# Setting up the right camera lens length

Hi,

I’ve inserted a photo as wallpaper (1620 x 1080, taken with 21 mm lens) and i’ve made my viewport with the same aspect ratio as the photo (1.5:1). But if i change the lens length to 21 mm in Rhino, the geometry i’ve created does not match at all with the photo wallpaper. How can I calculate the right lens length so that it matches the photo?

Kind regards,

Rutger

PerspectiveMatch should help.

What size sensor/negative was used when taking the imported photo? Was the lens focal length actually 21mm or was it 21mm “equivalent”? Focal lengths in Rhino are specified as equivalent for a 35mm camera (24mm x 36mm sensor/negative). So if the photo was taken with a camera with a smaller sensor/negative then the equivalent focal length would be needed, not the actual focal length.

Thanks for your reply. The photo is taken with a Canon EOS 550D… the size of the sensor is 22,3 mm x 14,9 mm… which means that the aspect ratio is the same as the 24 x 36 mm (1:1.5) So how can i calculate the equivalent focal length? I’ve noticed that the right focal length in rhino should be between 35 and 40 mm but I would like to now it precisely…

I have tried PerspecpectiveMatch but somehow it isn’t as precise as I hoped it would be… Thanks for your reply though

Equivalent focal length = Actual focal length x 36 mm / Sensor width (assuming 3:2 sensor proportions)

So for a 550D with a 21 mm actual focal length lens

Equivalent focal length = 21 mm * 36 / 22.3 = 33.9 mm