Maybe this will help clear up some of the confusion about field-of-view and "35mm equivalent" when comparing full-frame cameras and those with crop-sensors.
Regardless of the 'comparison', a 50mm lens is a 50mm lens, no matter which sensor you're using. What changes is the
apparent field of view between the two. So if you were to take a full-frame and a crop-sensor camera, set them up side-by-side with, say, 50mm lenses on both, and looked through the viewfinders of them, this is what you would see:
Neither camera-lens combination 'enlarges' or 'reduces' the apparent size of the subject. The bridge and the flowers are
the exact same size in both VFs. What is different is the
size of the focus screens, which is in direct proportion to the
size of the respective sensors. This, in turn, changes the field of view (measured in degrees).
The comparison shown is
both lenses being the same focal length. They're not meant to show the differences in detail, sharpness, resolution, contrast, etc.. or the differences between the abilities of the two sensors. Besides, they're reduced so much from their original full-size dimensions you can't use them to compare those parameters anyway.
Notice the difference is the
size of the images. That is because the
sensors are not the same physical size. This is reflected in the size of the images. If you were to set a FF and crop sensor side-by-side the viewfinder in the FF camera will be larger.... because it must reflect the larger sensor.
Everything is the same size in both images because the
sensor is smaller. The lens
projects a subject the same size.... it doesn't know which sensor is sitting behind it.
To show this, here's my D600 ("Full Frame/FX") and my D7000 ("Crop Sensor/DX"), side-by-side, with both in
Mirror Up for Cleaning mode.
The blue-green rectangles are the actual sensors. Notice how the FX sensor on the left is larger (Nikon specs are 24m x 35.9mm) than the DX sensor on the right (Nikon: 23.6mm x 15.6mm)
I put a 50mm
FX lens on the D600, it sees this:
When I put a 50mm
DX on the D600, it sees this:
This is
exactly what you would see in the viewfinder as well. These images are merely reduced in scale for posting here. No other editing was done. Notice how everything in the scene is rendered the same size?
The only difference between the two is the DX lens is not designed to cover the entire FX sensor.... it only needs to cover the smaller DX sensor. That's why the DX lens shows the black areas... both in the VF and on the sensor.
If I put either the FX
OR the DX lens on the D7000 (crop sensor) , or on the D600 and shoot in DX mode, they will both record this:
When I enlarge the DX image to
match the same dimension of the FX image, it appears I'm using a longer lens. I'm not. They're both 50mm. What changes is the
field of view caused by the 'crop factor' of the smaller sensor.
An analogy would be like putting a film negative into an enlarger and running it up to make an 11x14. Then replace the 11x14 with a sheet of 8x10......
without changing anything else. The subjects in the 8x10 will measure the same as they are in the 11x14. There would also be no more detail in one compared to the other. Or, you could take the 11x14 and cut it down with scissors to an 8x10.... there would be no more detail when you're done doing that.