The Canon 50mm F1.8 is a little gem of a lens for it's price, and because of that it's one that I recommend to all beginners over the kit lens. However, there is another 50mm made by Canon which is not too mind-crushingly expensive - the Canon 50mm F1.4 version.
I know many people with the F1.8 will have considered upgrading to the F1.4 (or wondering whether just to buy that one straight off and bypass the F1.8 version), and wondered whether it was worth the price. Well, I upgraded a couple of years ago, but before I sent my old lens off to it's new home, I did some comparison shots to see how much difference there was between the two.
I took some tests shots of the same subjects, in the same light, with exactly the same settings and have done nothing to either of them in editing. This wasn't done in exactly the most scientific method and I'm no expert on lenses - so this is definitely a "real world" view and not a test lab comparison! (But really, we don't take photos in test labs so if you have to pixel peep the difference isn't worth it in my opinion - for what that's worth!)
With that caveat in mind, here's my thoughts on the 50mm F1.4 vs F1.8......
Without a doubt the F1.4 is sharper - it's not by a huge amount, but there is definitely a noticeable difference at lower apertures - although not wide open. Stopped all the way down, both the F1.4 and the F1.8 are quite soft - it's only when we get to about F2.0 that the F1.4 starts to take the lead in sharpness. By F4.0, they are quite close again. In the photo below (which is the same picture as the next one but just cropped to show just the watch face) the shots were taken at F2.0 and there is a very notable difference in sharpness.
My reason for upgrading from the 1.8 was because I found the auto focus to be a bit slow. In this regard, the 1.4 is quicker, especially in low light - it doesn't hunt for so long as the 1.8 does, and it latches on much quicker. The other difference is the noise - the 1.8 clunks about getting focus whilst the F1.4 version is much smoother and less noisy. The F1.4 has a USM motor and you can just hear and feel the difference - I can't think of a way to quantify this on a written blog so you'll just have to take my word for it!
I would say the bokeh with the F1.4 is slightly better than the F1.8. It's a little bit softer and smoother - not a huge difference but a slight improvement. This is due to the fact that the 1.4 has an 8 bladed aperture, and the 1.8 only has 5. (I forgot to take a photo of light bokeh, if I had you would see that the light circles would look more like a pentagon, with 5 definite sides. With the eight blades, it looks a lot more circular and smoother)
Color / Contrast
I took a few different comparison shots of the same subject but I really can't see any noticeable difference between the two in terms of color or contrast- both look good to me. These were both taken at F2.5.and you can see in these shots too that the F1.4 is a little bit sharper - it's not so noticeable sized for web but you can see it more clearly when zoomed in that the F1.4 has captured more detail.
Weight / Build Quality
The 50mm F1.8 is incredibly lightweight, and feels more like a toy (it's called the plastic fantastic for a reason!) One hard knock on the ground and I doubt the F1.8 would hold up. Everything is plastic, including the mounts. The build quality is a major difference between the two - you'll notice it as soon as you pick up the 50mm F1.4. It's slightly heavier, and feels and looks a lot more robust, and it has metal contacts (it's still not as robust as my other lenses though I have to say!). It also has a distance scale which the 1.8 does not, this can be useful when working out depth of field (not that I ever use this, but if you did!)
To sum up, the 50mm F1.8 is a brilliant little lens for the price, and it will work wonders for you. It's very sharp, but not so much wide open or at lower apertures - try using it F2.8 or above (it will change a little from lens to lens) It can also be a little bit of a pain to focus, especially in low light, so try to shoot in areas with more light. (Read these tips for shooting with the Canon 50mm F1.8 to get the best out of it) I believe it is in these two areas where you will mainly see a difference if you upgraded. Overall, the F1.4 is sharper, quicker to focus, slightly better bokeh and has a slightly better build quality. On balance, I would say that the difference in image/build quality probably equals the difference in price.
So is it worth the upgrade? For me, the answer is yes. It's was probably my most used lens (until the Sigma 35mm entered the frame, more on that later) due to the fact that I love the focal length, and I like that the fact that it focuses quicker than the F1.8 did - especially in low light. (This is handy with children who do move about a fair bit!) Also, because I generally shoot with apertures around F2.0 to F3.2 mark, the lens is definitely sharper at those apertures, which I appreciate. Of course, if you shoot outdoors with plenty of light, and you generally shoot at around F4.0 or higher, and your subjects are stationary, then I am not sure that the upgrade would be worth it for you.
There is still plenty you can do to help your 50mm F1.8 do a great job though. The slightly slower focus is one concern, so you really want to get your focusing skills down to up your hit rate of keepers.
Either way. both lenses are great - if your budget only stretches to the F1.8, then it will do you proud. Otherwise, the F1.4 is serious option if you have more cash to spend, and would like a little bit of extra quality.
You can see more information on both lenses by clicking on the links below: