amfoto1 wrote in post #16138013
Both images are underexposed by about a stop, but yes there is some difference between them. The one you identified as coming from his lens isn't as sharp as the one you identified as coming from your lens.
Try swapping the filters from one lens to the other and see if it makes any difference.
Be sure to MFA the lenses accurately. And lock them down on a tripod. Use mirror lockup or Live View. Either use a 2 second delay or use a remote release so you aren't touching the camera at the moment of exposure. Turn off or be sure any in-camera sharpening is set the same. Best to use the same body for both lenses, which it sounds as if you are already doing (a dirty sensor can effect resolution, for example).
In other words, try to elminate everything possible aside from the optics themselves, in your testing. There are a ton of things that can throw of sharpness!
If there's still lots of difference, send the weaker lens back (if it's new and the retailer will exchange it) or send it to Canon for a tune-up.
There are many things that can happen to a lens... ranging from some problem missed by quality control to a dropped box during shipping to the buyer... Why fret over it? Send it back and get it fixed.
Changing the filters was not something we tried. That being said, as I was so curious about this, I just drove up to his house and tried running the same tests with:
* My filter in both lenses
* His filter in both lenses
* No filter in both lenses (just for the heck of it)
We also used live view with remote control and mirror lockup (as we did last time). The results are the same, identical. His filter was worse than mine, but anyways, it made no difference.
At F2.0, the center of the image is pretty similar, in fact I could say identical. At F2.8 mine looks a tad better. At F4.0 and above using the extender, there is big difference.
The corners is a whole other story, even at F2.0, there is big difference and it gets worse as you add the extender. All corners exhibit this issue, I cannot say if it's equal or not, but all of his corners are somewhat softer than mine.
Interesting how there is such variation between lenses. The sad thing is, 95% of the people buying an L lens won't have the opportunity to compare it with another one side by side like we did and doing this with the extremely expensive telephoto primes is even less likely. Paying all that money for a lens, you expect to get the best, seeing this much variation was not something I expected.