I have now owned the Canon 40mm STM lens for a few months and have been able to use it in various circumstances on various camera bodies. It’s a nice lens, but maybe not for everybody. Let’s first look at the let downs: Build quality, no complaints. It’s light, it’s solid, and it inspires confidence, but It’s really small!
I liked the idea of the pancake lens, and I liked the idea of having a very small camera “package” when moving around, but when you use it on a big camera like a 5DmkIII, know that you will be shooting like a tourist! There is no place to hold and stabilize the lens/body combo!
It’s also a lens that doesn’t really want to focus manually. The focus ring is very narrow and fidgety. If you are shooting at minimal focussing distances with shallow DOF, you end up more often than not missing the actual focus point. I would turn the focus ring, and turn and turn and turn (did I mention it has a massive focus throw?) and then when you get to the point where you want focus to be and let the ring go, it is like it falls just before or just past the point you wanted to focus on. Not the end of the world, but not fun. It’s most probably due to the focus-by-wire function (manual focus is electronically controlled, not manually moving the lens assembly as other lenses in this price range).
Now, that long focus throw is almost the worst of both worlds. If you are shooting video (touted feature of the lens and new STM motors when used on the smaller bodies with active AF during video) with the lens on and have to focus manually, like on a Canon 5DmkIII or 60D, the throw is too long to do a smooth focus pull. You often end up bumping the body as you can’t do a smooth pull in a single hand motion over any significant distance.
And that is about as nasty as I can be about the lens. The rest is pure honey!
When you use it in AF mode the response is quick (not as quick as my L lenses, but pretty snappy) and it locks focus without hesitation. The image quality is good straight through the average use aperture range. Focussing is slower on the EOS M when used with the adapter, and also slows down appreciably on the DSLRs when using live view, as does all lenses, to be fair. Canon has started updating camera AF during Live View with firmware and its done wonders for the Canon EOS M so maybe this will not be such a big factor in the future.
f/2.8 will give you very good results in the middle 50-60% of the image and more than acceptable coming to the edges of the frame. Pick f/8 and you have a super sharp lens pretty deep into the corners with a fairly pleasing bokeh.
The lens also features FTM – Full Time Manual focus, so you can adjust focus without switching to MF-mode right after initial focus lock is completed. This is a feature I have found handy on my other lenses at times, but maybe a bit difficult to use when on a big DSLR body.
On an APS-c body, the vignetting at f/2.8 is marginal at best but more prominent when using a full frame body. Nothing your RAW converter and the new camera bodies (if shooting JPEG) won’t correct at the drop of a hat. To give you an idea of how little influence it has, I never realized there is was any kind of vignette until I started comparing Out-of-Camera jpegs with the neutral RAWs. The falloff is very gradual and I think that is why it’s not intrusive in most shooting situations. Off course the vignette reduces as you stop down as well, so I don’t see it as a major negative for a lens of this price.
Also important to note: Flare
This lens is very short and doesn’t come with a lens hood. I shoot absolutely everything with a lens hood to reduce light bouncing onto the front lens element as much as possible, but I was quite impressed with how well this lens handled contrast even with the sun in frame. I would think that the construction of the lens would make manual focussing very difficult if you did attach a lens hood, though, but as is, I doubt whether I would buy the lens hood at this point in time. Will see how much I use the lens in the end and if a lens hood will be justified.
On the lens you will notice it says “Macro” I don’t know why. This is no macro lens, by no stretch of the imagination! That said, this lens responds ridiculously well to extension tubes! I thought, as a 40mm lens I can pop a 36mm extension tube on it and bring that distance down. No go. Waay to much! ended up with the 12mm extension tube giving me very close to 1:1 macro (very unscientific, complete thumbsuck estimate. The only unfortunate is that with an extension tube, the minimum focus distance is down to 18cm with max focus distance at about 20cm, nothing longer, nothing shorter, so it’s a bit limiting in your framing – will just have to work around that, I guess.
I have been looking for a long time at the 50mm options to replace my current 50mm f/2.5 and have not been able to find a perfect replacement. I didn’t want the 50mm f/1.8 because I do believe I will work the lens to death in a short time. The f/1.4 was just too soft for the money, (not to mention the f/1.2!) so far, I think this just might be it. I was initially worried that the 40mm would show more FoV and focal length distortion but right now it’s has less distortion than any 50mm fixed focal length lens Canon produces. Big bonus!
Conclusion? I think this one will become part of my full time kit.