The Canon EF 85mm f/1.8 II USM lens is a moderate weight (15 oz), very well built lens. It does not come with the appropriate hood, the Canon ET-65 III. You get both a lens cap and a mount cap, all packed inside tight conformal foam to protect the lens during shipping. There's also a very brief manual and the usual warranty paperwork.
The lens offers AF and manual focus, and allows manual focus even when AF is set to on, a very useful feature for low-light and other challenging focus situations. This is a USM lens, and as a direct consequence focus is fast and precise, just as you'd expect.
The AF/Manual switch is in a reasonable location, close to the camera body. There is a range indication on the barrel of the lens behind a transparent window which serves to keep dust and debris out of the workings of the lens. Manual focus is controlled with a broad, easy to manage textured ring about mid-body on the lens. During focus, nothing external on the lens body moves or rotates, so there are no complications for using polarizing filters, and no concerns about the lens "pumping" air and so causing dust contamination in either the lens or camera with use.
The lens lacks any form of image stabilization. IS is showing up in more and more lenses, though for the price... perhaps this is one of the justifications for building IS into the camera body. I'm sure that this design wouldn't be anywhere near its current price point with IS added to the build. One last point is that since the lens is a fairly fast design, perhaps there is less overall need for IS (though that argument falls completely apart the first time you *do* need it!)
It takes a 58mm filter, though I highly recommend the use of the ET-65 III hood rather than a filter; filter use should be limited to polarizers, neutral density filters and so on, rather than keeping a filter on the lens with the idea of protecting it. Here's why: filters create a flat surface over the end of the lens that can (and often does) create low-level reflections. These are most apparent in low-light shots, but they are almost always there. In the case of a UV filter, no other benefit is gained (UV can't get through the lens system anyway) other than physical protection. The hood, however, keeps the lens out of harms way quite effectively, and it increases contrast and reduces flare at the same time by preventing light from entering the lens at high angles of attack. I have shot with both hoods and filters, and after decades of experience, I have to come down firmly on the side of hood technique. It only takes one shot ruined by a filter reflection to wake up to this reality; and hoods never, ever compromise an image. They're simply the best way to go. Finally, the hood for this lens is inexpensive, well worth the extra few dollars it costs.
Aperture is controlled by an 8-blade system. The available f-stops range from f/1.8 wide open to f/22.0 fully stopped down. MTF (sharpness) peaks at f/5.6, and vignetting is almost gone by that setting.
On my camera, an EOS 50D, resolution loss from diffraction effects begin at f/7.6, so in many ways, the "sweet spot" for this lens for me lands naturally at f/5.6. On a camera with a lesser sensel density such as the 40D, diffraction doesn't set in until higher f-stops, but you're beginning to lose sharpness from other effects, so I'd still call the sweet spot as f/5.6 (which also provides a fairly extensive depth of field) for shots where detail is the primary consideration.
For portraits, you'll want to go right for f/1.8 if lighting conditions allow in order to take advantage of the shallow and pleasing DOF isolation this lens is famous for; background blur is very soft yet very strong, while the in focus region remains deep enough to keep the important features of the face in focus from ear to nose. The loss of MTF at f/1.8 is noticeable, especially once you get a feel for how the lens performs at f/5.6, but in my opinion, the compromise is perfectly acceptable in a portrait context. There's another benefit as well; at 85mm, and especially on a crop body like the 40D or 50D, this lens allows you to get some distance from your subject which tends to make them more comfortable, while giving you the modest compression that is the hallmark of any telephoto lens. Portraits "pop" and backgrounds blur away with commendable speed. Head-and-shoulders work will put you at about eight feet, and as the lens can focus down to just under three feet, this gives you considerable control over framing without ever running into a limit imposed by the lens design.
This is also a truly excellent lens for not-very-wide field astrophotography, although at critical focus and maximum aperture, chromatic aberration will make itself felt on the brightest stars, which you will then have to compensate for. I have successfully used this lens to capture the the Orion nebula, Andromeda galaxy, Triangulum galaxy, and a number of other astro objects that range from the easy to the difficult, all using no more than a standard (non-tracking) tripod, this lens, and the EOS 50D. On a crop body, 85mm (136mm effective FOV) is definitely the place to be to compromise between star trailing and magnification, and the f/1.8 aperture allows fast enough exposures to eliminate trailing at ISO 1600 and above.
I carry this lens nested in a large camera bag (a Tamrac 5612 Pro 12, *highly* recommended); I rarely put the lens on the camera until I am ready to use it, and when I am done, I take it right back off, cap it, and bag it without wasting any time or motion. I do both the assembly and disassembly "blind" in the bag, using the bag top to shield the camera and lens from the wind and environment as best I can manage. The lens has a raised alignment dot that makes blind assembly practical. It's the size of the overall investment that drives this behavior, of course; both the camera and a lens like this deserves -- demands -- good care and that is just what I try to provide.
Physically speaking, this lens isn't as large as you might think. Canon did a great job of packing a lot of glass (nine elements in seven groups) into a decent form factor of 3" diameter by 2.8" long; even with the hood mounted, this lens provides a fraction of the intimidation factor of, for instance, the 70-200mm f/2.8L. But at 85mm, it can still "get in there" and catch a lot of action without forcing you to crop to extremes. It's light enough that you can shoot for quite a while before fatigue sets in, an issue that will rear its head in any situation that goes on a while, like a wedding or a play (and that low-light capability is great for stage work, where a flash annoys literally everyone.) Plus it is black, and so looks more like it is designed as part of the same camera system, unlike the L's with the white bodies. That's also less distracting in a dark theater.
I can honestly say that this is definitely one of my favorite lenses. I have a fair collection of primes to compare it to, some of which are L glass, and I've got some great L zooms as well; yet for portraits, I inevitably turn to this specific lens as it outperforms everything else I own in the successful shooting methodologies I find myself returning to over and over. Frankly, at the price, I think it is perfectly fair to characterize this lens as a "must-have"; if you're ever going to shoot a portrait, trust me, this is the lens you want (even over the 85mm f/1.2L, which has far too narrow a depth of field for most reasonable portraiture, though you can't beat it for light-gathering.) Like Canon's 100mm f/2.8 macro lens, the 85mm f/1.8 is one of those where you're left scratching your head as to why it doesn't have an "L" designation. It is an outstanding performer.
If Canon were to re-do this lens, I'd like to see them add image stabilization, and perhaps some modern anti-CA elements, as this is the one area where this lens occasionally bites the photographer in high-contrast situations. Until that day, though, this lens is unmatched by anything else in Canon's line for price/performance, and I can't imagine anyone ever regretting its purchase.