DX / FX Lenses .....Huh???

[Changedsoul]

So I have been reading about getting a new lens. learning about the difference between the DX format and the 1.5x size diff. But what I cant seem to find is info on what it applies...for example.

My camera (Nikon D90) came with a AF-S Nikkor 18-105mm DX lens. When I set the zoom lens to around 24mm and look through the view finder, I find this seems to be the range I generally shoot at. My question is this, since this is labeled as a DX lens, does it mean the values are 35mm Equivalent?

I know if I place a 24mm lens on my DX body it will effectively show an area of a 35mm lens on an FX Body? Am I correct on this? If I am, what is the difference if the lens I attach is labeled as a DX lens?

I just dont want to use my zoom lens focal length as a guide to buy a prime in the range I shoot. Since it seems to be 24mm, I dont want to buy a 24mm NON DX style lens and attach it only to find I am now shooting at 35mm.

Did I explain myself clear enough?

[Franglais]

You have clearly described - a common misconception about DX and FX lenses. There is no tricky difference between them except for the size of the image circle drawn by the lens on the sensor:

- an FX lens makes a big image which covers both FX and the smaller DX sensor
- a DX lens makes a smaller image which only covers the DX sensor

If you put a 24mm FX lens on your D90 then the 18-105 DX set at 24mm you would see no difference.

If you put the same lenses on a FX format body then you would see that the 18-105 DX image is dark or even black around the edges. It isn't designed to provide an image to cover the bigger sensor.

[Changedsoul]

Thanks for the quick response. So just to see if I understand this correctly, me having a DX camera, i can pick either a DX lens or an FX lens and see no difference. But if I had an FX camera, I do not have this luxury because a DX lens on a FX camera will not fill the whole sensor area?

But if an FX draws a bigger circle, would not a 24mm fx lens cover 1.5x the image area of a DX and so the DX camera with an FX lens would only see a portion of the 24mm?

[volks]

Charles explained quite well.
Maybe this will help as well...

Nikon DX Format Cameras

[volks]

Changedsoul, you might find this interesting as well...

Nikon DX vs FX

[Franglais]

CS>> So just to see if I understand this correctly, me having a DX camera, i can pick either a DX lens or an FX lens and see no difference. But if I had an FX camera, I do not have this luxury because a DX lens on a FX camera will not fill the whole sensor area?

>> Exactly. However I believe that if you put a DX lens on a FX camera like the D3 the camera automatically uses only the central part of the sensor corresponding to the DX format and puts a rectangle around it in the viewfinder.

CS>> But if an FX draws a bigger circle, would not a 24mm fx lens cover 1.5x the image area of a DX and so the DX camera with an FX lens would only see a portion of the 24mm?

>> Yes. Put an FX lens on a DX body and there is a wide area inside camera body around the sensor illuminated by unused parts of the image.

[Changedsoul]

Thanks for the links. It was some good reading. I clears some questions up, but still a bit confused. In the end, having a DX camera, do i have the luxury of picking between DX and FX lenses with no change in field of view?

[Franglais]

... In the end, having a DX camera, do i have the luxury of picking between DX and FX lenses with no change in field of view?

Yes. I have a mixture of DX and FX lenses and I use whatever is most suited with my D300 (DX sensor)

For instance the next time I follow a studio nude course I am going to use:

- the 40mm DX macro because it has the best definition of all my lenses
- my 28-70 f2.8 FX zoom because I know that at one point I must do a shot from a precise point and the 40mm is too telephoto. The 28-70 can do 40mm of course but it can also go wider. In fact I may just take the 28-70, that's what I did last time

[wfooshee]

The focal length equivalence does not change by the lens, but by the camera sensor size.

DX or FX lens produces the same image on a DX camera.

But if you compare shots with someone using an FX camera, that's when the same focal length yields a different image in the frame. FX camera at 24mm is a wider angle shot than a DX camera at 24mm, because the FX sensor is larger.

Reminds me of comparing the 35mm SLR to a medium-format camera back in the day. A "normal" lens on a 35mm would be a 50mm lens, but you'd need an 80mm lens to get the same image on a medium format camera.

Basically, the larger the image you're producing at the focal plane, the longer focal length you need from the lens. But if you're not changing the image size, then you don't have to "recalculate" the focal length to get to something you're familiar with already.