And the thing is, if you say the 7D has no reach advantage over a 5D2 then you must also agree that usage of TCs is always a waste....
First of all, the money shots there can't be compared meaningfully because they are not the same FOV, and therefore do not target the same output result. For the purpose of advising the OP we are talking about the final output IQ of a 5D2 image that has been cropped to match the FOV of the 7D or t2i. One has to ignore the pixel count and pixel densities, because these numbers by themselves do not meaningfully predict the outcome of such as test.
No, the OP is asking about reach, what he can do when distance limited, nobody cares about your FOV when you are distance limited, FOV is meaningless when you are distance limited.
well, the OP was asking about effective reach with existing lenses on a FF body, in the context of cropping the FF image to yield equivalent final output of the crop body. For this objective, equivalent FOV and IQ of the final equivalent-size output is the measure of success.
He wasn't asking about what lens to use to get a certain landscape shot to give him the same FOV shot from the same spot.
correct; In the paragraph that follows, I point out how different this is from the OP's objecitve.
secondly, I have to admit I'm struggling a bit to see the equivalence of using optical multpliers versus cropping the final image. The comparison is interesting, to be sure, and valuable in its own right, but is not nearly as simplistic as stated. To be sure, optical multiplication introduces side-effects of its own but these are heavily dependant on the TC itself and the native lens to which it is attached. Taking those into account, the advantage is that with careful choices one can present a larger image magnification to the sensor, decreasing the FOV opticallly while taking full advantage of the sensor's native resolution and IQ. This technique will advantage the FF body, and represents a very different test case than the OP has presented. For example, take a photo, properly exposed and framed of course, with the t2i and a 300 f/2.8 lens. Then add the 1.4 III to the lens and mount the combination on the 5D2 body and crop the resultant image to match the 1.6 crop factor of the t2i. is there any doubt as to which will produce a superior result in more situations? To take the experiment further -- mount a 2x III to the 300 f/2.8 and take a photo with the 5d2, then take the TC off and take the same photo with the t2i, croping the result to match the FOV. 5D2 wins.
a single 1.4x TC won't even quite make up for teh 7D reach advantage and here is the point if you can manage to get close enough to the subject with whatever lens and TC you have then you are not reach limited
extending the results that have been posted here, the 1.4x TC on high quality native glass will produce a better image than the 7D using the same lens without the TC, even accounting for the necessary crop of the FF image to obtain the same FOV
when you are limited then he just pops the 1.4x or 2x TC on his 300 2.8 and shoots with his t2i and then does better than his 5D2 with that same combo being shot on his distant bird or moose or t rex or whatever
thats the point in question: will the t2i really do better than the 5D2 with the same optical system attached? The point of results posted earlier is that cropping the 5D2 image to produce the same final output size produces IQ that is remarkably similar to the 7D, with perhaps only a small (if any) advantage to the 7D. That result may be debateable, but is the basis of my point.
if he has a 1.4x and not using it, then he is not distance limited. You are only distance limited when the same optical system is used on both cameras. The point of results posted earlier is that when truly distance limited, the FF image can be cropped to the same FOV of the 7D and produce results that are better than the numbers imply.
Therefore, if you are not distance limited for the 7D, and you have a 1.4x in your pocket, then adding the 1.4x to the 5D2 should produce even better results than the 7D because the 5D image requires only a small amount of crop in post to acheive the same FOV.