DX crop factor

[Adroit]

I hope this question hasn't been answered (oh well, I'm sure it has, but I can't think of a good search string to find it).

I own a D300 with an 18-200 zoom, which of course is a DX lens. My questions is, is the 18-200mm focal range relative to the DX sized sensor, or a medium format 35mm sensor?

Another way of phrasing it; if I zoomed all the way to 200mm with my 18-200 DX on my D300, and then zoomed all the way to 200mm with a 70-200 FX lens attached to a D3, would I see the same level of zoom on both cameras, or would the D300 appear to be further zoomed in because of the crop factor?

 

[Solarflare]

The FX chip is ~36x24mm.

The DX chip is ~24x18mm, i.e. half of the surface area. Meaning the width and height are 75% of the FX chip and the diagonal is about 70%.

So if you use a DX camera with the 28-300mm FX zoom, it should be approximately (not precisely though) the same as the 18-200mm DX zoom.

Using a FX camera with a DX lens though makes no sense. I think the FX camera will simply switch to a DX resolution, i.e. use on the the central half of the fotochip surface.

 

[o hey tyler]

The D300 would have narrower field of view at 200mm than a D3.

Also, Medium format is much larger than full frame 35mm.

 

[Solarflare]

Haha missed that.

Yes medium format is *looks it up* 50x60mm.

 

[Adroit]

So regardless of whether a lens is DX or FX, the field of view is the same?

And thanks for correcting me on medium format - I thought it was 35mm!

 

[Alan92RTTT]

Another way of phrasing it; if I zoomed all the way to 200mm with my 18-200 DX on my D300, and then zoomed all the way to 200mm with a 70-200 FX lens attached to a D3, would I see the same level of zoom on both cameras, or would the D300 appear to be further zoomed in because of the crop factor?

The D300 is a DX sensor camera so it would give you a longer effective length.

Lenses are always marked on the same scale regardless if they are made for DX or FX cameras. So any lens you attach to the D300 would give you and image with an effective zoom of 1.5~ times the rated number.

 

[Solarflare]

Sorry, correction to my above computations: of course the DX/APS-C format is 3:2 just like FX/Fullframe, so its ~24x16mm, not ~24x18mm (a bit smaller than that).

Which means its more like 45% of the surface of the FX fotochips, and its about 2/3 of the width, height, and diagonal.

 

[mjhoward]

So regardless of whether a lens is DX or FX, the field of view is the same?

No, regardless of the format the FOCAL LENGTH is the same. It is a property of the lens, not the system. The field of view for a given focal length may be different for each format.

 

[Trever1t]

Another way of phrasing it; if I zoomed all the way to 200mm with my 18-200 DX on my D300, and then zoomed all the way to 200mm with a 70-200 FX lens attached to a D3, would I see the same level of zoom on both cameras, or would the D300 appear to be further zoomed in because of the crop factor?

The D300 is a DX sensor camera so it would give you a longer effective length.

Lenses are always marked on the same scale regardless if they are made for DX or FX cameras. So any lens you attach to the D300 would give you and image with an effective zoom of 1.5~ times the rated number.

This is incorrect.

The FOV is cropped but the focal length is not affected. a 50mm is not 75mm on a Nikon DX body but the Field of View is that of a 75mm, meaning narrower. This seems to be a very difficult thing for people to comprehend!

 

[kundalini]

...I own a D300 with an 18-200 zoom...

Ignore the math. You have a zoom lens with a focal length from 18mm to 200mm. If you have never shot with larger format, the crop factor is irrelavent and you will not know any difference.

 

[Alan92RTTT]

Another way of phrasing it; if I zoomed all the way to 200mm with my 18-200 DX on my D300, and then zoomed all the way to 200mm with a 70-200 FX lens attached to a D3, would I see the same level of zoom on both cameras, or would the D300 appear to be further zoomed in because of the crop factor?

The D300 is a DX sensor camera so it would give you a longer effective length.

Lenses are always marked on the same scale regardless if they are made for DX or FX cameras. So any lens you attach to the D300 would give you and image with an effective zoom of 1.5~ times the rated number.

This is incorrect.

The FOV is cropped but the focal length is not affected. a 50mm is not 75mm on a Nikon DX body but the Field of View is that of a 75mm, meaning narrower. This seems to be a very difficult thing for people to comprehend!

You are splitting hairs on a technicality. Pick your favorite way of saying it what matters is the result. A 50mm lens on a DX camera will give you basically the same image as a 75mm lens on a FX camera. Wither its a change in FOV or zoom is irrelevant. All that matter is the images will be similar identical. As the owner of a DX body that what I care about.

I could always use the terminology that flicks uses "Focal Length (35mm format)"

 

[Alan92RTTT]

...I own a D300 with an 18-200 zoom...

Ignore the math. You have a zoom lens with a focal length from 18mm to 200mm. If you have never shot with larger format, the crop factor is irrelavent and you will not know any difference.

From a usage standpoint you are correct.

But, If I see a picture someone took with a D3 and a XXmm lens and I want to be able to take a similar shot I need to convert. Say for example I see a pic from a D3 with a 50mm prime. If I put that 50mm on my D5000 I'll need a lot more working room to get similar framing. Knowing that their is a difference and what it is I can then consider other lenses and that might lead me to the 35mm prime rather then the 50mm (which is why I got the 35mm ).

 

[mjhoward]

A 50mm lens on a DX camera will give you basically the same image as a 75mm lens on a FX camera. Wither its a change in FOV or zoom is irrelevant. All that matter is the images will be similar identical. As the owner of a DX body that what I care about.

Actually it is quite relevant. A 50mm lens on a DX body will not necessarily produce the same image as a 75mm lens on a FX body. FOV isn't the only difference. Perspective Distortion and DOF are a couple of things that come to mind.

 

[Trever1t]

you're not getting closer, you're only using less frame.

 

[KenJulio]

As Trever1t has stated, on a FX body at 200mm, it would be the approx equivalent of 135mm on a DX body.

The designation of DX on a lens only refers to it should be utilized on a DX body otherwise on a FX body, there will be a strong vignette.