Yet more confusion

[Resurrected]

So I bought my Nikon D5000 & then started reading all sorts of bumph. I thought I'd got my head around sensor size & the 1.5 multiplier to focal length.

But now I'm not so sure :shrug:.

I've just got the two kit lenses with the camera, an 18-55 & a 55-200. Both are DX. I had thought that the rule of thumb was that a DSLR that is not a full sized sensor has the 1.5 multiplier applied to the focal length you are using. However I've now read another article and think I have gotten this wrong.

Is it the case that if I use a DX lens on my camera that the focal length is exactly what it says on the tin but if I use a lens that is for a full size sensor then I apply the multiplier?

I confooooozed :bonk:

 

[TCR4x4]

The focal length is the focal length. An 18mm lens on a DX or FX body is still 18mm. The only difference is the DX camera only uses a small portion of the lens.

Imagine a big rectangular window with a view over a nice hill side. Now tape up the window so the rectangle is smaller.. Its the same view, you can just see less of it because some of it is covered up and your eyes percieve this as being zoomed in a bit.

A 50mm lens on DX is still 50mm, but because a portion is covered up so to speak it looks like the view you would get if you had rougly a 85mm lens on FX.

Basically, dont worry about it, it doesnt matter if you arent going to be upgrading to FX anytime soon.

 

[Resurrected]

Cheers Tom.

 

[MartynK]

As above. DX lenses are designated the same way as FX ones (50mm, 135mm etc), but the crop factor only applies on a crop (DX) body.

Confusion usually arises with the idea that the crop factor actually increases the focal length of the lens, so a 200mm lens becomes a 300mm lens on a DX body. It doesn't. As Tom explained, the focal length remains the same so the subject is reproduced at the same size, but it appears to be larger in the frame/image because the field of view is smaller. The rest of the frame has been "cropped" out, as if you had cropped the image in post processing, but without losing the pixels.

Some people buy FX lenses to use on their crop body, because a particular lens, or the one they want, is only available in this format; which is the case with all of Canon's L series lenses. That's fine, but they're more expensive and I wouldn't worry about it unless you want to future proof your glass because you're planning to move to full frame.