I have a Nikon D80 DSLR camera which is not full format (FX) but rather DX, and I'm using the 18-135 mm DX kit lens. I also own a Nikon 50mm f/1.8D lens, which is supposed to be 50mm for FX cameras, as it is not specifically for DX cameras (there is a separate DX lens of the same variety).
The lens I own is exactly this one: amazon.com/Nikon-50mm-Nikkor-…
The reviews also say that this lens effectively is 75mm for use in DX cameras. I had always assumed that my lens was effectively 75mm while taking pictures. however yesterday I decided to compare my two lenses: I shot the same scene with both 50 and 75mm focal lengths with my kit lens, then shot with my 50mm prime lens. To my surprise, the picture from the 50mm lens was exactly the same with the 50mm on my kit lens, not the 75mm.
So I'm completely dumbfounded, why is this so?
Your 75mm lens is actually about 112.5 mm on a DX body.
It's not compared to another lens on your camera, it's compared to using the lens on a full frame camera.
Full frame cameras are the true mm. Crop sensors are roughly 1.5x to 1.6x the mm listed on the lens.
EVERY lens at 50mm will be roughly 75mm. every lens set at 75mm will be roughly 112.5mm on your camera.
It's not the lens that is different, it's your camera's sensor that is a different size from a FX camera sensor.
50 mm is still a 50 mm on yours, DX, or a FX camera.
Think of it this way. You're inside a room, and looking out a window. a FX is wide open window. a DX view is 2/3 open window.
