Firstly, my apologies -- this is a pretty awful shot, especially given the equipment I was using!
A couple of weeks ago, during one of my many trips to try and photograph Vancouver's temperature inversion (of which prints from my successful trip are now available to purchase, see the bottom of my profile for details ;) ), I met Michael, a fellow photographer who lives in North Vancouver.
After chatting for a while as photographers are prone to do, I showed him some of my star photos, and he was very interested in learning more. So last night, we headed up to Porteau Cove to see what we could get.
Unfortunately, the Pacific Northwest weather conspired against us, and it was a total washout, with 100% cloud cover. So as to at least take some photos, we stopped at an overpass on the way home to take some shots of the Trans-Canada Highway.
It was a Sunday night, so there wasn't much traffic, and it was not the most inspiring location (no background interest, unlike my Seattle photo from a couple of days ago). In most cases, the photos from such a shoot would go from my memory card to the computer, be quickly checked to see that they were, indeed, nothing special, and then be consigned to my storage drive, probably never to be looked at again. (I do this quite a lot).
However, Michael owns rather a lot of rather nice equipment (such as a D800E *and* a 5D Mark III, along with top-end lenses for both, a Gigapan Pro, and so on -- pretty much everything I could dream of having one day!). So when he pulled out his Canon 17mm tilt-shift lens and asked if I wanted to try it out, what could I say?
I've read about tilt-shift lenses. I understand what they're used for, how they work, and so on. But I've never even seen one in real life. So unsurprisingly, getting the most out of it was probably not going to happen -- and it wasn't the best location for tilt-shift photography either. But after some fiddling, I managed to set it up to isolate a narrow strip of the road, which presents quite an unusual effect similar to how an old large-format camera might look (or an Instagram filter -- sigh). I bumped up the ISO to capture some cars without too much motion, as this showed off the tilt-shift effect reasonably well.
As I say, absolutely nothing special, but it was a thrill to use such an unusual and desirable lens, even with only mediocre results. And many thanks to Michael for happily handing over a $2,500 lens to a guy he'd only known for about an hour. Especially as a tilt-shift lens has numerous levers and locks to twiddle, so it'll probably take him 15 minutes to get it back to normal. And because it has a front element that will scratch if you even look at it sharply:
http://upload.wikimedia.org/wikipedia/commons/5/59/TS-E_17mm_f4L.jpg
There's an excellent review of the lens here which shows what you can do with it -- it's a bit technical in the first half, but there are some good examples starting about half-way down:
http://www.the-digital-picture.com/Reviews/Canon-TS-E-17mm-f-4-L-Tilt-Shift-Lens-Review.aspx
And also as you say, Photoshop, and especially CS6 and Camera Raw 7.0 handle all of the perspective corrections you could ever want, and provide flexibility of choices so easily that you could never get at a shoot. The issue people find, I guess, is that people often don't know what they will need to process as they are taking their shots, so the shots themselves are not sufficient enough to correct! The classic example is the "leaning and converging verticals" problem when shooting upwards, big architecture is a common situation. You just have to leave extra breathing room at the top and upper sides of the frame to "expand into and extra "wide angle" stuff at the bottom (sides especially but also the bottom of the frame) that will get squeezed out as the perspective is altered.
The only possible use I see is to provide ultra-wide DOF at super-wide apertures, especially to keep ISO low in low-light conditions. Just about everything you can fix in an editor, but DOF and motion-blur are two you just can't, and significant noise reduction just screws up sharpness to boot.
You shouldn't need to use manual exposure for a tilt-shift lens -- as all the manipulation is done in-lens, you should get an accurate reading from the camera's metering system. Of course, in some situations (such as stitching together images from different extremes of shift) you will benefit from manual exposure, but no more so than when stitching images from a normal lens.
You do have to manually focus the lens, but with live view that's nowhere near as problematic as it used to be. It means you probably will be using the lens on a tripod, but that's pretty much a given for architectural work anyway. I use manual focus for all my tripod-mounted shots anyway (which is almost all my shots) and manual exposure for my night shots.
The main benefit of a tilt-shift lens over Photoshop manipulation is sharpness. When you correct perspective in Photoshop, you are stretching the pixels -- with significant correction you can be stretching pixels at one edge of the image to be twice as big, halving (or worse) resolution. Not a big deal when posting on the 'net, but if you do prints, it becomes quite noticeable.
The same applies when using tilting to alter the focal plane -- you can shoot at f/22 or higher with a normal lens to get everything in focus instead, but APS-C format DSLRs (and crazy-resolution full-frame cameras like the D800) start to lose resolution due to diffraction over around f/11, so again you will have a (relatively) very soft image. With a tilt-shift lens, you can avoid that resolution loss.
It's certainly a lens on my list of things to buy (in an ideal world), but probably after a 14mm f/2.8 and 24mm f/1.4 (for stars), a super-telephoto that gets sharp before f/11, a macro lens, a fisheye, an 85mm f/1.2...
As for the "sharpness" of perspective correction in Photoshop, I have no reference other than CS6. but rely on opinions of writers like Ben Long and Scott Kelby. Yes I know Scott is in Adobe's pocket, but still... Even with my novice eyes, adjustment in Camera Raw 7.0 Lens Correction appears significantly better than in Photoshop Filters | Lens Correction. Apparently stuff in Camera Raw (and Lightroom I guess) haven't made it back into Photoshop in this area. And perhaps never will, according to commentators about the future direction of Photoshop like Steve Johnson. Business as usual at Adobe.