focal length question

G

grahamdunn

Active member
Hi there,
I've been learning about still lenses a bit recently but still have a point of confusion hopefully someone can explain.

On still SLR lenses, a Nikon 16mm, for example, looks "wide" on film because of the information the film can actually hold, whereas on a digital still camera, it will look less wide, perhaps more like a traditional 28mm might look (because the CCDs can't take in as much info I believe). So...the question is, how does focal length work for an adaptor? Since the camera "sees" the ground glass and the SLR lens' back focus is set to hit the ground glass, it seems that maybe the focal length of a 16mm lens would be truer to a traditional wide lens, and would not actually be closer to a 28mm width. Is this correct, or if not, is there a way to figure out the focal length conversion? Thank you, hope this makes some sense...
—Graham
 
I think i know what youre saying....


Yes. the field of view on a video camera with a 35 adapter is almost identical to that of the "film" equivalent.
 
The focal lenght of a lens means NOTHING if you don't relate it to the sensor size:

An 80mm lens IS "normal" for a medium format camera (60X60mm ) film or digital.
The same focal 80 (or most common 85) is a "medium telephoto" on a 35mm film camera and...
The same 80 mm focal means a telephoto lens on a digital camera. (giving you the loks of an 135mm lens on a film camera) because of the cropp factor of 1.7.

In short the lens coverage (of the imging size) and the field of view dictate the "looks" of a lens.

A 35mm lens is a WIDE angle on a Nikon/Canon still film camera (24/36mm)
"normal" in motion picture (18/24 )
and also "normal" in a digital camera (factor the sensor 1.6 or 1.7 magnification)

I guess someone skilled should dig up some related diagrams and post the links.
I remember finding them on the net (or check the tutorials in this section)
Hope this helps.
Best,
Dan
 
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