Another macro reverse nikkor lens question

zzzxtreme wrote:

Which one should I get that would not give me insane magnification? Maybe something that can focus a (single) 35mm film negative from a distance of under 20cm ?

One of the limits of reversing a lens is that the only way to change magnification is by adding or removing extension or zooming.  To record the full frame of a 35mm negative on a NIkon 1, you would want a magnification of about 0.37x (1/2.7).  Looking at the BR-2A Manual I don't see a prime lens listed which would work, but it looks like a 105mm f/2.5, 135mm f/2.8, or 135mm f/3.5 might come close.  There are several zoom lenses listed which might work as well, but from my experiments with reversing a 35-105mm f/3.5~4.5 I don't think you'll get the quality you are looking for.

Here's another bit of bad news for this approach; my genuine Nikon BR-2A does not lock in properly on my FT-1 (a 30+ year old generic works).  But here's the good news, without using a reversing ring, a 55mm f/2.8 Micro will focus on a 35mm negative at a subject-to-sensor distance of around 200-205mm.  A 40mm f/2.8 DX Micro-Nikkor will also do the job more easily at a shorter subject distance and with metering and either autofocus or focus confirmation.  So too would a Tokina 35mm f/2.8 DX macro, but that's a bit of a scarce lens.

Any help would be greatly appreciated. I'm still confused about relation between crop factor, magnification and focusing distance

Crop factor is irrelevant to magnification or focusing distance.  Magnification decreases with focusing distance at a rate determined by the focal length.