[Spotty Focus]

Firstly, Hi, and sorry for making my first post a question. Still, we all have to start somewhere.

I've had a KX for a long time (and a Pentax film cameras before that). I've never had really consistent results from the KX, possibly because I've only used the kit lenses and the 18-55mm isn't brilliant. The kit 55-300mm I have is a lot better IMO. I recently bought a 1" Canon compact for stuffing in a pocket whilst climbing mountains and found it took better images, which suggested it might be time to bite the bullet and replace the KX.

I found a bare K70 on offer and bought a 16-85mm lens second hand to go with it, as the range is just what I want for landscapes (although perhaps a bit heavier than ideal).


Unfortunately, that's where the problems start.

Although reviews suggest the 16-85 is pretty sharp across the frame, I've not been able to reproduce this at all. I've tried it on the KX and it doesn't focus in live mode, so I'm not 100% sure whether it is the (new) camera or the lens at fault, as it doesn't focus perfectly using the KX viewfinder. I've tried the kit 18-55mm on the new camera and it is definitely not sharp either, so I'm inclined to believe the problem is actually the K70, although I haven't really got a good place to test it formally.



The example below might suggest it is an angled sensor but other images are just a bit blurry on the left and not obviously near-focused. It does seem to be infinity focus that shows it at its worst though.

Any ideas where to start? I don't want to send the wrong item back.

Attached Images

 

[BigDave]

You may need to "calibrate" the lens to the camera. We expect to have this done right out of the box, but this is not always the case. There is technology within the camera itself to fine-tune the focusing so you get sharper images and more accurate auto focus/focus assist. Others can chime in here on this, and check your operations manual on how to do the fine focus tuning. I would be confident it is not the camera. Working with instrumentation over the years, I have found we people want to blame the device for the problems we see, when 99.9% of the time it is humans using the device that brings in the error!

Regards,

[Spotty Focus]

Thanks for the reply - I don't disagree about blaming the device. It is quite possible it is me. However, I've taken about 100 or so photographs and they are all a bit blurry, particularly on the left (whilst being OK in the centre). I've tried it both hand-held and with a tripod, and with live view AF and viewfinder AF (and MF). I assumed that live view wouldn't need calibrating?


I know you can adjust it for front/back focus for each lens on the K70 (this is much more difficult on the KX) but I'm not sure this is that? I'll have a look in the manual.

[hypermodern]

Can you post a couple more images? This one looks like the lens might be a bit decentred (plane of focus seems closer on the left than in the centre or right).

[Penview52]

The reason behind why the camera is sold at lower price is because the AF system is not working well with any lens. You have to try all test to get the correct AF or manual focus like changing all the AF active area, Link the AF active area to Customs settings and slightly rotate the tip of the lens after AF is done. Post a sample with exif data to see other parameters.

[ZeljkoS]

More images and with exif info would be helpful, this one is not enough to figure this out. Although it looks like focus is all over the place.

Try also with SR disabled, with high enough shutter speed. I found SR useful only in specific conditions (low light + static subject)... at least for how I use the camera. I don't have any long lenses.

[btnapa]

Any ideas where to start?

It looks to me to be a decentered lens. Return it if you can. Otherwise you have to send it to Pentax repair or a local shop that can fix the problem.

I only ran into this problem twice. More recently with a Samyang 14mm f2.8 for my Pentax system. One side was out of focus no matter how much I stopped it down. I bought it brand new so return was no problem. The replacement has no issues. As a matter of fact it is one of my sharpest lenses. The second time which was a few years ago, I bought a Tokina 11-16 f2.8 for my Canon system. I bought it used locally from an individual and the seller disappeared on me after the sale. Tokina promised to fix it. They did not do a thing with the lens and sent it back to me in the same exact shape and problem. Shame on Tokina!

For me, in more than 40 years of photography, the only manufacturer that has stood behind their products has been Sigma. They have fixed a few focus and firmware update issues for FREE! and with utmost professionalism. Well, the good guys list used to include Canon, but now they charge for all the service that I used to get for free.

[Spotty Focus]

Here's a couple of 50% crops (ie half size) of the left hand side of the frame. I'm not expecting edge to edge sharpness but this doesn't seem great. As mentioned, it is generally worse on the left, but I'm not sure in this case that it is just decentering.


I'll see if I can dig up an example from the 18-55mm, which I also struggled with. The light has been rather poor recently so I haven't had much chance to test in 'fair' conditions.

[jatrax]

I would suggest setting up on a tripod precisely square to a plain boring but well lit brick wall. Then you can really see what is happening. Landscape shots are nice but there are too many variables to really diagnose the issue.

As others have suggested it might be a decentered lens. But then again maybe not.

[Spotty Focus]

Sorry, one of those lost the EXIF data. The upper one was 1/80s @ 26mm, F5

I did try with SR / AS off and there wasn't much difference. I've tried MF, live view and normal AF and none gave what I would call satisfactory results. The original picture was taken using a tripod with 2s delay, BTW.


