Canon’s little pancake, the EF 40mm f/2.8 STM ($199, click here), is getting a lot of attention. That’s no surprise, given the outstanding performance this lens delivers (especially in regard to its price). DPreview published sample pics shot using the EF 40mm f/2.8 STM (click here). The sample pics were shot using an EOS 5D Mark III and an EOS 5D Mark II for full-frame images, and using a Rebel T4i/650D and a Rebel T3i/600D for the APS-C images.
Our friend Carl over at photographic-central posted an exhaustive review of the pancake. Carl used a full-frame (an EOS 5D) and an APS-C camera (an EOS 50D) for his tests. His review confirms the exceptionally good performance of this pancake lens. From the conclusion:
Overall the Canon EF 40mm STM f/2.8 lens is a lot of bang for the buck. Certainly better results can be had with lenses at different focal lengths in the max magnification (macro) and bokeh categories but the 40mm STM does quite well considering its price anyway, especially so on the APS-C format. Sharpness is never an issue at f/4 and beyond on both formats, and sharpness only gets better up to f/8 corner to corner where it seems to reach its peak when all things are considered (center is barely softer at f/8 vs f/5.6). Barrel distortion at least in field conditions, is slightly noticeable but not really a problem.
Vignetting shows up even on APS-C but nearly gone at f4. Any weaknesses this lens exhibits (very few) are more pronounced on a full frame sensor but this lens still performs well over all considering its low price. Color and contrast are just phenomenal at f/4 and beyond on both formats, a highly desirable trait indeed. Flare can show up in extreme circumstances so I recommend a hand/hat/hood to combat it if its a problem for you.