Nikon DX Lens / crop sensor question

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chris330

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Not sure if this will make sense or not, so here goes! :lol:

I've got a D90 with the DX 18-105mm kit lens. Now I know that if you use that lens on a full frame camera you'll end up with a cropped view. Also if you use a full frame lens like the 50mm 1.8 prime on the D90, you have to taken into account the crop sensor so it ends up more like a 75mm equivalent on a full frame camera. Likewise the 35mm prime ends up like a 50mm equivalent etc.

So my question is, does the DX lens on the DX format camera represent what an FX lens on an FX camera is? ie will you get the same field of view with a D90 with the DX 18-105mm set at 50mm as a D700 with an FX 50mm, or is it like a D700 at 85mm?

I'm thinking about getting either the 35mm prime or the 50mm 1.8 prime, so what I'm trying to figure out is will the 50mm prime give the same field of view as my 18-105 at 50mm or 75mm?
 
18mm is 18mm and 50mm is 50mm, regardless of DX or full frame.

The 18-70 will be wider on a full frame camera - on your D90 you see 18mm cropped. But its still 18mm, but with the sides and tops missing.
 
Deep breath....

The lens is always what it is, a 50mm lens is always a 50mm lens but you get a different effect depending upon the size of the sensor.

Lenses are always described as their own length and not as the effective length on a particular sensor. So, a 50mm lens is always described as 50mm and not as 75mm which is what it appears to be when fitted to an APS-C camera.

All lenses fitted to an individual camera will be subject to the effect the sensor creates so a 50mm lens will give the effect of a 75mm lens on an APS-C camera and the effect of a 50mm lens on a full frame camera. Stick a 50mm lens on a FF camera and it'll be 50mm, but it'll look like 33mm on APS-C.


So, a 50mm lens mounted on your camera will give the same field of view as a 18-105mm lens mounted on your camera and set at 50mm, but in effect 50mm on either lens on an APS-C camera will look like 75mm on FF.

To get the FF effect of 50mm on an APS-C you need something like 33mm.

I hope that makes sense.
:)
 
woof woof said:
So, a 50mm lens mounted on your camera will give the same field of view as a 18-105mm lens mounted on your camera and set at 50mm, but in effect 50mm on either lens on an APS-C camera will look like 75mm on FF.

:)
Click to expand...

Perfect, that was the bit I was after!!

I fully understand that 18mm is 18mm no matter what etc, it was more a 'if i look throught the view finder with 50mm prime on, is it going to look the same as my dx18-105 at 50mm given that it's a DX lens that if used on a full frame camera ends up cropped'.

Cheers! :thumbs:
 
Yup.

I think you've got it. Lenses are always described as what they are and the sensor size decides the effect of all lenses mounted on it.
 
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