Focal Length Equivalency Table

I’ve decided to write a page outlining some common focal lengths for different formats and their equivalency in other formats, it’s something that I never bother to calculate myself but often find that I’ll do a google to get the information, I’ve seen several tables online but wanted to create a page to keep all the information that I need in one place thats easy to get to.

Hopefully this information can help you too.

Since most people have started with or use 35mm or Full Frame I’ll use this as a basis for comparison, most of the world does the same so I’m not going to change anything. In the table below you’ll see common focal lengths on multiple formats with the equivalent focal length and angle of view listed.

Caveat lector: These are not exact angles of view, i’ve had to average them to get the equivalents right and not all manufacturers release lenses in the below focal lengths, the below figures will get you in the ballpark only, for precise results please do your own calculations

 

Angle of View (average) 35mm (full frame) Medium Format 6×4.5 Medium Format 6×6 Medium Format 6×7 4×5 Sheet Film 8×10 Sheet Film
73deg 24mm  43mm  35mm  55mm  85mm  200mm
54deg 35mm  50mm  60mm  70mm  120mm  250mm
39.5deg 50mm  75mm  80mm  90mm  150mm  350mm
24deg 85mm  120mm  135mm  160mm  300mm  600mm
15deg 135mm  200mm  210mm  250mm  480mm  980mm

My above number are calculated for horizontal angle of view, if you would like to do your own calculations then read below for the formula.

For a lens projecting a rectilinear image, the angle of view (α) can be calculated from the chosen dimension (d), and effective focal length (f) as follows:[3]

\alpha = 2 \arctan \frac {d} {2 f}

Example

Consider a 35 mm camera with a lens having a focal length of F = 50 mm. The dimensions of the 35 mm image format are 24 mm (vertically) × 36 mm (horizontal), giving a diagonal of about 43.3 mm.

At infinity focus, f = F, and the angles of view are:

  • horizontally, \alpha_h = 2\arctan\frac{h}{2f} = 2\arctan\frac{36}{2 \times 50}\approx 39.6^\circ
  • vertically, \alpha_v = 2\arctan\frac{v}{2f} = 2\arctan\frac{24}{2 \times 50}\approx 27.0^\circ
  • diagonally, \alpha_d = 2\arctan\frac{d}{2f} = 2\arctan\frac{43.3}{2 \times 50}\approx 46.8^\circ

note: The above formula have been sourced from the Wikipedia page on Angle of View, consult there for further information.

 

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