Most people are aware changing the format; eg MicroFourThirds, 35mm full frame, 5 x 4 large format etc, changes the field of view. So a 25mm lens on a MicroFourThirds camera has the same field as a 50mm on 35mm and approximately 150mm on 5 x 4.
What fewer people realise is the impact on aperture and ISO.
Recently Chris posted a video that covered this area quite well.
One thing I never see mentioned is the impact on perspective.
So does the rule about field of view also apply to perspective?
People are advised when shooting a head and shoulders portrait to use a focal length of 85mm (35mm full frame), as this gives a pleasing perspective. It flattens perspective giving a more pleasing look to the face.
But what if you are a MicroFourThirds user. Does a 40mm lens give a similar perspective affect as that of a 85mm on full frame?
Well, we know the field of view is close to the same so let’s try a thought experiment.
Stand about 10 metres from someone and stare at their face; now do the same at 1 metre and finally 0.1 metre. The closer you get the more the perspective changes and their nose gets bigger and bigger, its the same as if you use a wide angle lens and shoot them from a distance with a very high resolution camera, zoom right in and the perspective is quite flattened. Walk close and take the same picture and the features become more pronounced.
They say the 85mm lens makes the nicest portraits on 35mm and that is because it forces you to stand far enough away to make the perspective pleasing.
The perspective is a result of the camera to subject distance and not the lens.