After reading Dan post (a while ago) about wide angle lenses with wide aperture, it got me thinking. While I have been happy with my 17-40L4, as it is wide enough for pretty much everything I do, going wider would open the door for more creative shots. Ex: having an even better separation of foreground and background objects. Also, Dan reviewed lenses from a 1DMrkIV perspective so I wanted to see what was out there for full frame owners.
Before going into the list of available options, I think it is worth looking at the effect of wide aperture on wide lenses. After all, the goal of this exercise is to find a wide angle lens that will give us some control over DoF. As we all know, a wide aperture allows more light into the camera which allow us to shoot in lower light which is always good. The other result of aperture is too control the depth of field (DoF), which is another familiar concept. The thing you might not be aware of is how hard it is to get a shallow DoF when shooting ultra wide.
For most of us, this is a good thing because it allows us to shoot in low light without having to worry about keeping the subject in focus. But what happen when you need to shoot wide and want a shallow DoF? Lets look at some numbers.
Suppose a subject that is 1m away from the camera and see how much DoF (in cm) we can get with the following aperture 1.4, 1.8, 2, 2.8, 4 and focal length 10, 12, 14, 17, 20 and 24. One meter may seem close but when you are shooting below 24mm, it almost looks like a medium framing.
As you can see, the DoF gets bigger pretty quickly as you increase your field of view (use small mm lenses). If you increased the subject to camera distance, the DoF increases even more (not shown in the chart). The rules of optics haven’t changed for wide lenses, it is just that most people don’t realize how the formula reacts when applied to short focals.
So, how do you get a shallow DoF with a wide angle? Same rules as when shooting a portrait: get the subject close to the camera, the background as far as possible and use a large aperture!
Now that we have a better idea of lens requirements for such a job, lets see what is available.
16-35mm f/2.8L II USM
The the standard wide angle zoom of many pros. While the first version had some technical issues, this one is pretty close to perfection and insanely sharp. My only complain would be its price. At over double the price of the 17-40L (see next), you have to wonder if the added stop of light is worth it. This is especially true for video where you dont need all the resolving power this lens has to offer compared to cheaper alternatives. It is also good to know that it uses a 82mm filter so you might have some issues with your ND or circular polarizer. This lens is quite useful once mounted on a Steadicam since its wide aperture allow it to have enough DoF to shoot in low light while maintaining a reasonable depth of field to keep the subject in focus.
This is my favorite lens because it can zoom to a natural perspective (35-40mm) or truly exaggerated perspective at the wider end . All the things we said about the 16-35L holds true for this lens except its filter size of 77mm and lower cost.
This is the widest Canon lens you can get. Ridiculously sharp, its usage is limited but always spectacular. The lens is not a fish eye, in fact straight lines remain quite straight which make it a favorite among landscape photographers.
While 24mm should not be considered super wide angle, this lens deserves mention as it is in a class of its own. It is the widest aperture wide angle you can get (from any brand), which make it the best choice for low light shooting, while performing incredibly well for both stills and video. Of all the lenses we are listing above, it is the only one truly able to shoot wide and have a shallow DoF.
This is the widest Canon mount zoom lens you can get. While the aperture is too small for shallow depth of field (you hit the hyperfocal very quickly at 12mm) or low light shooting, it is an excellent lens for everything else.
I already talked about this lens on the best third party lenses article. It is wide and ridiculously fast. Looking at the chart above, we can see that it the only lens with the Canon 24L to be able to really get a shallow depth of field and achieve subject isolation. And want to know the best part? It is almost four time cheaper than the Canon lens! I would never rule this lens over the 24L for stills but, for video, it is sharp enough to get the job done. Of course the lens has some technical issues, like not being super sharp when wide open, but that is not such a problem when doing video since you are working at a much lower resolution.
If there ever was a reason to switch to Nikon, this lens would be it. It is nothing short of extraordinary. Of course, it is priced to match its performance. Still, in my opinion, it is worth it! I have never used this lens on my 5D (only on a D3) but since there are no aperture control directly on the lens, I suppose the aperture will stay at f2.8 if you plug it on a 5D with an adapter which is what we want anyways.
If you are looking for a low light/wide aperture wide angle, there isn’t much choice: go with the Sigma 20mm f/1.8 EX DG it will get the job done. If it is not wide enough for you, you will have to look at the zoom alternatives we have outlined above but understand that none of these will allow subject isolation like the Sigma does.