# Nikon DX lens question



## Dave 330i (Jan 4, 2002)

A friend brought up the point that the focal length of DX lens is what is marked on the lens. For example, an 18-55mm DX lens on a DX camera gives the actual focal length on a DX camera. I read the contrary. Regardless of whether a Nikon lens is DX or not, there is always a 1.5 crop factor, even on a DX camera. The reason Nikon came out with the DX lens for DX cameras is they are lighter in weight and smaller in size, therefore, less expensive to make.

Edit: I guess I could satisfy my curiousity by using the same lens on a DX and FX cameras. Anyone want to lend me his D3?


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## PropellerHead (Jan 3, 2002)

Dave 330i said:


> Edit: I guess I could satisfy my curiousity by using the same lens on a DX and FX cameras. Anyone want to lend me his D3?


I think your friend is right. I used the same lens on the D700 and the D300. It was an FX lens, though. When I get home Fri, I'll test on a DX lens for you. You never did answer which 300mm lens you have.


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## Dave 330i (Jan 4, 2002)

PropellerHead said:


> I think your friend is right. I used the same lens on the D700 and the D300. It was an FX lens, though. When I get home Fri, I'll test on a DX lens for you. You never did answer which 300mm lens you have.


AF-S 300mm II f/2.8 mint condition used (not VR). I debated whether the VR was worth $900 more to me, and the answer was no.
http://www.hickingbotham.com/reviews/nikon300200400.htm

FX lens on DX camera will have 1.5 crop. But the question is whether DX lens on DX camera will have the same 1.5 crop. I will compare my DX 18-70mm set at 50mm with my 50mm f1.8 (not DX) later tonight. If both lens give the same size images, then both lens have a 1.5 crop factor on DX cameras. If not, then the 18-70mm set at 50mm will show more.


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## Cliff (Apr 19, 2002)

The focal length doesn't change because of a change in sensor size, but the angle of view captured by the sensor does change. The crop factor is a multiplier applied to the focal length to allow apples-to-apples comparisons across cameras with different sensor sizes. For example my S90 has the equivalent of a 35mm format 28-105 lens, but it's really more like 6-22.5 mm.



Dave 330i said:


> FX lens on DX camera will have 1.5 crop. But the question is whether DX lens on DX camera will have the same 1.5 crop.


Yes. The focal length is an attribute of the lens and it doesn't change. The crop factor is sensor dependent: FF/FX=1, APS-H=1.3, DX=1.5, APS-C=1.6, etc.


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## Dave 330i (Jan 4, 2002)

Cliff said:


> The focal length doesn't change because of a change in sensor size, but the angle of view captured by the sensor does change. The crop factor is a multiplier applied to the focal length to allow apples-to-apples comparisons across cameras with different sensor sizes. For example my S90 has the equivalent of a 35mm format 28-105 lens, but it's really more like 6-22.5 mm.
> 
> Yes. The focal length is an attribute of the lens and it doesn't change. The crop factor is sensor dependent: FF/FX=1, APS-H=1.3, DX=1.5, APS-C=1.6, etc.


The question is whether the focal length markings on the "dedicated" DX 18-70mm is really 18-70mm on a DX camera. If not, the markings would be misleading. Certain, no "pro" would buy a DX lens for the FX camera, even though it would work. I will accept the fact that if you are using a FX lens on a DX camera, you would need to take into account of the 1.5 crop factor.


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## Cliff (Apr 19, 2002)

Dave 330i said:


> The question is whether the focal length markings on the "dedicated" DX 18-70mm is really 18-70mm on a DX camera. If not, the markings would be misleading. Certain, no "pro" would buy a DX lens for the FX camera, even though it would work. I will accept the fact that if you are using a FX lens on a DX camera, you would need to take into account of the 1.5 crop factor.


It is an 18-70 lens no matter what body it is attached to. Now, does it offer the same angle of view on a DX body versus an FX body? The answer is no. Different sensor sizes result in a different angle of view for a given focal length.

