This has been an interesting thread. The main reasons for going to a good FF body it seems are- better high ISO/low noise performance, better for wide angle to normal and short telephoto with lower distortion and able to design this FOV with a faster lens, more DOF control, and to use good legacy glass in their original FOV. The latter is my own main interest. The Tokina AF 20-35mm f/3.5-4.5 came in three models. The earliest was one having a 72mm filter size and was highly rated for sharpness, but had some serious vignetting at wider apertures. Then came the 2nd one which has a 77mm filter size, and tested out to be actually 19mm, still with metal-body construction and a fine lens overall. Last came the 19-35mm in a plastic body construction, but of good quality, and was less expensive. It was probably the same optics as the previous model.
@Igor123- If your very fine DA 12-24mm f/4 was delivering the goods (I also have one and agree) what was your reason for going to the K-1? For landscape use, is deeper DOF control that important? Why not go for a KP which has near the same advantages of high ISO/low noise and advanced resolution, better AF, etc and save yourself some weight-carrying?
Now that you have your K-1, I address your question. While test charts, DxO, lens-teeing machines, etc can be a useful guide to a point, I am always very interested to see how a lens performs when taking an actual image compared to another highly-rated lens. As to corner softness, let us not forget we are talking about corners, of which there are only four to a frame. A very small percentage of the photo. In reality, how much important information do we find in a corner, and how often? Edges are obviously much more important, though they are not always important.
So let us take a look at test shots of the same subjects. I think we should disregard the Canon 24-70 f/2.8 because Canon chose not to include image stabilization, as one reviewer commented, to achieve the greatest-possible sharpness. Well, what? I'm sorry, but SR can be an advantage at slower shutter speeds, even at 24-70mm, so there goes any sharpness advantage on a test bench, unless for tripod use only- then there goes the versatility of a 24-70mm walk around lens.
Google the Tamron 24-70mm f/2.8 lens. When they come up, disregard the G2 version, and look for the test on Imaging Resource of the Di VC USD SP version, which is the counterpart of the Pentax DFA lens. There are more tests of the Tamron than the Pentax. When you get this test up, scroll down to the still life test shot. On the way down, you will notice several alternative lenses which have been tested in the same shot. We will come back later to compare the VR version of the Nikon, which was done using the same camera as used with the Tamron. Now go on down to the test shot for the Tamron and click on it. Up will come two tests of that shot with this lens, one APS-C, which be sure to disregard and use the FF one with the Nikon D800e camera- click on 24mm f/2.8. You will now get a high-res image. Forget corners, let's look at edges. To your right will be a cup with 2 bruhes and a numbers chart. Put your pointer between the far right brush and the numbers chart and click. Now you will have a super blowup very near an edge. You can judge for yourself how much sharpness or lack in this extreme blowup. Click again to go back- now put you pointer on the lettering at the bottom of the Samuel Smith label, also near an edge. Look at this, then go down to the charts lying below. You will see some added softness creep in but only right at the very, very edge!
Click aging to go back then close the page. Then close the page showing the 2 images with the APS-C shot. Now you are back to the main teat page, and go up to the Nikon VR lens, click on it and to scroll down to do the same examination, being sure it is the FF one. While you are there, also check out the 70mm shot. Unfortunately, the two lenses are tested differently at middle FLs- 35mm for Nikon and 50mm for Tamron. When you are finished and are back to the Nikon lens main test page, use your back button to get back to the Tamron main test page and check out the FF 70mm test in the same spots of the image. I think you will find the Nikon to be better at the longer FLs. but not so at 28mm and probably not so at 35mm. So in the mainly shorter FL range of your concern, what is your impression in this actual scene? Even the Nikon's better results at 70mm were just at the very edge area. Going inward just a little, and the two are quite similar. Remember-this is a very extreme blowup and I think even this difference will be unnoticeable in normal size viewing. And not to forget- the DA 12-24mm is wide open at f/4 so with any of these 24-70mm f/2.8 lenses, there will be some improvement at f/4.
