Which fast Prime 30 or 50

I am interested in getting a fast prime lens to use as standard everyday snapshot/walk around. Reason is I want to get some shots with shallow depth of field/Bokeh for more creative effect. I was considering something like the nifty fifty (50mm F1.8) or the 50mm F1.4, but on my 550D these will be equivelant to using approx 85mm lens on my AE1 (film camera from the 70s), this has led me into looking at the Sigma 30 F1.4 or a Canon 35mm F1.4 to get closer to the standard 50mm lens of 35mm film days. How do others feel about this, should I be thinking in terms of film days or look towards the digital age and follow what appears to be more popular and look for a 50mm lens. How much difference is there in DOF with F1.8 and F1.4 lens of same focal length, ie is it worth spending 3x the price of a nifty fifty just to get a bit more apperture. Note I am not looking for best build quality here as I am looking for an occasional use lens and will not suffer the riggors of professional/press style photography. Are there any other options to consider ?

The 50 f/1.8 is a fine lens and will hold up well so don't worry about having to rebuild your house because it exploded when you didn't set it down gently enough on pillows.

It'll really only take out a couple of rooms.

In all seriousness though the nifty-fifty is a great value for the money and I am sure you'll like it.

Which focal length do you like best? buy that one. The DOF with both will be sufficiently thin for most purposes. http://www.dofmaster.c​om/dofjs.html Go here and plug in the same info for the candidates to see the DOF numbers.

One other option to consider is Canon's 28mm f/1.8, which, on crop comes out to slightly more wide than a normal lens. The price is similar to the Sigma 30mm (though it doesn't come with a hood), but it's an EF lens, so if you ever upgrade to full-frame (or if you ever want to use it on an old film EOS camera), it will work. Obviously 1.4 is an improvement over 1.8 in terms of aperture, but each lens has its own set of adherents. I have the 28mm and love it, but then again, I've never used the Sigma, so I can't compare. If you have a camera store near you with both in stock, you should try to test them out on your camera, as each of these lenses is known to have occasional issues with sharpness depending on the copy.

I will stick with the normal range in 135 format and crop equivalent (plus the in between), since that was where your questions seem to be.

If you can get past the pentagon out of focus highlights and a lens that sounds like a windup toy when it focuses (some will add iffy AF especially in low light) then the 50mm f/1.8 MKII is fine. I had one for over 10 years, I traded it because I found a MK1 which is built better. The MKII was still going strong. But if I liked this FL more, I would probably spend the money on a 1.4, mostly for fast AF and full time manual focus of USM (or HSM as I'd probably go Sigma).

I actually prefer my 85mm f/1.8 to the 50mm or my 28mm/f/1.8 when using a non-macro prime. I do shoot an a crop camera. The 85mm is equivalent to the 135mm on my used FTbN and AE1 in the early-mid-80s to early 90s. And you can think of it anyway you want. Just so you use the lens you need to get the image you want.

Look for the the FL you will use the most.

Besides the Canon 28 (there is also a Sigma), Sigma 30 (crop camera only - if that matters to you), and Canon 35L, there is the Canon 35mm f/2. I have not used the 35 f/2 but it seems to be described like a 50mm MKII (buzzy AF and 5 blade aperture) but with better build and most say faster and better AF.

There is also now Canons 40mm f/2.8 pancake. It is not real fast at f/2.8, but is good enough for many. Look at recent threads as it seems to be the flavor of the week because of size, IQ, and the low $200 price tag.

Any of the Canon 50s would work and there are selections for every budget.

When faced with a similar decision for similar reasons, plus the desire to have a lens for indoors that was fast enough to minimize the use of flash, I also looked at the Canon 28 f1.8, 35 f/2, 35 f1.4 and Sigma 30 f1.4.

I eliminated the 50s because indoors, they were a bit tight (85mm equivalent). Then eliminated the two 35s (too slow and too expensive, respectively). That left me with the 28 and the Sigma 30.

The reviews I read indicated that overall, the edge for build quality and IQ went to the Sigma, although there might be a front focusing issue to contend with. However, that would be fixable with 1) micro adjustment or 2) exchange for another copy or 3) sending it to Sigma for calibration.

The Sigma 30 is equivalent to 48mm and, at f/1.4 is fast - both working well indoors. Plus., it's a nice walk around lens. I bought it and have been very happy with it.

Hope this is helpful.