I'll get to Canon lenses in a moment, but I wanted to mention a really nice, manual focus telephoto that I think is under the radar for many people. The lens is a Kowa Prominar. On the NX-1 it is amazingly good. The Kowa comes in several mounts, but I think the Nikon mount version makes the most sense as it can be used on many brands with a simple adapter added between the lens and the camera.
I got the lens off eBay from a Japanese dealer. There is a main head unit, which contains 1 fluorite along with 2 extra-low dispersion elements, and a round 9-bladed diaphragm. Between this unit and the camera are 1 of 3 possible tubes ("mount adapters" per Kowa), used one at a time, which create a 350/4, a 500/5.6 or a 850/9.6 telephoto lens. I got the 350 and 500 units. There is no glass in the 500mm tube, but the 350mm tube has several elements (I think the 350mm tube is behaving like a Speed-Booster).
Since the lens breaks into 2 (or 3 or 4 pieces) it fits smaller camera bags unlike most 500mm lenses. And the weight is rather light at 2 kg. Kowa also makes a special fluorine-coated protective filter (95mm) for the main unit.
While the focus is manual, it's very smooth, having both coarse and fine focusing rings. Close focus is 3 m. Using the EVF on the NX-1 together with MF assist makes using the lens easy (easier than using LV on my D810 in bright light; surprisingly, the NX-1 seems to have better resolution that the D810 with this lens).
The results are amazingly sharp. I recently rented the new Nikon 400/2.8 and the Kowa is every bit as sharp and contrasty. However, the Kowa is not f2.8 or autofocus, but then again, it is not as heavy or as expensive (about ¼ the price).
http://www.kowa-prominar.com/product/telephotolens/index.htmlAs for actual Canon lenses, you do not need a fancy electronic adapter for most Canon lenses as long as you're content with manual focus and no IS. For me, this is not an issue as I'm mostly interested in TSE lenses. f-stops can be adjusted easily as I'll describe. Most internet searches will say you need a body with a DOF button. Not true.
I'm in the process of trying my 17 and 24 TSE on the NX-1. I've fixed the lenses at f5.6. But this could even be field adjustable since I have an old, inexpensive Canon (Rebel Gii) film body that I can carry around (uses 123A batteries) that does not have a DOF button (again, not needed).
The process is simple: set desired f-stop in Av (or M) mode, leave cap on lens to trigger a 10 to 30 sec exp and then remove the lens from the body during exposure. f5.6 is fairly reasonable for a crop sensor and not difficult to focus (even the above telephoto is not difficult to focus at f8). Replace lens on the Canon body to either re-set open by taking another exposure, or repeat the above process to set a different f-stop.
While Nikon lenses are often easier to use on other bodies, the 24 PCE, 45 PCE and 85 PCE (except older 85s) all have electronic diaphragms that "cannot" be used on other bodies. Also not true.
Do the same technique on a D series body as on the Canon: adjust f-stop of the PCE lens (manual ring), set to manual exposure for 10 or 20 sec and then remove the lens during the exposure. Now lens is closed down to desired f-stop and you can use on an NX-1 with a basic Nikon adapter (G-type not required). I've done this with a 45 PCE (but did not try it with the borrowed 400/2.8 FE!) Also remember to be careful after removing lens during exposure as the mirror is up until the exposure is completed (maybe immediately place a body cap).