[semaca]

I'm using a K-3 and 18-135 and I always had sharp images with this lens, but something is not right now. Recently I did some small cleaning to the sensor, but I don't think that is the reason of soft images and also not the diopter.
I know that at the wider angle it's not brilliant, but everything looks blurry. Or maybe I'm exagerating.

18mm f/5.0 1/125s ISO400

Any advice?

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Last edited by semaca; 04-05-2017 at 10:14 AM.

[Na Horuk]

With Autofocus the image edges seem to be sharp. So I assume you have some back or front focusing. Live view uses a different AF system, which doesn't suffer from front/back focusing.
a) Possibly the camera used a wrong AF point. Check AF point settings.
b) Possibly the camera is too close to those flowers and the minimum focus distance simply cannot reach it. Probably not the cause in this one, since live view AF could reach it. Unless the camera was moved a couple cm between shots
c) Maybe you had AF fine adjustment enabled but it somehow got reset; or maybe you did not have it enabled and it was fine, but now it is enabled and is causing problems. This would affect normal AF, but not live view AF

Don't know what else could be the problem. Was the lens damaged, dropped? Are the lens and camera mount free of dirt and damage?

[semaca]

It was on AF-S with the center spot. AF fine adjustement is off, I don't really know how to use it. The lens was not dropped but if I want to clean the mount/contacts should a use something special or just the normal stuff for a lens?

[stevebrot]

It was on AF-S with the center spot.

Too bad the image is cropped. As a result it is difficult to determine the intended point of focus. From what I can tell, the intended point of focus was at or near ground level; either that, or you have some pretty intense back focus going on.


Steve

[semaca]

Too bad the image is cropped. As a result it is difficult to determine the intended point of focus. From what I can tell, the intended point of focus was at or near ground level; either that, or you have some pretty intense back focus going on.


Steve

I'll try to add another image tomorrow. It should be something like a cityscape or a closer object? That back focus thing doesn't sound too good and I really need the camera in the weekend

[semaca]

The results with the autofocus are all over the place. I have tried to use fine adjustment with +/-. but I don't see a diference. How come that can of paint be so out of focus using just the autofocus?? The messy stuff is mostly at 18mm, but seems sharper at a bigger focal lenght.

[ZombieArmy]

Yeah your lens has some bad back focus.

[Na Horuk]

I'm using a K-3 and 18-135 and I always had sharp images with this lens, but something is not right now.

The surprising part is that it used to be good. Sometimes a lens can have a problem, but its usually either already present when you get it, or it develops after some shock (bumpy travel, a fall, ...)
How does the focus ring turn if you switch to Manual focus? Does it turn smoothly, or are there odd resistances at some points?

You can search the forums or on blogs about how to use the focus fine adjustment correctly. Often people use some sort of focusing chart.
If adjusting for backfocus doesn't work, then the lens might have some other problem. Ideally you would test this lens on some other camera, just to pinpoint the issue. Is the lens still in warranty? I recommend you write a report about your experience to the repair shop

[semaca]

How does the focus ring turn if you switch to Manual focus? Does it turn smoothly, or are there odd resistances at some points?

If adjusting for backfocus doesn't work, then the lens might have some other problem. Ideally you would test this lens on some other camera, just to pinpoint the issue. Is the lens still in warranty? I recommend you write a report about your experience to the repair shop

The focus ring seems to work normal.
So, for backfocus I should adjust it with +1 and check it, or +2 if that's not ok. That if is not a front focusing problem?
I think that the warranty was for 2 years and maybe just ended a month ago, but I have to search for the papers.

[Na Horuk]

I think that the warranty was for 2 years and maybe just ended a month ago, but I have to search for the papers.

Did the problem start before the warranty ran out? Maybe you can make a case for a free repair, or at least some discount on the repair. Really depends on your local shop

[emalvick]

So did you say you don't have a problem when using Live View?

You also said this happened after cleaning the sensor. I wonder if this is a problem with the body and not the lens. Have you tried another lens to see if you are having the same issue?

At wider angles, I think auto-focus can be difficult because the auto-focus points are not as small as we all expect them to be. It becomes very easy for the camera to focus on something in front of or behind an object if the object isn't very big. I've had that problem often with my Pentax cameras and wider angled lenses.

The best way to test and adjust for back/front focus is to use a tripod and a more calculated target. The paint can is a good idea. I usually use a ruler/yard stick with a distinct mark I can focus on.

The difficulty with a zoom lens is that adjustments are for the lens no matter the focal length, so if the lens is working fine at the telephoto end, it may not after you adjust it.

[35mmfilmfan]

The difficulty with a zoom lens is that adjustments are for the lens no matter the focal length, so if the lens is working fine at the telephoto end, it may not after you adjust it.

If this is so for a particular lens, would you advise making the correction for the telephoto end of the zoom, and trusting to DOF to take care of the wide end, or am I missing something ?

[kh1234567890]

but something is not right now. Recently I did some small cleaning to the sensor

Any dust/dirt on the AF sensor ?

[semaca]

Any dust/dirt on the AF sensor ?

To be honest, I don't think I know where to look

Too bad that the 18_135 is my only lens with autofocus. I did a small adjustment but the results are not very clear.
For a wider scene what is the best setting? Single point AF.S?

[stevebrot]

Here are a few hints:

• When evaluating focus issues, make it easy for the camera to do its job
• Use a flat, high contrast target in good light, sensor parallel to target
• Use center-point (spot) fixed AF point and know where it is pointed
• Use a tripod, SR off
• Avoid curved surfaces*
• Avoid receding surfaces
• Avoid low contrast target
• Remember...the camera has no clue what you intended as point of focus
• Use magnified live view as your point of reference to PDAF

On your example photos, it is not clear where the intended point of focus and whether the active AF point was at that point.


Steve

* The front of a can such as one of your examples can be used, but the size of the "patch" with adequate DOF must be larger than the AF point and the point must be centered at the peak of the curved surface.