Now I am using Canon 5D mark II, I want to upgrade my camera into Mark III. I want to know what is the difference between each them.
That is any easy thing to found out :) Just compare the cameras. Here I've done it for you.
As you can see there are several differences. 22 MP vs 21 MP which is really pretty much the same and so is 0.2" difference in LCD size. What is much more significant:
- The 5D Mark III has a 100% coverage viewfinder. With the Mark II you can never see exactly what will be in your images through the viewfinder.
- The ISO range reaches 25600 vs 6400 (or 102400 vs 25600 expanded) which hints that the 5D Mark III is better in low-light and actually it is.
- The Mark III shoots 50% faster, 6 FPS vs 3.9 FPS and for longer.
- The Mark III also has an updated and much faster autofocus system. This fact is not shown in the comparison but you can see that it has 61 AF points to work with which is great for tracking moving subjects.
Here's what I would say are the differences roughly in order of how much they actually matter. If you are predominantly a stills photographer:
Vastly improved AF system (essentially the same as in the 1DX, 60 points, much better performance with f/4 and f/5.6 lenses.
Faster max shooting speed.
Slightly more robust/ergonomic body.
Expanded ISO Range plus slightly better ISO performance in RAW.
Slightly better screen.
New menus/customisation options, in camera HDR
Very slightly higher resolution.
If you are predominantly a videographer:
Lack of aliasing
Ability to output clean HDMI signal with firmware upgrade.
Timecode & AllI compression in camera
The two main deciding factors are:
61-AF points on mark 3
much better ISO performance in mark 3.
You may only want more AF-points for tracking objects, but I believe that even if you do still photography is good to have the option to avoid focus and recompose. I have a Canon 550D, with 9 AF points, like your mark 2, and sometimes it can frustrating, trying to focus and recompose, because of the lack of an AF-point. I know that the central AF-point is always the fastest and the most accurate, but there are times you can't follow this.
High ISO levels are much more in mark 3 and the noise is much less, according what photo examples on the Internet tell.
Hope it helps somehow!