A month or so back I posted a very similar thread, looking into the sharpness of various lenses in our camera bag, and decided to do the test a second time, this time taking a bit more care with camera settings
ALL cameras were hit with a 'factory-reset' before the test to return them to factory defaults ... thus erasing any issues with anti-noise, or extra colour saturation etc etc
I've had fun doing these side-by-side comparisons with our houseshold's variances of cameras & lenses.
> a Panasonic FZ100 with 24x zoom [rated by panny as equivalent to 28 - 672mm in film camera terms]
> a Panasonic G2 with the panny 45-200 lens [equiv to 90-400mm] and its 100-300 [eq 200-600], and
> a Pentax Kx with Sigma 28-300 [equiv to 42-450mm] and a 70-300APO [105-450mm]
The 'target' house is across the street - about 125metres [400feet] away;
all cameras were set to 12mpx - ISO-200 - WB-sunny - Exposure as "A" aperture-mode, autofocus & metering were set as 'centre-weighted'. Even with a factory-reset to defaults, there were minor colour differences are visible
Even though each camera was set to 12mpx, slight pixel variations occur between camera makers, so all images were normalised to 4000pixels wide. Then, to create the side-by-side images, each camera image was "sliced" into a 900w x 1800h crop, and pasted onto a 3600px wide canvas [thus covering 4 slices]
Vertical differences via tripod movement were attended to via pushing the image up or down [and creating a broken top & bottom edge], and the final aligned images were cropped and tidied up to 1500 pixels, with a 300 pixel white lower border then added for text [and returning them to 1800 pixels high]. Images were then downsized for posting to 1200px wide and saved to keep the image-size at 250kb for posting here
1- here is the target house
2- centre image comparisons
3- edge/corner image comparisons
The FZ is beautiful & easy to use, the G2 is delightful in its size & weight, the Pentax is up for sale as [like all APS-dSLRs for us] even though it's a small dSLR, it's too large & heavy for our comfort levels
The Sigma 28-300 is obviously a poor example from its maker, as others here have commented from the earlier post. This lens was bought 2nd-hand some time ago, and I guess its original owner did similar tests and was happy to dispose of it. I am now doing the same, but can't even give it away!!