rook2c4 Loc: Philadelphia, PA USA

IQ cannot be directly quantified, as it is merely a vague description based upon several factors.

With that aside, if IQ is your main concern, you will be better served buying an old manual F-mount lens, rather than adapting an M42 to the Nikon body. As Nikon's F-mount has a greater focal flange distance than the M42 mount, to achieve infinity focusing, an adapter with correction lens is simply unavoidable. For the cost of an adapter with a really good correction lens, you can just as well find a nice manual lens with the correct mount... plus fully functional auto aperture, accurate distance scale, etc.

Architect1776 Loc: In my mind

They don't to that effect, there is some though with those with elements in them, glassless don't

rehess Loc: South Bend, Indiana, USA

I guess it is time for me to confess that I don't have a Nikon camera. My original reason for asking this question was the occasional Nikon user who is looking for an inexpensive 50mm lens around f/1.4 .... the Super Takumar 50mm f/1.4 had an excellent reputation back in the day. You all have convinced me that was a lousy idea ... are comparable Nikon lenses also reasonably priced?

GoofyNewfie Loc: Kansas City

And it could be radioactive:
https://petapixel.com/2012/10/11/a-look-at-the-radioactivity-of-old-manual-lenses/

Screamin Scott Loc: Marshfield Wi, Baltimore Md, now Dallas Ga

Nikkor 50mm F1.4’s are not exactly cheap unless you can find a bargain as there is a lot more demand. That said, I have both MF and AF iterations. Got the AF version ( 1st iteration of AF) for $35. Don’t expect to find any at that price point though.