I'm looking for a normal prime lens, desirably fast and not too expensive, for my 450D. 50mm seems to be the normal focal length on FF, thus for APS-C, I need about 30mm.
I want it to be fast as I'm going to use it at night for available light photography. The most interesting candidates so far are:
- Canon 28mm f/1.8
- Sigma 30mm f/1.4
I've read a lot of stuff about both lenses and ended up confused. From my current understanding, the Canon's AF is faster than the Sigma's (the AF should be fast and reliable for street photography - however, I can't tell how big this difference is in practice. Maybe you can help me?) Also, I will be able to keep the Canon when I switch to full-frame. The only thing about the Sigma that keeps teasing me is the f/1.4. How much of a difference is there really between f/1.4 and f/1.8 (what exactly will the difference in shutter speed be)?
Today I got to try out the Canon in a photography store. I'm not experienced with testing and judging lenses though, so my judgement is mostly subjective. The unsharpness in the corners that everybody seems to mention was noticeable, but did not disturb me much (might also be because of the APS-C sensor). What bothered me far more were the purple fringes around bright objects (I tested it at f/1.8). Wikipedia says you can avoid those with a strong UV filter - is that true and does the usage of such a filter have any disadvantages?
Last but not least, if there are any other lenses you'd suggest or factors I missed out, please tell me!
Thanks in advance for your advice :)
PS: I already have the Canon 60mm f/2.8 Macro and am very content with it for portraits. It is, however, way too long for an always-on lens and the 2.8 is clearly too slow for shooting at night.
PPS: Thanks for your answers! Obviously, f/1.4 does indeed make a significant difference. What bothers me the most about the Sigma is that I can't use it on an full-frame camera, which I will definitely buy sooner or later. It is said that you can sell lenses very close to the new price. However, I've read that the Sigma wears out very quickly. Someone else in the same thread replied this was because of the use of suncream. This happens when you read to much. Aargh!
PPPS: I bought the Sigma yesterday. From what I can tell after one and a half day of usage, it works pretty good. The AF needs a little adjustment, but that turned out to be no problem as I currently stay in Singapore where I can just visit the Sigma office personally and wait while they adjust the lens. I'll do that tomorrow and tell you if it made a big difference.
PPPPS: The lens was adjusted a couple of weeks ago so I've had some time to work with it. I have to say, the AF weaknesses are noticeable. However, one has to admit, the focus is required to be much more accurate on a 1.4 aperture. Also, it is an entirely new experience for me to work with such a fast lens so I also had to get used to it.
When I used the lens as an always-on for a few days and then switched to my Canon 60mm/2.8, the focus speed seemed incredibly fast. Hence, my conclusion: The lens can be great, if you know how to work with it.
Answer
A few thoughts and links for your perusal:
- Any reviews you're going to read will be subjective but they can be good data points. Here's a thread on DPreview comparing those two lenses as well as the FredMiranda review page for the Canon.
- You did the right thing by trying out the lens for yourself.
- It seems that the verdict is undecided on whether a UV filter can reduce chromatic aberrations. There is another question on this site about the downsides to using a UV filter.
- The difference between f/1.4 and f/1.8 is 2/3 of a stop. You asked about how this would affect the shutter speed and this means that assuming all other conditions are the same, the faster glass (f/1.4) would allow for a shutter speed that's 66% faster than the slower glass (f/1.8).
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