A question about lenses and lens factor

[jands0607]

Do focal lengths change based on lens AND sensor size, or just sensor size? For example, I have a D90 and the 18-105mm kit lens. If I understand correctly, this lens was "made" for a crop body like mine. But what if I buy a lens that is made for a full body? Such as the Sigma Wide Angle 28mm f/1.8 EX Would 28mm on the Sigma be the same as 28mm on my Nikkor? Or would it be subject to the 1.52 lens factor, making it seem 42mm? Is my Nikkor getting magnified at 1.52 also?

Hope that makes sense. Thanks for the help.

[jdepould]

Lenses are all labelled using the same standards, regardless of the image circle size (that's where crop factor comes in).

You would use the 1.5 crop multiplier regardless of the lens.

Having said that, it doesn't magnify in the sense that a teleconverter magnifies. You're simply pulling the middle of the image out. The field of view changes, but the apparent magnification does not.

[jands0607]

That clears things up... thanks for help!

[Almond.Butterscotch]

a 50mm lens is a 50mm lens is a 50mm lens- the image coming through the glass is focussed on the same plane (where the sensor/film would be). As jdepould said, the multiplier just shows you how much you need to multiply the focal length by to see what you'd see on a 35mm/FX camera.

So if you have a 28mm lens, then you'd see through your D90 what someone with a D700 with a 42mm lens would see.

[zetson]

Originally Posted by Almond.Butterscotch

a 50mm lens is a 50mm lens is a 50mm lens- the image coming through the glass is focussed on the same plane (where the sensor/film would be). As jdepould said, the multiplier just shows you how much you need to multiply the focal length by to see what you'd see on a 35mm/FX camera.

So if you have a 28mm lens, then you'd see through your D90 what someone with a D700 with a 42mm lens would see.

Correct, if you don't take the perspective into account.