Many thanks for everyone's help.

---------- Post added 01-03-20 at 10:37 AM ----------

I'll try the brick wall test, although it seems to be infinity focus that is causing most trouble.

[MossyRocks]

In you second set of pictures the first image with the sheep seems to show the problem the best. where thing get gradually softer as you go to the left of the frame. This does lead me to believe that something is tilted. I would try other lenses to see if it is the lens or the camera sensor. Shooting more wide open will make the problem more apparent so is something I would do when testing things.

[Madaboutpix]

Normally, I would not be so quick to judge, ask for more and full-res sample shots, but here I'd say it's as clear as day: Someone has sold you a massively decentered lens. The left side of both sample shots looks as if viewed through a cola bottle. Return it, if possible, or have it competently serviced.

[pryorkshire]

As others have said there is definitely a problem, most likely with the lens. I also have a K70 and 16-85 lens and get pin sharp photos without any back/front focussing adjustment.

Print out a A4 lens focus test card, mount square to the camera and take a full frame shot, this will clearly show the out of focus zone.

[Bertrand3000]

I agree, the left part is always blurred, your 16-85 is decentered, it has nothing to do with the body (besides it is was the body, your Kx would not be affected). Return it, and if you can't, then bring it somewhere to fix it, it's something doable (but of course it will cost some money).

Not sure about the 18-55 though. You should know that there are five versions of the 18-55 but in reality only two optical formula. The first one is the DA 18-55 AL ; this lens is less sharp than all the other 18-55 with better optical formula (DA 18-55 ALII, DA-L 18-55, DA 18-55 AL WR, DA-L 18-55 AL WR). But of course, the first 18-55 is also the most widespread. We cannot exclude the fact that your 18-55 need focus tuning, so a different problem, but without test image we cannot say. Try your 18-55 in Live View, this will exclude any problem related to focus tuning. If it's sharp in Live View, then you only need to tune the 18-55 in order to focus correctly in viewfinder mode.

[mikesbike]

A 1" sensor is going to present a quite larger depth-of-field (DOF) at a similar aperture as that on an APS-C sensor, so more of the frame will appear decently sharp. This tends to make precise focusing less important.

In the top photo, focus is centered in closer to the foreground, so the grasses around the waters edge area appear to be more within the focus point compared to the distant shore and windmills. If you want to try to get both within the sharper focus range, you need to stop down the lens more to a smaller aperture (larger number) to increase your DOF. The above result brings the question as to what AF settings you are using? If you are using the default standard, with multiple AF points in play, the camera will choose which AF points will be favored, usually doing a good job, but with so many choices in the frame, might choose that which is closer to the camera.

In your set of two pictures, the top one being taken at wider angle has greater DOF, yet the focus point is again more in closer than central, which could otherwise include the distant scene. in this case, the camera's AF system did a good job, given the wider aperture with its lack of possible DOF, and as AF sensors are sensitive to higher-contrast objects, unsurprisingly latching on to the sheep. This worked out well, making this quite a nice photo. The extra contrast of the sheep was greatly helped by the coincidence of the sun peeking onto that portion of the scene, while the distant background remains under cloud cover. Nice effect! Even though the background is defocused, that greatly adds to the effect of the sheep standing out and being emphasized. Their being off to the side, while the treetop is also decently sharp, and more central, this makes for a well-balanced composition, with a good sense of depth. If everything had been sun-drenched and in focus, the result would look more flat and there would not be anything to lead the eye onto. Without seeing the whole frame since this is a crop- nice job of cropping!

As the 2nd photo of the set is a crop, I cannot determine where the camera's choice of a focus point might be.

In any case, you could use a center-only spot AF and by using the camera's half-press of the shutter button to achieve focus, you can train it upon whatever you wish to focus on, hold that with the half press, then rearrange your composition before releasing the shutter. This is the most accurate way of using AF

To check your lens against being decentered, choose a solid object, maybe a streetlamp post, with good contrast against a background (the sky?) Use the AF method as above. Shoot one with the object centered in the frame. Then by holding the half press and moving the camera before releasing the shutter, place the object near the right edge, then near the left edge, then near the top and then near the bottom edges. Do so at longest tele, then at mid tele, then at wider angle. All shots at maximum aperture for the FL (smallest number) to reduce DOF so only the object can be sharp. Either use a tripod with SR off, or if hand-held with SR on and plenty of shutter speed- 1/180 sec should be plenty since the lens only goes out to 85mm, but higher is ok too. If results look far off normal, repeat the test to make sure.

When you compare results, the sharpness of the object should be similar on the right vs. the left edge, and top vs. bottom. You can include corners also. Keep in mind, by and large, lenses are not generally as sharp at edges as centrally. But you can get an idea whether one side is far off the other.

For shooting top quality JPEG images, the K-70's processor is very good- just make sure to implement "Fine Sharpening" in the Custom Image menus, especially in the menu of the most-often used "Bright"category.