Desertraptor wrote in post #14061274
Not another who believes in fairies? Or you trolling me?
Putting a EF lens on a crop body does not magically increase your focal length. It's an illusion fed by morons at the local camera stores on the unknowing and the fact that a crop camera actually crops the image for you which gives the illusion of increased magnification. A 50mm EF lens is and always will be a 50mm EF lens no matter what body it's on
You're right... and you're wrong.
A 50mm is still a 50mm.
But actually an 18MP APS-C camera "puts more pixels on target" than a 21MP FF camera does... so there is some "free teleconverter" effect. It's just not all of the 1.6X "lens conversion factor".
The pixel site density of the 7D is more than twice that of the 5DII. The crop camera has approx. 53,923 pixel sites per square mm. The FF camera has approx. 24,336 pixel sites per square mm.
Thats's a factor of 2.22X more pixels per square mm in the 7D. Yet the lens conversion factor is only 1.6X.
Now this doesn't take into account other factors such as the quality of those pixel sites, differences in lens resolving capabilities, and the anti-alias filters differences between the two cameras, so it's rather simplistic... But yes, the 7D offers some "free teleconverter" effect. It's somewhat less than 1.6X, but still is more than 1.0X.
I use both and will usually choose the 7D for most subjects that call for some telephoto reach. In order to achieve similar subject framing that I get with a handheld 300mm f4 lens on the 7D, with the 5DII I'd need to use a much larger, heavier, and far more expensive tripod/monopod-only 500/4 lens.
There are plenty of other reasons I'd choose to use the 7D over the 5DII in various situations... Or, vice versa, times that I'd choose the FF camera instead of the crop. That's why I have both.
If I think I'm going to be using the images very large, I'd rather shoot with the FF. I also prefer it for greater control over depth of field and the way it renders bokeh with large aperture shots. It would typically be my choice for landscape shots, portraits, and often for macro... all situations where the FF camera's characteristics can be beneficial and it's shortcomings are minimized.
But the 1.6X camera is closer to FF in image quality than many people give it credit for... There's an awful lot of "full frame goodness" hype flying around. I'll use the croppers when I need better AF performance, higher frame rates, "more reach" and/or want to keep my lens kit as light as possible. Also, the 5DII's shutter is louder and more likely to draw attention in some situations (glad to see the Mark III has a quiet mode... Canon should be able to make the camera a lot quieter... after all, they made the Elan 7/EOS 30 models, which were very quiet "FF" 35mm film cameras.)
Plus, a crop camera allows you to use a smaller, lighter lens kit... And gives you full access to an expanded line of lenses. I.e., in the Canon system a cropper can use both EF and EF-S lenses. But FF is limited to only the EF lens choices.
On the other hand, the 5DII has about a one stop higher ISO advantage over the 7D (that's my estimate and opinion, some folks feel it's more)... And the FF camera's AF system will still work, albeit slowly, about 1 EV lower light than the 7D's. So, IMO, the 5DII is the better choice for more challenging low light shooting.
Dailydriver, a 50mm is always a 50mm. But that 50mm behaves differently on different image formats. When you change image format, any given focal length's Angle of View changes. That 50mm behaves as a "standard" lens on what we now call FF (24x36mm format). The same focal length on a "crop" camera that uses a smaller portion of the image circle projected by the lens behaves as if it's a short telephoto lens.
If Canon also made medium format cameras that could be fitted with the same lenses... say a 6x7 (image area 60x70mm approx.)... that same 50mm lens would be a super wide angle instead. Of course, this is merely theoretical because the lens would need to be significantly redesigned to offer up a large enough image circle to cover a 6x7cm image.
The corollary of the focal length discussion is that while that 50mm behaves as a short telephoto on that crop camera, approx. a 30mm becomes a "standard" lens on that camera (but would be a moderate wide angle on FF).
The only time you really need to worry about lens conversion factors is when switching between image formats. Someone who only uses the more common, so-called "crop" cameras that have the approx 15x22mm sensors, really only needs to worry about how lens focal lengths behave or perform on their particular camera. On the other hand, someone who uses a combination of formats or is making a change between image formats has to give the lens conversion factors some thought.
This isn't anything new and unique to digital cameras either... We had to do the same thing with film cameras in different formats. A "standard" lens for a 4x5" view camera is 180mm, for a 6x7cm medium format it's 90mm, for 645 (4.5x6cm) medium format it's 75mm, for 35mm film it's 50mm. And for so-called "half frame" cameras that make 18x24mm images on the same 35mm film, a standard lens is around 32mm.
As to the OP's original question, the 5DII's AF system isn't nearly as capable as the 7D's tracking moving subjects. Of course a 5DII can be used for sports and other action, but it will be more limiting (center AF point only), struggle more than 7D to maintain focus on subjects in AI Servo mode, and your "keeper rate" will be lower due to more missed focus shots. But you didn't mention what else you shoot or why you think FF might be a better choice for you... Only that you "shoot Formula 1 about twice a year". So I really can't say if 5DII would be a better choice for you. By the way, if you do make the switch, I bet you could rent a camera for those rare occasions where you need to shoot sports/action.
But there are other factors to consider, besides just AF performance. For many things the 5DII might be more desirable. Or it might not. If you never print any larger than, say, 13x19 and/or most of your use of your images is online at Internet resolutions, then the 5DII would more likely than not be wasted. On the other hand, if a lot of your shooting demands max image quality regardless, such as wedding work where there's a whole lot of intense competition for the business, then the FF camera might be best.