I was out today taking a few shots on the 70D and my new Tamron 28-300 VC. Now I'm fully aware that the superzoom isn't going to be the sharpest lens but I had one a couple of years ago (used on a 550D) and it was pretty good. I was a tad disappointed at the results and it's got me wondering.
Are the 3rd party manufacturers lenses going to be affected by the new sensor system of the 70D by any way. I came home and tried both mine and the wifes lenses focussing by Liveview at x10 mag on both my 70D and my 5D3 where possible. All the Canon lenses (a 35 f2, 40 f2.8 pancake, 50 f1.4, 85 f1.8, 100 f2.8L Macro, 17-40 f4L, 24-105 f4L IS and a 70-200 f2.8L IS MkII both with and without Kenko Pro300 DGX 1.4x and Canon 2x mkIII converters) produced nice crisp images on the screen at full magnification on both bodies.
The other lenses I tried were a Sigma 24-70 f2.8 HSM which produced crisp images with Liveview on both bodies at 10x magnification, however the 120-400 OS and 150-500 OS was crisp and clear on the 5D3 but they weren't as crisp on the 70D (either by AF of MF). I also found the same problem with the Tamron 28-300 VC on the 70D whereas the Tamrom 18-270 VC PZD was crisp on the screen of the 70D.
This was primarily a test to see how good the lens resolution showed up on the LCD of the camera rather than a photo test although I did take shots with all the lenses, albeit I was indoors and so I had to up the ISO to get any decent results. The shots from the 2 long Sigma's and the Tamrom 28-300 weren't great on either body but this was done under normal electric light so I'm not surprized by the results. I've had some good results with the Sigma 150-500 OS on the 70D but the photos still aren't as crisp as they are on the 5D3 and some of the shots I got with the Sigma and my old 60D.
The main idea for the test was to see the IQ of the lenses on the screen and the results have got me thinking that maybe the new 'dual pixel' technology is a step too advanced for some of the older 3rd party lenses. Has anybody else seen this or even tried anything similar. I had to MFA the 150-500 to get the best results out of it with the 70D when I bought the camera but I am surprized by some of the results I saw today.