It's not the 85mm f/1.4 AIS. While a legend in it's own right, it just didn't compete with the magic of the 135mm f/2 AIS. I didn't give a second thought to selling my 85mm f/1.4 AIS--the 135mm f/2 AIS was just that much better. Besides, I still have my Polar 85mm f/1.4 for when I have a hankering for that focal length.
It's also not the 20mm f/4, whose prices have recently commanded astronomical sums. While it was a fun lens to play around with, it just wasn't as nice as my 20-35 f/2.8 @ 20mm. Heck, I could barely tell the difference between the 20mm f/4 and the much cheaper Vivitar 19mm f/3.8.
It's not any of the zooms I've owned either.
The lens that I regretted selling was my 50mm f/1.8 AIS MKII. It looks like the Series E, but it's not. It's housed in a completely metal body, and has the same optical formula as the E, but with NIC coatings. It was made exclusively for the Japanese market, so it's a rare bird to find on this side of the world. It's also a very fun lens to use. All of my bee pictures from my first summer with them were taken with that lens and some old-school extension tubes. Will I be using it for macro work? No. The 55mm f/3.5 is a far better tool. I bought it mainly because I missed it and because it makes street shooting that much more discreet with the D700.
While its optical prowess may be lacking when compared to the gelded 50's, I'm not so gullible as to believe that photography is all about the latest and the greatest. Sometimes old-school tech is just so much more fun because it lets you be more in control. Besides, there's just a charm due to its size and build-quality that can't be beat by today's plastic wonders.
This is the second time I've owned a 50mm f/1.8 MKII and this one's staying in my arsenal for good. I purchased it from Japan and it took but 4 days to reach me. I have no idea how that happened, but typically EMS shipping from Japan to the mid-west takes about 10 days. I'm not complaining. The lens I received looked brand new, like it hadn't even been used and there was little dust between the elements. An amazing and rare thing to come across considering how rare this lens has become and how rare this lens is on this side of the world.
I can't wait to take pictures with it!