Nikon DX offset sensor

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Now I am going to try the membership out here and see who just jumps and who tests before opening there mouth.
I have had all the Nikon DX from D50 to D7100 and they are all the same.
Put a circle in front of the lens (discovered this on a fisheye) and the circle does not come out central on the frame.
The photo below is of a 67-28mm reducer screwed onto the 18-140 lens....On my screen there is a 13mm gap at the top and 8mm at the bottom.

So the sensor is not aligned with the optical axis but about 1.5mm down...So why?

If you are a non beleiver try it
 
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Does not seem to be lens dependent ..just put a central hole in front of the lens (or a fisheye) to get the effect ...anything from D50 onwards ... you bulld a filter for the lens and you have to offset it.
 
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Canon's crop bodies used to be the same but it may have changed (I haven't had any for the last x generations). Is it not to allow for the thickness of the mirror and sub-mirror in the stowed position?

Bob
 
Well bob its nice to have a sensible reply on this forum and no abuse by people calling me an idiot ...on Canon as well. I did suspect it was a design feature to reduce the size of the mirror box and hence camera. I tried the same fisheye on my D800 and its central . No boubt this is because of the film origins of the FX bodies.
So folks if you are using a fisheye or making misty filters for your lens remember if its DX its a little offset from the centre.
 
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A typical FF lens produces a 44mm image circle at the register distance (TS-E, PC-E lenses are much larger by necessity) and there's very little redundancy as the sensor/film needs 43+mm for full coverage. Canon's APS-C needs 26.7mm to cover the sensor but the same lenses can also be used on some of their video cameras and these need 28.2mm to cater for the 16:9 aspect ratio. Hence on the crop 3:2 aspect ratio sensors of the crop bodied stills cameras they had a little latitude on placement.
I've no idea of Nikon's motives for doing the same but perhaps a similar situation.

Bob
 
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