesn't seem right when comparing it to the calculated focal length.

A 24mm has a AOV/FOV of 84d on 35mm film. If you take the 24mm and "Times" it by the crop 1.33 you come up with 32mm when used with a M8. BUT if you take the listed AOV/FOV of 84d and "/" by 1.33 you come up with 63.xxxxd. Now a stock 35mm has a listed AOV/FOV of 64d.Which is greater then the 24mm, on a M8, AOV/FOV of 63.xxxxd, dividing by the crop factor of 1.33, and yet it is a 32mm lens on the M8.

What should I be dividing by.

[DennisAllshouse]

The angle is not a linear function like focal length. There is a tangent function involved. I haven't work out the formula. I've been meaning to but it's late here(east coast usa). Seriously you have to look at the geometry of focal length and angle of view to get the relationship.

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[DennisAllshouse]

I couldn't go to bed without figuring this out:

 

AOV = 2*arctangent((1/2*sensor diagonal)/focal length)

 

I'm using the asterisk for multiplication, slash for division, arctangent is the inverse tangent. It's hard to spell without superscript.

 

In the above formula, use 43.26666 for diagonal and 50 for focal length gives 46 degrees for 35mm.

 

For APS-C sensors, diagonal is 28.84444mm, 50mm focal length gives 32 degrees.

 

I don't have M8 dimensions handy.

 

I hope this helps.

 

Dennis

[masjah]

Use 32.45 for the M8 diagonal (that DOES scale linearly with the "crop factor").