View Full Version : A Question About Prime Lenses

Chance White
10-09-2008, 08:05 PM
Okay so as I understand it, for example, the 50mm prime is actually equivalent to a 75mm telephoto mounted to the D90... this is true for all prime lenses? Does it also work like this with 35mm adapters?

Always a 1.5x multiplier?

Is this also true for zoom lenses?


Steve Castle
10-09-2008, 08:35 PM
Not just prime lenses, all lenses mounted to a cropped sensor relative to a full-frame 35mm. Its all relative. For instance for a 6x7 medium-format camera a 50mm lens is equivalent to a 25mm in a 35mm.

Here's a resource:

Chance White
10-09-2008, 09:02 PM
Excellent! Thank you.

10-10-2008, 12:24 PM
This is true, but also remember that a 50mm on a D90 is about the same as a 50mm in Super35. The crop factor is relative to field of view offered by the lens on a 35mm still camera.

Also, for a given field of view, aperture, subjects and focus you have roughly 1 stop deeper DOF with a D90 compared to a 35mm still camera. So, roughly speaking, a 35mm at f2 on a D90 is like a 50mm at f2.8 on a full frame camera.

Chance White
10-10-2008, 01:23 PM
Thanks Thebes...

Man, this is getting a little confusing! So, basically, should I just not worry about the fluctuations and just get the right lenses I need... I was concerned because for example if I need a wide lens, I'd want a 28 or 24mm aesthetically but does that mean I need to buy an 18mm to achieve the 28mm look? Or can I just get a 28mm? It sounds like from your response I can just do the latter... is this correct?

Also, how does this work with 35mm adapters? If I'm shooting on an HVX200 + adapter + 28mm 2.4 prime plus a D90 with the SAME lens, is it going to be the same, focal view and DOF wise? Do the 35mm adapters have the 1.5x crop factor as well?

Or, since S35 also has the crop factor, should we just not even worry about it?


Michael Carter
10-10-2008, 07:12 PM
All-of-the-above only applies to "film" lenses - Nikon's DX ("digital") lenses are sized for the smaller sensor; you can mount them on a film body, but you'll get some serious vignetting.

10-11-2008, 03:24 AM
And to confuse you even more, Nikon does indeed have a 1.5x crop factor, whilst Canon uses a 1.6 on their consumer and prosumer cameras and 1.3x on their 1D (not to be confused with high megapixel fullframe 1Ds) professional cameras.