Instruction: Answer the given question by extracting information from the supporting document.

Input:
Question: Will this work on a canon 5d mkIII?
Document: It's entirely up to you. Me, I served aboard a frigate(DLG) but prefer my kayaks and I sure would like a 5d mkIII but it'll have to wait. Ah, frivolity.
bought this to fine tune my lens. it worked and damn was i mad. my telephoto lens is not sharp unless I'm using flash or a strobe unit...weird. my 35mm f1.8 is so backed focus i  couldn't even fix it in camera. and my kit lens happens to be the sharpest. The product  worked so well that I'm switching over to canon now haha
It won't help with missed focus  issues, though (e.g., when focus falls on a nearby tree rather than a person because of a weak focus mechanism (lack of cross type sensors) as with the Canon 5D Mark 1 and Mark II)  - those are inherent to the camera itself.Lenses can get knocked, bumped, or simply fall out of consistent focusing and start back focusing or front focusing away from your intended focus area.
I own a Canon 5D Mark II camera and 5 Canon lenses. I haven't noticed any issues with my lenses, but thought it would be nice to know that for a fact. This is a very simple method to calibrate lenses. It is basically a ruler propped at a 45 degree angle. You can use a one foot wooden or plastic ruler just as well. But this is an all-in-one structure to make things easier. I put my camera on my granite countertop which is quite level.
I purchased it to calibrate my Canon EF 50mm F/1.2L since some of my images just seemed softer than I was expecting.It's made of a sturdy plastic that folds down flat for easy storage. The focusing surfaces of the device are covered in matte finish plastic stickers. On my copy, the vertical plane sticker was slightly askew, but I didn't feel that it would affect focusing accuracy.Overall, a great tool, but I deducted one star for price.
Stacks of objects arranged so that each is just a little further from the camera than the next (AA batteries standing on end). That was a lot of work also, and not easy to judge very fine distances.3. Shooting an object (like a book page with lots of text) at a diagonal angle... hard to make sure the camera is actually focusing right where you want it to, so the results aren't totally trustworthy...Anyway, there are other options.
On the camera LCD you can vaguely check your work. Because the target image will be fairly small, you'll have to blow up the playback to maximum size. At this point, basically check to see if you can read the numbers and lines clearly (you didn't get camera shake and the exposure was somewhere near right). If all looks good, repeat the image two or three more times (each time rack the lens to infinity focus).
I knew my lenses were not focusing correctly and I tried the manual approach of printing out focus test charts from the web and trying to do the 45degree angle thing with a tripod, it didn't work as well. This takes all the hassle of the manual process and makes the calibration easier to accomplish.I'd agree with a lot of the reviewers that this is an overpriced piece of kit for the what you get but I think in the long run it will pay for itself.
If the SpyderLensCal design wasn't so flawed, I would not mind so much paying $65 for a piece of plastic if the system actually worked. I returned my SpyderLensCal after I realized that the process wasn't perfectly repeatable. The problem is a design issue - there is no way to insure that the camera is perfectly perpendicular to the focus target, so accurate calibration is not possible. A simple sighting tube through the target focus point would work perfectly.
I set up the 'Datacolor DC SLC100 SpyderlensCal Lens Cal. Sys. ', which took no time at all. And, frankly, I don't know what the fuss is all about because this device works, and If you're familiar with your camera then it couldn't be easier.I've a 5d mkII with 4 lenses and as soon as I received this Lens Cal. system in the mail this A.M. I had it set up and all lenses verified as accurate. What can I say.
Answer: Yes, it will.