50mm vs 85mm for portraits on a crop sensor?
I've read several times that a 50mm lens will make features like noses noticeably stand out compared to an 85mm lens. However, I'm never sure if the post/article is describing results on a full frame or crop sensor. I know that the longer the focal length, the more the compression to features....because the crop sensor gives a 50mm the effect of a longer focal length, how noticeable is the facial distortion on say, a Canon 550D? I'm considering a prime for portrait work and I'm 'at the crossroads' like all of you who came before me.
I will generally be using the lens for wedding portraits on the beach (and they generally want to get married around sunset, so formal portraits come as I'm losing light — hence wanting a tack sharp f1.8 or below), so it would be handy to have a lens that can take more than just a head/shoulder shot.
Blog to the rescue, check this (this was on a crop sensor) out. And having done much with a 50mm and 85mm - 85mm all the way, but its really just an opinion.
I've been trying to find a way to phrase this exact question. Thanks for doing it far more succintly than I could have.
Quick'n'dirty answer - Neither will distort much at all on an APS-C sensor. The choice is up to personal preferences. If you are shooting such low light though, the bit larger aperture provided by a f/1.4 or f/1.2 over f/1.8 might actually be beneficial.
As a note related to @dpollitt's answer, while you may get an acceptable exposure at f/1.2 or f/1.4, you may find yourself tossing away a lot of properly exposed shots because the depth of field was too shallow and your AF chose the wrong feature to focus on. Example: if shooting at f/1.2 and AF chooses the tip of the nose, the eyes will be out of focus. For me, that can ruin a shot. The standard answer of "focus manually" would seem just right until you consider the fact that people actually *move*. It's a tough nut to crack, that wide-open aperture one.
I think Eric's answer is what I have been trying to justify to myself. I'm going to try to explain it, and I hope I get it right (I know people will correct me if I'm wrong!).
That is, it is the distance that determines the compression/disortion, not the focal length. However to get the same framing on a crop-sensor vs. a full-frame sensor, you'd need to change the distance if using the same lens on each camera.
In other words, a 57mm focal length on a 1.5x crop sensor, should provide the same perspective and framing as an 85mm focal length on a full-frame sensor if shot from the same distance.
Now, it seems that 85mm-105mm is most recommended for portraits (full-frame), so a 50mm on a crop-sensor might be too wide (you'd have to get in tighter and introduce more distortion). I think this is why you'll see people using a 70mm (like a 70-200mm) for portaits on a crop-sensor (yielding an effective 105mm on full-frame).