DX lenses

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essahar

New member
Hello,

I just have a small question for normal or FX compatible nikon lenses to have the focal length for DX body is to multiply what is written on the lens by 1.5 for example the 70-300 will equivalent to 105-450. Does this apply to DX lenses too? Or what it's mentioned is the real focal length

Thank you


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Marcel

Marcel

Happily retired
Staff member
Super Mod
Yes and Yes.

The actual focal length will not change, but the field of view will. The DX just crops the image before hand so you see less in the picture. It's basically just cutting the image all around by a factor of 1.5.

Welcome to Nikonites.
 
BackdoorArts

BackdoorArts

Senior Member
As Marcel stated, all lenses, whether DX or Full Frame, have focal lengths listed based on the 35mm standard. When they are placed on camera body the effective focal length is determined by multiplying by the sensor crop factor, which as you stated is 1.5 on Nikon DX bodies, as well as on Sony and Pentax. Canon uses a 1.6 crop factor, and Olympus sensors have a 2.0 crop.
 
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aroy

Senior Member
The focal length mentioned in any lense is always real. What differs with the sensor size is the Field of View - FOV. As DX sensor is shorter, about 24mm long verses 36mm for the FX sensor, image gets cropped. So you get a cropped image with respect to FX sensor, hence the FOV is less, as though the lens focal length was more. So in effect what you see with a 300mm lens in a DX sensor is the FOV that would have been in a 300x1.5=450mm lens on an FX sensor.

OT.
If the sensor is half the length, that is 18mm instead of 36mm, then the crop would be even more and the FOV would be same as a lens with double the focal length.

What makes the DX more interesting is when you have the same MP in both DX and FX, say D7100 and D610. Here the DX sensor has more resolution (pixels/mm of image), so if your image is small, say half the sensor width - 12mm, then the DX image will have more resolution, that is why for wild life, where the animal/bird rarely fills up the frame DX, will have more resolution, but at the expense of higher noise.
 
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Steve B

Senior Member
One other important factor is what sensor size a lens is designed for. While a 50mm lens is a 50mm lens no matter what the sensor size is, a DX lens creates a smaller image circle at the sensor plane than an FX lens.
 
Bob Blaylock

Bob Blaylock

Senior Member
essahar said:
Hello,

I just have a small question for normal or FX compatible nikon lenses to have the focal length for DX body is to multiply what is written on the lens by 1.5 for example the 70-300 will equivalent to 105-450. Does this apply to DX lenses too? Or what it's mentioned is the real focal length
Click to expand...

The focal length is real. The confusion has to do with the size of the frame, be it a frame of stone-aged 35mm film, some other format of film, or the sensor in a digital camera.

For a very long time, 35mm was the very most common film format, with a standard frame size roughly 36mm by 24mm. A lens with a 50mm focal length was considered the “standard” size lens to use with a 35mm camera, because it yields an angle of view that is roughly comparable to that of the human eye.

FX-format digital cameras use a sensor that is about the same size as a standard 35mm film frame, so a lens used on an FX camera will have the same field of view as that same lens on a 35mm film camera.

DX-format cameras use a sensor that is smaller than a 35mm film frame. The same lens used on a DX-format camera will have a narrower angle of view, than on an FX-format camera.

An FX-format sensor is roughly 1.5 times the size of a DX-format sensor. This 1.5 is the “crop factor” you've heard about. Since a DX-format sensor is 1.5 times smaller than an FX-format sensor, you need a lens with a focal length 1.5 times shorter to get the same angle of view on a DX-format camera compared to an FX-format camera. While 50mm is considered the “standard” focal length for a lens on an FX-format camera, the “standard” lens for a DX-format camera would be around 35mm.

See also:
600px-Crop_Factor.JPG 595px-Full-frame_vs_APS-C.svg.png
550px-Sensor_sizes_overlaid_inside.svg.png

The only real difference between a DX lens and an FX lens is that an FX lens is expected to be used on a FX-format camera, or a full-sized 35mm film camera, and so needs to project an image that will cover a full 35mm-sized frame; while a DX-lens is expected to only be used on a DX-format camera, and is only expected to cover a DX-sized frame. You can use an FX lens on a DX camera with no issues, but if you use a DX lens on an FX camera, it won't cover the entire frame.
 
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essahar

New member
Thank you for your help

DX lenses can be mounted on a full frame body but it will act as a cropped sensor so it make sense that for these type of gears the focal length mentioned is in cropped sensor size.

That's not true


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