Why do people say an FX lens 'shines' more on FX than DX

Started Sep 27, 2010 | Discussions thread
MasterOfGoingFaster
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Re: Why do people say an FX lens 'shines' more on FX than DX
In reply to mgblack74, Sep 29, 2010

mgblack74 wrote:

2 reasons. It has to do with pixel pitch (size and spacing of the pixels), and focal length.

Well said. But I should point out, for the OP's sake, that the lens design trade-offs may have a greater influence.

When you design a lens, generally you can choose to have sharpness across the image circle (the area of image projected - your sensor sits here) - OR - design for greater sharpness in the center at the expense of sharpness at the corners. How should you compromise?

In the DX days before FX, it was obvious - take advantage of the smaller sensor size of DX bodies by going for a sharper center and allow the area outside the DX sensor area to go soft. The 70-200mm f/2.8 VR (not VR II) was considered to be a sharp lens. That is - until the D3 FX sensor showed us the area outside the DX area and we saw soft corners. Nikon didn't mark the lens as "DX" but it was clearly not meant for FX cameras.

The 80-200mm f/2.8 was designed in the days of film, so the designer wanted it to be sharp corner-to-corner. The one I used (briefly) was sharper than the 70-200 on FX, but not as sharp on DX.

That Zeiss lens from an old medium format camera may be sharp for a large negative, but may not have enough center sharpness for a DX sensor.

With any lens, you can increase the pixel density to the point that you out-resolve the lens. At that point, you've gone past the point of diminishing returns.

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Ken Elliott
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