I'm looking for a general purpose camera that can do almost any type of photography.
The 5D Mark II is great for portraits and ultra-wide photography, but for wildlife photography, which is better, a 7D (with crop sensor) or a 5D Mark II with teleconverter?
From my experience with my 7D and now a 5D (mkIII), I'd say for wildlife stuff, the 7D would be your preferred choice, for four reasons:-
APS-C 1.6x crop sensor. This will extend the reach of any and all lenses you put on your camera. A 200mm becomes a 320, a 400mm becomes a 640, etc.
Using teleconverters will cost you light, and therefore require slower shutter speeds to effect the correct exposure. A 1.4x tele will reduce light reaching your sensor by 1 stop. A 2x tele will reduce light by 2 stops.
For wildlife, especially birds in flight, you need a rapid fire shutter. The 5D Mk II will offer you 3.9 frames per second, whereas the 7D will offer you 8 fps.
Auto focus system - the 7D's 19 point advanced AF works really well (and I'm talking from experience) at locking on to and tracking fast, eratically moving subjects. I don't think you'd get quite the same from the 9-point diamond of the 5D mk II. (Caveat, READ THE MANUAL - will require good knowledge of how it works, and customisation from the Custon Fn settings within the menus to get the best from it and for it to work how you need it to).
Points 3 and 4 are mitigated somewhat with the 5D mark III. The fps is upped to 6fps (still not quite as good as the 8 of the 7D), and the AF system is upgraded to the advanced 61-point AF from the 1D-X. I have yet to give this a good workout yet though.
There may be stuff I've forgotted but from my experience, those are the things that jump out at me. Hope that helps :-)
The 7D and the 5D mk2 are simply different cameras designed with different types of photography in mind. The 7D is designed for capturing fast action, while the 5D mk2 is designed for slow or still subjects. The 7D is ideal for sports/wildlife while the 5D mk 2 will be hard to beat for landscapes, portraiture etc. The full frame 5D mk2 offers 21mp (5616x3744), while the 7D offers (5184x3456). The 7D's x1.6 crop factor can help with reach, but the high number of megapixels crammed into the smaller sensor makes it more suseptible to noise in low light (especially at higher ISO's), but this can be dealt with in PP. The autofocus on the 7D is definitely better & in AI Servo fast subjects can easily be locked onto. The 7D also has a shorter shutter lag & reacts faster when you release the shutter. Another point is that there are more lenses available for the 7D as it takes ef-s and ef mounts. As for using teleconverters, all teleconverters degrade image quality to some degree as well as losing light, so while the 5D mk2 offers better image quality, using teleconverters with it will reduce this quality advantage.
It all depends on the light!
I'll explain. I've got a 7D and what you gain in crop factor magnification (thus saving you a lot of money on lenses) you lose in image quality. On the 7D it's very, very hard to get tack sharp images because your starting point is pretty much like you're always using a digital zoom at 1.6x magnification on a full frame camera. This difference in image quality caused by the lack of sensor size and quality (compared to a 5D MkII and a 5D MkIII) is immense in the real world. The guy I sit beside at work brought in his new 5DMkIII and image quality is simply in a different league.
Now, I mentioned light. I live in the UK where intense sunlight is not the most common type of weather that we see. This means that fast glass is hugely important, the weather also means that our wildlife sits in lush green fields or leaf laden trees and thus getting decent shots with sharp contrast is also really hard work. So, when you consider that the 7D autofocus uses colour information as well as contrast in its processing then I am certainly figuring out why I'm finding it hard to get crisp shots.
The low intensity of light in the uk means I have to use prime lenses (oh what a shame i hear you cry) but this means that i've got very little depth of field to play with and thus I get the beak of a Kestrel in focus but the tail is in a world of Bokeh. This obviously means I have to stop up the aperture but without the light intensity I'm forced to up the ISO to maintain shutter speed. It is in doing this that the difference really starts to show. The sensor of the 5D's are so much better that the raising of the ISO has almost no effect on image quality.
Comparing my 7D with both of the 5D's in good (but not intense) and low (cloudy dull or forest) light shows a difference on a scale of amateur vs pro. It really is that stark.
Now, in the UK or in so-so light and better, the 7D is a very, very good camera, especially with prime glass and especially with subjects that are 5 to 200 yards away. In intense, overhead sun, USA or continental European light the 7D is a truly professional level piece of kit (most of the movie "127 Hours" was filmed on a 7D) and you'll wonder why people pay 3 times more to own a 5D, but I'll say this; - if it's a bit cloudy, and you're trying to shoot a Kingfisher 150 yards away then whilst you are boasting about a better zoom level than the next guy on a 5D with the same lens, when you crop the shot to the same size you'll see that his shots are curiously crisper than yours because; firstly, his sensor is simply a better quality piece of silicon than yours, secondly, his sensor is better than yours and thus his camera didn't spend a whole lot of processing time whilst using colour to drive the auto-focus, and thirdly, his sensor is better than yours and thus his shots taken at ISO 2000 are usable keepers whilst yours taken at the same ISO (and less) look like a badly tuned tv screen.
A 7D might save you cash by 'giving the effect' of a 1.6x longer lens but what's the point of getting a crop-factor induced zoom that gives you 9fps of closer, noisier, 'blurrier' pictures? As I said, in bright, sunny conditions the 7D fires on all cylinders and gets to within 90% capability of the 5D but when you're doing long lens stuff in average light I'd go for a 5D MkII as you'll never really use the video.
