Crop camera lens questions

[Clinton1]

Hey all,

I have some questions relating to my D80 and lenses.

I understand that the D80 is a crop camera, and the ratio of the sensor size to 35mm format is a 1.6 ratio.

This means that I need to multiply the focal length of a lens that is for 35mm by 1.6 to find out what the focal length on my camera would be.

For example, the 18 - 55 mm lens (35mm format) that came with my camera is really a 28 - 88mm lens on the D80. ???

I think I am correct... please correct me if I am wrong.

I believe that the picture angle of the lens changes as well on the crop format camera's.

Is there a way to work out the picture angle change (other than looking up the Nikon site)?

For example:
I'm looking at getting an 'effective' 50mm lens for the camera... that means that I am looking at a lens with a focal length of 35mm.

The specs say that the lens is a 62 degree in 35mm format, and 44 degree in my D80's DX format.

Finally, does this also affect the "closest focusing distance"?

Other than 'general interest' the reason I am asking is that I am looking at getting one or two primes for the camera, and will be straying outside of the DX lens range.

Any and all advice will be greatly appreciated.

[Mike]

It's easiest to look through the camera, on a DSLR Its WYSIWYG (your'e right about the 1.6 aspect ratio)

[macropod]

Hi Clinton1,

The D80's sensor measures 23.6*15.8mm, compared to 36*24mm for 35mm film. Therefore the crop factor is 1.53. Most users just round this off to 1.5.

The crop factor has no effect at all on the focal length. Rather, it is the field of view that is cropped. For example, suppose you're after a 15*10cm print. If you take the picture with the D80 using a 50mm lens, the effect is essentially the same as you'd get using a 35mm camera with the same 50mm lens, enlarging the print to 23*15.33cm then cropping the print down to 15*10cm.

When people talk about the crop factor being a focal length multiplier, what they're really talking about is the fact that the cropped field of view is the same as what you'd get if you used a 35mm camera with a lens whose focal length was increased by the crop factor. In the case of the D80 with a 50mm lens, the field of view is the same as a 35mm camera with a 50*1.53 = 76.5mm lens.

What is often overlooked in the equation, though, is that, other things being equal, the cropped image will have more depth of field than the uncropped one.

As for your other questions:
1. For a spreadsheet to calculate DoF, angles & fields of view, plus a lot of other useful stuff, see my posts at: http://photography-on-the.net/forum/showthread.php?t=408465
2. Close focussing distance is unchanged

Cheers

[Clinton1]

Hmmm... Going to have to think about that.
Great info in the link, Macropod. Thanks.