RiceHigh's Pentax Blog: Image Corner Blur Issue with K-3 III (Head-to-head Comparison with KP)

Saturday, June 12, 2021

Image Corner Blur Issue with K-3 III (Head-to-head Comparison with KP)

Have had my K-3 III for over one month now and tested it with my various DA/FA/DFA lenses (mostly primes) but there is a strange issue discovered.

It is all about the unexplainable corner (or simple off-centre) softness in the images taken with the K-3 III. To illustrate the problem, here we go with the sample set below, with a pair of images taken using my K-3 III and KP with the same lens (which is a HD-DA 40mm Limited), at almost the same time and with the same exposure parameters.

Let's see the 100% centre crops of the pair of images, which are perfect in focus. I captured also the EXIF data on screen for our easy reference (Click pictures to Enlarge):

Then, here are the left side of the images in 100% crops:

And then, here are the right side of the images in 100% crops:

This problem really drives me nuts. I really didn't expect the new flagship camera would produce much lower resolution at off-centre in images than its predecessor model of 2017. It's really much frustrating after all.

It seems that the new sensor of the K-3 III has some kinds of incompatibility with the existing Pentax lens lineup optically, which is a hardware issue but not a software one, I believe. Note that I had already turned off all the lens correction functions as well as the AA filter simulator to rule out the possibility of the issue is being caused by software or other factors.

Comments (19)

Logging you in...

Dashboard | Edit profile | Logout

Logged in as

+1 Vote up Vote down

RiceHigh 110p · 197 weeks ago

It also seems that this problem is less dominant for shooting close objects than landscape.

0 Vote up Vote down

Thomas · 197 weeks ago

It could also be that the focus (AF) is not aligned well,needing an adjustment. So,it's a bit off,but you still get sharpness in the center due to DOF (you know,the DOF is not the same all over the sensor area,i.e. it's wider in the center).

1 reply · active 197 weeks ago

+2 Vote up Vote down

RiceHigh 110p · 197 weeks ago

Not really, the focus was confirmed dead on even when the lens was wide opened.

0 Vote up Vote down

ToetSFX · 197 weeks ago

Unfortunately I can't add anything to this. I don't have the technical knowledge. But the examples seem to speak for themselves. How extremely bizarre... Is this also the case with other (prime) lenses? I am not (yet) a K3 III owner / user....

1 reply · active 197 weeks ago

+2 Vote up Vote down

RiceHigh 110p · 197 weeks ago

I tested also DA15/21/35/35 Macro Limited lenses, they all showed and suffered from the same problem with the K-3 III. They were needed to stop down to f/11 before the effect diminished. It is also noted that wide angle lenses are affected more than longer focal lenses, as I tested primes of 50mm and longer and they seemed to be ok.

0 Vote up Vote down

Tjompen · 197 weeks ago

Do you have horizon correction turned on or off?

5 replies · active 196 weeks ago

+1 Vote up Vote down

RiceHigh 110p · 197 weeks ago

Not turned on by default.

0 Vote up Vote down

Tjompen · 197 weeks ago

The horizon correction has shown to create soft corners when used together with 2s timer. Maybe it is creating some kind of weirdness when used otherwise also. I reacted yesterday to soft corners on one image and I could not understand why. Will test again.

+1 Vote up Vote down

RiceHigh 110p · 196 weeks ago

I took my pics handheld with a high shutter speed and horizon correction was not enabled.

0 Vote up Vote down

Tjompen · 196 weeks ago

Ok, I will do some similar testing when the light gets better. I did a test with K-1 in crop mode and K-3 III using my FA43@f/4 and 8. They look similar. But yesterday I took some images and found exactly what you have found...

+3 Vote up Vote down

RiceHigh 110p · 196 weeks ago

Indeed, I am almost certain that it could happen for any K-3 III.

-1 Vote up Vote down

mtkeller · 196 weeks ago

You haven't convinced me that this isn't a focus difference. I don't have any wide angle shots below f/8 with the K-3 iii sitting in my catalog right now, other than Milky Way shots, but I might have a vantage point where I could do some similar testing. If you're using AF, it's very much possible that the cameras are selecting a different distance at which to focus, rendering the full scene in focus on the KP and less than the full scene in focus on the K-3 iii at f/5.6. At the distance you're shooting, there will be a range of focus distances that get you center sharpness in the OVF, so saying that the focus was dead on wide open doesn't mean a lot here.

3 replies · active 196 weeks ago

+2 Vote up Vote down

RiceHigh 110p · 196 weeks ago

I had also focused with Live View at Centre and Off-centre but with no luck and got the same results.

0 Vote up Vote down

mtkeller · 196 weeks ago

So what happened when you focused at the point off-center in live view? Were you able to get something that looked in focus in live view but the image captured didn't match or weren't you able to get the off-center spot in focus?

+3 Vote up Vote down

RiceHigh 110p · 196 weeks ago

The focus shifted a bit when I focused off-centre in Live View but that didn't change the results by much. I may post again later to show the pictures taken with my DA 21 Limited on my K-3 III, against on my KP.

0 Vote up Vote down

alexk · 196 weeks ago

K3 III is all about the new vastly improved AF, so chose your poison carefully, it's either a corner smearing or K3III AF being a total crap, worse than of the KP.

So which is that?

2 replies · active 195 weeks ago

-1 Vote up Vote down

Derek · 195 weeks ago

"AF being a total crap" may be not unlikely? DPReview TV said, the AF is "consistently" worse than the 5 years old and cheaper Nikon D500.

+3 Vote up Vote down

RiceHigh 110p · 195 weeks ago

How "worse" it is?

0 Vote up Vote down

david · 192 weeks ago

I haven't heard of that issue and corners look so crap that I can't believe nobody noticed it before. If yours lenses were fine on you older bodies, and if all lenses show the same issue with K-3III, may be your copy of K-3III has misaligned sensor or any other issue? Have you tried to send it back for exchange?

Post a new comment

Comment as a Guest, or login:

Tweet this comment

RiceHigh's Pentax Blog

Saturday, June 12, 2021

Image Corner Blur Issue with K-3 III (Head-to-head Comparison with KP)

Forgot password?

Comments (19)

Post a new comment

Reference Links (by Others)

My Technical Articles (Latest First)