This is not a comparison between models, since I think comparing two model of cameras that are in the same line and breed, is not quite logic. This is a digestible summary of the improvements that the recent Canon 5D Mark IV has in relation to its predecessor the Canon 5D Mark III, which happens to have 4 years apart in age, and since technology advances so quickly in terms of processors, electronic components and other innovative areas of digital photography, it makes even less sense to compare the two models. Both are great, and the MKIV has arrived to stay after a very long wait. In between both Marks, there are the Canon 5Ds and the Canon 5Ds R, which made some noise even in the medium format contexts due to their extreme 50 megapixel count.
I will not talk about all the differences between the both, but the ones I think that deserve considering the Canon 5D Mark IV as an investment.
The first obvious one, is that the processor is the fairly new DIGIC 6, in comparison with the previous DIGIC 5 from the Mark III. The native ISO of the Mark IV reaches a little bit higher, up to 32,000. In the previous version, the 61 focal points reduced to a very limited central single point at f/8, and now the camera has the same 61 effective points at f/8. The mirror is motor-driven, instead of the mechanical spring system from the previous Mark III (and almost every DSLR). This is a very innovative step in my personal opinion. The Pixel count has raised from 22.3 to 30.4 megapixels. The autofocus system has also said to be highly improved (even more, could you imagine, wow.) In 2015, DPreview magazine shared an animation that illustrated how motor driven mirror worked, and it is pretty amazing, and can be watched here:
For video makers this is a really important product from Canon, since it allows to record at 4K thanks to the Dual Pixel CMOS AF sensor, and the touch screen may come very handy. The touch screen is really helpful for focusing, since it allows to simply focus on a subject by touching it, not just for video but stills as well. After all, the camera’s prime goal when they engineered it, is to shoot pictures. And even though Canon has their dedicated cinema line; the 5D Mark IV has really opened the possibilities for independent film producers.
Before investing in this camera, you should rent it in order to get a better understanding of all the new features the long 4 year waiting has to offer. If you are currently using a lower level camera from the 5D lineup, the 5D Mark III is still a very wise road to enter the full frame format. And please remember, every camera is just a tool that allows the passionate photographer to capture the meaningful stories that are worthy of preserve in time.