Macro on DX or FX

Geoffc

Senior Member
I'm normally OK at this sort of thing but my brain isn't working today so here goes. My wife has a 90mm macro that she use on her D300. If she fills the frame with whatever she is shooting it will be a 12mp image with associated resolution. If I put this DX lens on my D800 or a D7000 for that matter and take the same picture, the subject is now a 16mp image approx. The latter gives better resolution.

I got it into my head that if I buy a 105 Nikkor FX Macro I can then fill my 36mp frame with the same image give or take the difference between 90 and 105mm. I'm now thinking this is not the case as a 1:1 image is x mm wide on the sensor regardless of the sensor size. Therefore if I photograph something small I will have a lot of space around it on FX compared to DX. For example, if I take a picture of something 23mm wide it will fill a DX frame but leave lots of space around an FX frame. If I shoot something 35mm wide I will fill my FX frame but cannot fit it on my DX frame at 1:1.

Shall I just have a lie down?
 

Marcel

Happily retired
Staff member
Super Mod
Why not try your wife's 90 on your D800, do the same shot with your 7000 and compare your results?
 

WayneF

Senior Member
I got it into my head that if I buy a 105 Nikkor FX Macro I can then fill my 36mp frame with the same image give or take the difference between 90 and 105mm. I'm now thinking this is not the case as a 1:1 image is x mm wide on the sensor regardless of the sensor size. Therefore if I photograph something small I will have a lot of space around it on FX compared to DX. For example, if I take a picture of something 23mm wide it will fill a DX frame but leave lots of space around an FX frame. If I shoot something 35mm wide I will fill my FX frame but cannot fit it on my DX frame at 1:1.

Shall I just have a lie down?


You are right, but there are three ways to look at it.

1. With a regular lens in a regular scene (with the subject several or many feet distant), trying two lens on same body, from standing in the same location - the longer lens has a telephoto effect, a magnification that is proportional to the focal length (the 100 mm lens image will appear twice as close and large as a 50 mm lens). The shorter lens is wide angle, in comparison.

2. With the same one lens on two FX and DX cameras, from standing in the same location (several feet), the FX sensor is larger, and so larger simply will show a wider view, more width - from the same lens. The FX and DX image subjects are shown same size (same lens), however when both images are enlarged to the same print size, the FX subject objects will appear smaller. The FX image was NOT smaller (it was the same lens), but the smaller DX frame and view simply must be enlarged more, simulating a telephoto effect, looks closer and larger. See FX - DX Lens Crop Factor

3. With Macro at extreme close up, say for 1:1 (in either of two lenses, or in FX and DX bodies), then 1:1 is still 1:1. 1:1 is NOT about the frame size, but the 1:1 image size is the same size as the actual subject. But to achieve the same view (width), the DX camera has to stand back more because it is effectively 1.5x longer focal length (if same lens, but simply because of the greater enlargement of its smaller sensor to get the same image) Or - to achieve 1:1, either body will have stand at about 6 inches distance with 105mm lens, instead of maybe 2 inches with 60mm macro lens (working distance, in front of lens). Both are a 1:1 size image (but FX will show a wider view). So with macro, you do not stand in the same place to compare.
 
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