Calculating reach for wildlife photography

Bird and wildlife photographers are concerned with the reach of a camera and lens setup. Let’s define reach as the number of pixels per degree. If you’re a bird photographer, more is generally better. Here’s how to calculate reach given the focallength of the lens and the pixel pitch of the sensor.

Let:

• p = pixel pitch (in mm per pixel)

• f = focal length (in mm)

• Reach = pixels per degree (horizontal)

Then:

Or numerically simplified using the small-angle approximation (since tan(0.5°) ≈ 0.0087265):

If:

• p = 0.0046 mm (i.e., 4.6 µm pixel pitch)

• f = 500 mm (lens focal length)

Then: