#### grebeman

##### Mu-43 All-Pro

- Joined
- Mar 13, 2010

- Messages
- 1,203

- Real Name
- Barrie

So a m4/3 sensor has a diagonal of just under 22mm, a 35mm negative has a diagonal of 43mm, a 21/4" square negative has a diagonal of 79mm, a 6x9 negative has a diagonal of 105mm, a 4x5" negative has a diagonal of 155mm. The standard lenses for these formats were always regarded as 50mm for 35mm, 80mm for 21/4" square, 105mm for 6x9 and 150mm for 4x5".

When you divide the diagonal of the negative by the standard focal length for each format the result is approximately 1 for each of these. If you use a lens of shorter focal length the number obtained is greater than 1, if a longer focal length lens is used, the number is less than 1.

Therefore on m4/3 the standard lens should be about 22mm focal length, lets call it 20mm and for simplicity and easy calculation lets call the sensor diagonal 20mm

Fit a 50mm focal length lens and do the simple mathmatics and the result is 20/50 = 0.4, therefore on m4/3 a 50mm lens is a long focal length lens, on 35mm the result is 43/50 = 0.86, on 21/4" the result is 79/50 = 1.58. Exactly the same focal length lens, different results on each format, different perspective obtained.

diagonal/focal length vs angle of view

0.35 = 20 deg

0.54 = 30 deg

0.73 = 40 deg

0.93 = 50 deg

1.15 = 60deg

1.40 = 70 deg

1.68 = 80 deg

2.00 = 90 deg

2.38 = 100 deg

2.86 = 110 deg

Barrie