Focal Length Multiplier

[Mike McCarty]

In the olden days of 35mm film it was correct to accept that an 85mm (+-) focal length was the optimum for portraiture. For most digital SLR's that we discuss here (with the exception of a precious few costing many thousands of dollars) this benchmark 85mm focal length has been dropped to 57mm (85 / 1.5 = 57). This 1.5 FLM would be applied to my digital Nikon SLR, others, such as the Canon, would have a slightly different multiplier.

It is the size of the sensors (which vary slightly between manufactures), as they relate to the size of 35mm film, that brings about the need for this calculation.

The 85mm benchmark is now a relic of the days of film. All the optical attributes of the 85mm focal length have been transported to the new number: 57mm (+-). This is true whether you are using the new digital lenses or the lenses you used on your old 35mm film camera.

For a more in depth discussion of this subject you can refer to the following link:

http://www.dpreview.com/learn/?/key=...gth+multiplier

[Julie Deane]

Thank you, Mike, for making this clear. It will really help for the day when I can afford a digital SLR.

I had been thinking that the standard kit lens was too short (55 - 70 mm). Now it appears that it is actually the approximate equivalent of a 85 -105 (film) lens. As someone used to the old style lenses, this conversion info helps immeasurably.

[Mike McCarty]

It's an unfortunate complication, but one that could not be avoided I suppose. Most people who use these cameras won't ever consider this obscure detail, but it's something for us to take note of. I think if I have to remember one more thing I'm going to pop.

As technology marches predictably forward, and the fact that a couple of the very high end cameras of today have a 1:1 conversion, the Focal Length Multiplier may also become a relic of the early days of digital. As Chief Dan George once said to the outlaw Jose Wales: "We must endeavor to persevere."