24-70 F4 blows away my kit lens

Started Mar 2, 2014 | Discussions thread
Fred Briggs
Fred Briggs Senior Member • Posts: 1,023
Re: 24-70 F4 blows away my kit lens

GaryW wrote:

Fred Briggs wrote:....

In fact there is only one plane which is actually in focus - everything in front and behind that is out of focus to varying degrees, depending on how far from the actual focal plane it is. DOF just reflects how much "appears" to be in focus if viewed small enough, or from far enough away.

Don't forget that often the focal plane isn't flat but curved. This makes judgements about "soft corners" a bit more problematic, particularly when examining photos of brick walls.

You can confirm this with a simple experiment. Take a picture of a brick wall at about 45 degrees,...

Yes - I didn't want to complicate things further by mentioning that, but it becomes significant when for example taking brick wall shots to compare edge and corner lens sharpness with central sharpness.  These kind of shots are often taken from close range and the error due to focal plane curvature can be very significant, but is probably a worst case compared to normal use.

If taking wall shots, it is interesting to take additional shots with the focus point near to the edge of the frame.  If this shows improved sharpness at the edge and a bit worse at the centre compared to a shot focused at the centre,  then it is a good indication that field curvature is present, though this may not be a big problem in real world shots.


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Gary W.

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"We are so small between the stars, so large against the sky." Leonard Cohen c1967

 Fred Briggs's gear list:Fred Briggs's gear list
Sony a6000 Sony E 55-210mm F4.5-6.3 OSS Sony E 10-18mm F4 OSS Sony E 16-50mm F3.5-5.6 PZ OSS Sony Vario-Tessar T* E 16-70mm F4 ZA OSS
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