Would you buy a specific type of camera body just to accommodate one particular lens?

It's a pretty sure bet that I would. My recent re-fascination with owning a full frame Nikon camera started innocently enough, I'd purchased a D7100 (APS-C frame) and just for fun I took a gander at the used, manual focus Nikon lens case at Precision Camera. My eyes locked onto two lenses that I wanted to add to my meager, existing collection of good Nikon vintage glassware. I own the Nikon 50mm 1:1.2 ais lens and find it to be pretty remarkable when I stop it down just a tad. I couldn't resist the pricing on two very clean brothers to that lens, the 55mm f2.8 Micro-Nikkor ais lens and the amazing and wonderful, 105mm f2.5 ais lens. These are both well made lenses that were built in the 1970's and 1980's when it was assumed that a lens would be made from metals that worked well together to reduce friction coefficients and to expand and contract, in concert, with heat and cold. Everything about the lenses is industrial strength and there are no small, electronic parts that will eventually fail and be impossible to replace. The glass on both lenses was/is immaculate and the focusing smooth through the entire focusing rack. 

I owned both of these lenses when I shot with the system in the film days and had always assumed (incorrectly) that they had been superseded by more modern designs and manufacturing methods. But the reality is that the lens companies have learned more how to fudge tolerances and assembly variances than they have learned better ways to design lenses for ultimate quality. Most companies still depend on very classic designs and  the makers use ED and aspheric elements to compensate for the necessary slop required to cost effectively mass produce products in large numbers, without hand adjustments. 

The last 105mm Nikon lens I owned was the 105mm f2.0 DC (or "defocus coupling") lens. It's outrageously good and it's the lens I used to make the three images (one above and two below) for the Austin Lyric Opera for an ad campaign years ago. I used the good camera of the time, a Kodak DCS 760 which was not full frame but it was closer than APS-C as it had a 1.3x crop factor. 

Once I bought the (under $200) 105mm 2.5 ais back a few months ago I put it on a D7100 and did a few tests. When the lens was stopped down to f4.0 it was very sharp across the frame. At f5.6 it was brilliant. But more importantly I really liked the very subtle transitions this lens made in tones and the graceful way the focus falls off. It must be one of the "bokeh lenses" that people discuss with such rapture. When I compared it to modern lenses there was a difference not in sharpness or resolution but in contrast and tonal transfers (the gradation from one tone to the next) that made this lens seem much more appropriate to me for current portrait work. The only issue was the focal length; it's a bit too long for a smaller frame and an even smaller studio. 

That was the slow motion rock slide of ideas that started pushing me toward getting some sort of full frame Nikon mount camera. I wanted badly to use this lens especially, but also the 50mm f1.1:2 at the angles of view for which they were designed. Didn't really matter to me which modern body to get as long as it used the right sized sensor to give me back those two focal lengths that I enjoyed using in "the good old days."

Well, after waiting all day for the post man to arrive the D610 I bought landed in the office. I went through and quickly adjusted all the menu items which was simple as they are largely (almost completely) identical to those of the D7100 and the D7000 before it. The first lens I put on was the 105mm f2.5. I plugged in the focal length and maximum aperture information to the camera and shot some test frames. The long focal lengths and fast aperture actually helped me achieve good focus manually and when I framed a few shots I was in my visual happy place. Two lenses make FF fun and situationally desirable: the classic 50mm and the classic 100-105. In third place is that in between focal length, the 85mm. Now I need to e-mail some of my favorite models and do some fun, studio portrait tests. Fadya, if you are reading this......

Below is a shot of the grumpy photographer/writer/editor of this site. What a serious looking guy. This must have been during the years in which he did not own a Nikon 105mm f2.5 ais lens......

Make him smile ( a little ). Buy a Kindle copy of his 

Novel...