View Full Version : Zoom mm ratings - film equilavent . .?

06-11-2005, 01:05 PM
Lately I have been a little confused with the mm length of zoom lenses. In the EXIF data of a fully zoomed S2 shot it would say 72mm yet whenever I read about the zoom, it says something like 38mm to 400mm.
I have a feeling the answer is something like film equilavent, but never going near touching a film camera I know nothing about them so do not really understand the film equilavent meaning.
Could anyone explain to me what these mm lengths actually mean and what I should look out for and understand about them.
I presume the lower the number the more zoomed out the full wide angle is?

Thanks for any help regarding this subject :)

06-11-2005, 01:53 PM
It has to do with the sensor size vs the glass size. The "phsyical" zoom length was 72 mm at max telephoto which on that sensor equates to a "35mm equvilant" of 432mm. Just multiply by 6 for your "35 mm focal lengeth" on your S2.


06-12-2005, 08:48 PM
Nearly all digital cameras have sensors which are smaller than regular film ... because of this, to get the same field of view as, say, a 50mm focal length lens would show on film, a digital camera would need a shorter focal length. For example, on a Panasonic FZ20 the same view would be achieved by about an 8mm lens .. on a Canon Digital Rebel SLR the required focal length would be about 32mm.
Because of the many different sizes of sensors used in digital cameras, it's become common practice to list the "film-equivalent" mm rating of a lens, so that we have a standard measure of the FOV of any given camera.
You're correct about the smaller numbers being wider angles. However, becase of what was stated above, note that a 6mm wide angle on a superzoom camera would actually be *less* wide than a 28mm wide angle on a film camera, for example. (The 6mm has a 36mm FOV in film-terms)
In "film-equivalent" mm, a 50mm lens is about 'life-size', while 35mm is a standard wide-angle.