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?
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?