24-70 II Corners

[extremeinstability]

I'm just wondering if this should be expected for corners at 50mm and 70mm at F4 with this lens full frame.

http://www.extremeinstability.com/2470-50-f4.jpg
http://www.extremeinstability.com/2470-70-f4.jpg

Nice and crisp in the middle but goes pretty damn crappy up and away much while not at the 24mm end. Never used a good standard zoom on full frame till now. I'm probably expecting too much from a zoom on full frame. Or this is a bad copy, which sounds there have been plenty of. Really don't know.

Thanks

 

[extremeinstability]

Nevermind, determined it is all field curvature. Takes a ton of stopping down to get them worth anything in the 50-70mm range.

 

[BozillaNZ]

Glad you found out the issue. Top quality zooms can now rival primes in terms of sharpness, contrast, color and even bokeh, but there are two thing they can't do well yet: Distortion and field curvature.

If the field curves towards you in the corners, try to focus the lens at infinity and stop down, you will get better overall sharpness than let the AF dial in or using hyper focal distance.

The 16-35 II have complex wavy field curvature. Lots of people saying that this lens has so called "mid-field-weakness", which means the center is good, then goes bad in mid-field, then better at the corners. However this is the same as what you discovered above: field curvature at it's most evident term. Manually focusing 16-35 II to infinity and stop down to f11 and it becomes sharp corner to corner.

 

[extremeinstability]

Yeah I don't get how one would get good results if they shoot it wide open even at infinity if they are all like this. Couple examples at 50mm F4.

http://www.extremeinstability.com/2470-50-f4b.jpg
This one the top crop is from the middle..sharp. I then simply reframed the shot, same focus and put it in the corner.

http://www.extremeinstability.com/cornerfocus.jpg
And this one is opposite. I used the corner to focus with live view 10x(did that in center on first one). I took the photo with it in the corner and it is sharp out there. I then reframed that area to the middle which is the lower crop.

One should be able to shoot wide open at infinity and get something worthwhile out there, but least in the case of this one, it's not even close. It probably has some element being off making it worse or something.

 

[Mt Spokane Photography]

As you can see in the photozone test charts, extreme corners fall to the merely "Good" range when the lens is wide open.

Zoom lenses are always a compromise, in fact, all lenses are a compromise. A better lens can be built, but the price and weight might take your breath away.

Most photographers won't pay $60K or more for a step up in corner quality.

 

[extremeinstability]

Well at infinity in the mid-ranges it's not extreme corners and not even close to ok. If one wants to save the corners with this one it seems you'll have to focus a bit past center's infinity and sacrifice the middle some. Here is a 50mm example at F4.

100% crops. Number 1 is from the center and 2 with it reframed to the upper left corner....so that closer tree is actually even further out in the frame. Yet once it is in the corner the closer tree gets better as the further stuff goes to hell. The field curvature is just bending back towards the camera a good bit. Does it both sides like that and from other reading it sounds like just design related.

http://www.extremeinstability.com/1.jpg
http://www.extremeinstability.com/2.jpg

But again, on number 2 that is the furthest upper left corner. The tree is pretty dang great for extreme corner, but alas infinity areas have gone to hell out there. If you focus using the corner out there you can pull them in good but you then sacrifice the middle sharpness.

Starting to think this lens isn't out of whack and that is just how it is using it at infinity.

More talk on it here: http://www.dpreview.com/forums/post/52164436 THink that was the place I saw someone setting their afma purposely off a hair to help the corners.