Lens on a crop lens camera?
If I put a 50 mm 1.8 lens on a Canon D7 or a Nikon D7000, is it still 50mm? Even if the lens is a DX Lens for Nikon? I'm confused.
Yes it is still 50mm but it will give you the field of view of a 75-80mm lens on a full frame or film camera. The smaller sensor on the APS-C cameras gives you the crop factor but the lens is still the same size.
On a DSLR… Forget all about the "crop factor", it doesn't mean anything. The only thing that matters is how the lens frames the shot you want.
If a camera has a 1.3x "crop factor" with the 50mm, it will frame like a 65mm lens would on a full frame camera. If the camera has a 1.6x factor, then the lens behaves like an 80mm… BUT the lens is still a 50mm. It is just a matter of using what gives you what you want.
For example, when I shoot I don't say "Well, I need the framing view of a 150mm lens on a full frame camera, so 150/1.3 is 115.384615mm". Instead, I just grab the lens that I know will give me the framing I want… Or at least close to it. I MIGHT grab a 100mm (which would be a 130mm equivalent and take a step or two forward) OR grab my 70-200 and zoom until it frames how I want, but I don't bother looking at the lens guide to see what it shows… I look through the viewfinder and say "that's the shot I want.
This site may help unconfuse you.
First, it isn't "crop lens" its "cropped sensor".
This explains the concept of the "cropped sensor":
http://www.photographymad.com/pages/view/crop-factor-explained
The actual focal length of a lens remains the same whether its on a "cropped sensor" or full-frame DSLR. What changes on a "cropped sensor" DSLR is the equivalent angle of view of the lens. A 50mm lens on a Sony or Pentax or Nikon DSLR - all of which have a 1.5x "crop factor" - will have the equivalent angle of view of a 75mm lens on a 35mm film camera or full-frame DSLR. A 50mm lens on a Canon DSLR - which has a 1.6x "crop factor" - will have the equivalent angle of view of an 80mm lens on a 35mm film camera or full-frame DSLR.
This site shows the equivalent angle of view of lenses on a Canon "cropped sensor" DSLR:
http://www.sweeting.org/mark/lenses/canon.php
This site shows the equivalent angle of view of lenses on a Sony, Pentax or Nikon "cropped sensor" DSLR:
http://www.sweeting.org/mark/lenses/nikon.php
On a Sony or Nikon or Canon full-frame DSLR a 50mm lens will have an angle of view of 39"5'.
On a Sony or Pentax or Nikon "cropped sensor" DSLR that same 50mm lens will have an angle of view of 26"39' while on a Canon "cropped sensor" DSLR its angle of view will be 25"34'.
The lens doesn't change - it's still a 50mm - the lens isn't "cropped" - the sensor is "cropped".
All you need to know is that on camera with a cropped sensor, with a 1.6x crop factor for example, a 50mm will be equivalent to an 80mm on a full frame camera.
1.6 x 50 = 80