A DX lens just produces a smaller image circle than an FX lens, because the area of the sensor it is required to cover with light is smaller. The lens can be physically smaller as a result, although you'd never know that from handling a 17-55DX. That doesn't affect the focal length though.


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## Dave 330i (Jan 4, 2002)

Cliff said:


> It is an 18-70 lens no matter what body it is attached to. Now, does it offer the same angle of view on a DX body versus an FX body? The answer is no. Different sensor sizes result in a different angle of view for a given focal length.
> 
> A DX lens just produces a smaller image circle than an FX lens, because the area of the sensor it is required to cover with light is smaller. The lens can be physically smaller as a result, although you'd never know that from handling a 17-55DX. That doesn't affect the focal length though.


I agree, regardless of whether it is a DX or not DX lens, there will be 1.5 crop on a DX camera. Anyway, the two pics was taken from 50mm f1.8 (left) and 18-70mm set at 50mm (right) on a D90. From those two I would say that the 18-70mm lens on DX camera is cropped because both pictures look the same, and I know the 50mm lens on a DX camera is cropped 1.5. The camera was set on a tripod.


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## SRFast (Sep 3, 2003)

Dave,
If you lived in NYC, I would glady lend you my D3 for a day. 

Regards...JL

BTW, this is SRFast. I have to post using SRFast26 because no one on this site will assist me in resetting my SRFast password.


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## Dave 330i (Jan 4, 2002)

SRFast26 said:


> Dave,
> If you lived in NYC, I would glady lend you my D3 for a day.
> 
> Regards...JL
> ...


Thanks. :thumbup:


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## mathjak107 (Apr 1, 2006)

the lens is always what its marked but for purposes of simplification the field of view changes .

the reason we dont say the focal length changes is the characteristics of that lens stay put such as a portrait taken with a 24mm lens and a dx camera may look the same size and view as a 35mm on a full frame but the 24mm will retain the distortions that a 24mm will have such as making a nose look huge or eye sockets very deep.

the lens in characteristic stays the same regardless for that focal length, its only how wide the view is that changes.


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## Dave 330i (Jan 4, 2002)

mathjak107 said:


> the lens is always what its marked but for purposes of simplification the field of view changes .
> 
> the reason we dont say the focal length changes is the characteristics of that lens stay put such as a portrait taken with a 24mm lens and a dx camera may look the same size and view as a 35mm on a full frame but the 24mm will retain the distortions that a 24mm will have such as making a nose look huge or eye sockets very deep.
> 
> the lens in characteristic stays the same regardless for that focal length, its only how wide the view is that changes.


From reading more about DX lens, I agree. The reason why it is labeled "DX" is because it covers less area since it is designed for the smaller 1.5 cropped sensor, threfore, the lens itself is smaller in diameter, lighter, and cheaper to make.


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## mathjak107 (Apr 1, 2006)

yep.. but the important thing is that the characteristics of that lens be it super wide,wide, normal or telephoto dont change, just the field of view.

ever take a shot with a telephoto taken at a distance vs the same shot up close with a super wide so they are about the same size in view?

the telephoto is very flattened , if its a face you cant tell how long the nose is ,facial features flatten out. the supewide accents all the features making them bigger then life... this is even though they may offer the same field of view.


thats why its not just about field of view being the same.. a 50mm on a dx is very much the same view as a 75mm on full frame but the details in the photo are still different perspectives.


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## Dave 330i (Jan 4, 2002)

mathjak107 said:


> yep.. but the important thing is that the characteristics of that lens be it super wide,wide, normal or telephoto dont change, just the field of view.
> 
> ever take a shot with a telephoto taken at a distance vs the same shot up close with a super wide so they are about the same size in view?
> 
> ...


Interesting. :yikes:


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## mathjak107 (Apr 1, 2006)

it took me a while to figure this all out in my head...but then i realized why the shots looked different even though they were cropped the same size.


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