rf 16mm 2.8 - Raw Images (Normal Distance + Closeup)

crusliq wrote:

I added some pictures with different focus distances (13cm, 15cm, 20cm, 50cm and 120cm).

For me it seems to get ok at 50cm and then good at 120cm.

Thanks.

Looking at the images they are a mess in the corners at 13cm. Even at f8, the image looks pretty messy in the corners. While they get "sharper" at f8, but it looks like there are double images in the corners. As I wrote before, not many people are using a wide-angle lens from 13cm.

At 50cm the lens is becoming "well behaved." It is soft in the corners (and interestingly just a tad soft in the middle with a donut hole in the focus) but sharpens up nicely by f8.

By 130cm (just over 1 meter) it behaving well.

Something else that was striking when I stacked all the original images in Photoshop is the amount of vignetting at f2.8 vs. f8. It seems like whatever settings were being used, it is under-compensating for the vignetting.

Below I have run Photoshop Find Edges on the various images. With this test, darker=sharper (of course is it content-dependent too). This is not a perfect test but it gives a feel and some objectivity for how the sharpness is varying. The nice thing about your pictures is they had lots of small random detail which can be exploited by Find Edges. I find it helpful to look at the Find Edges and then go back to the original photo and see how they correlate.

NOTE: Ignore the EXIF information on the photos. I stacked the images in Photoshop and then did a Save Layers. When you do this all the images get the same EXIF.

13cm f2.8 Find Edges

While at F8 the Find Edges makes it look like it is sharp. But looking at the original image, these "edges" look like they are double images.

13cm f8 find edges

Definitely looks much better at 50cm both in the picture and at f2.8. It looks like there is a "donut hole" in the focusing where there is a ring (dark area in Find Images) around the middle that is sharper than the center.

50cm f2.8 Find Edges (note a bit of a donut hole)

At 50CM and F8 the donut hole fills in and the sharpness looks uniform. I consider this "well behaved" in that stopping down makes the image better.

50cm f8 Find Edges. Note donut hold fills in at F8 and overall sharper. You can see a center darker circular area of sharpest focus.

By 120cm, there is not a huge difference in sharpness at f2.8 and f8. At f8 gets a bit crisper in the far corners and the central zone of the sharp area expands.

120cm f2.8 Find Edges

120cm F8 The dark (sharpest) area in the center expands and the corners get sharper. Compare the brick in the lower-left corner at F8 and F2.8.