I didn’t know that programs like Lightroom can actually compensate based on known lenses – does it also take into account the focal length used in the shot?Yes. And if for some particular shot you feel that it is over-correcting (or if you would have liked some vignetting intact), you can use a slider to decrease or increase the correction - but I've not had to move any slider away from 100% (100% of the lens profile correction) for any of my test shots yet.
Historically I haven’t seriously considered 3rd party lenses, I read several that made it sound like getting a good lens from them is pretty much rolling the dice. I see though I have more than one recommendation, perhaps I should seriously consider this as the prices are better.I just got it (the Tamron 17-50 f/2.8 DI II non-VC) and I'm happy with it so far. I, too, have been sceptical of third-party lenses - I'm extra cautious of their image quality. But for this particular Tamron lens, the IQ is decent - as decent as some very good Canon (non-L) lenses. Of course it's a bit of a compromise, but in this case for 500eu (63%) less money than the Canon 17-55 f/2.8, it was very well worth it (for me).
The compromise for this lens is the noisy AF (but it's fast) and the inverted zoom ring direction (Canon 'zooms' counter-clockwise, while this Tamron zooms clockwise); and of course, it lacks IS (Tamron has a stabilized "VC" version of this lens as well, but its image quality is very bad). The AF noise and zoom direction I'm not at all bothered with (as long as the zoom is quick and accurate), and the lack of IS was worth the savings to me.
Out of curiosity how is the resale value of the Tamrons? Would it be compatible with a future full frame camera or would I need to sell it?Not sure about the resale values, but I assume that it'll be fair, as it's a nice wide aperture (f/2.8 ) lens that's probably about as cheap as it can get for such good sharpness in that range. This lens isn't compatible with full frame cameras though. In fact, vignetting is noticable on the crop camera, especially at 17mm (which, according to the-digital-picture.com, is somehow "wider" than Canon's 17mm as well - don't ask). But as said, shooting RAW and using the standard lens correction profile of that lens on all my pictures taken with it, I see none of it in Lightroom.
Hesbehindyou – The 50mm F/1.8 has allowed me to play with indoor photography without a flash for the first time (realizing I’m sacrificing image quality with higher ISO’s) and its been a quite fun. I actually didn’t know that the full frame equivalent would be a thinner depth of field….amazing what you learn!There's a little bit more to it. 50mm on a crop camera will have the same DOF as it will on a full frame camera - if both cameras are at the same distance from the subject. However, that would result in a different framing from both cameras. (Since a crop camera factually 'crops' part of the fullframe image, it cuts off the edges, and so the framing is different. That's why a 24mm lens is wide on a full-frame camera, but narrower on a crop - the crop camera cuts away the wide edges of the image that the lens displays on the sensor. Still, the part of the image that is in focus is just as wide [or narrow] on both cameras - DOF is the same.)
But as explained, using a 50mm lens on a fullframe camera, you will always get a wider picture than on a crop camera. That means that to get the same framing of a subject, you will need to move closer to it with a full-frame camera. Doing thát will cause your camera to focus closer and increase the relative background distance (blowing it up) - and thát's what creates the reduced DOF and increased background blur from a different camera with the same lens.