[stevebrot]

Hi thepavuk
Good news bad news: you are not alone!
I have exactly the same problem, no way to make the 50mm focus (single spot, AF mode s) on anything in quickly. I thought my model had a problem (it was a reconditioned on amz) so I changed it for another (also reconditioned) but the issue remains.
It looks to me as if this lens is not usable in any other mode than manual with the k3.
To note: I do not have the same problem with my other lenses in the same conditions (tamron 18-250 and Pentax 18-135) so to me the problem lies in the lens, not the camera.
I'm thinking about giving up on this lens despite all the "plastic magic" I read everywhere :'(

Strange you should have this problem. My copy of the DA 50/1.8 works great on the K-3 meaning that auto focus is fast and precise and accurate out of the box. Mine came new with the camera. In low light, performance is the similar to my other AF lenses. After all, it is the camera that does the focusing, not the lens.


Steve

[screwdriver222]

I don't have the DA 50 but I am pretty sure I have heard of some people experiencing af problems with it. so I would check the camera out with a different lens. My K3 works very well in low light with all the lenses I have.

Jeff

[stevebrot]

I don't have the DA 50 but I am pretty sure I have heard of some people experiencing af problems with it.

Care to share? I am pretty active on these forums and the above post (#15) is the first complaint I remember for the AF performance of the DA 50/1.8. The OP's problem was with both lenses owned, not just the DA 50/1.8 and the blame was not pinned on either lens.

Your suggestion regarding a different lens is a good one in general and would rule out a bad copy of the DA 50/1.8. As for the DA 50/1.8 being generally or frequently problematic...I guess you can only speak from experience for a lens you have experience with.


Steve

[screwdriver222]

Care to share? I am pretty active on these forums and the above post (#15) is the first complaint I remember for the AF performance of the DA 50/1.8.

Check out the lens review section on this site.

Jeff

[stevebrot]

Check out the lens review section on this site.

Jeff

I based my earlier statement on the eerie lack of AF rants for the DA 50/1.8. I do believe that it is quite possibly the most generally acclaimed lens released during the 7+ years I have been active on this site. I can think of only two other recent lenses that are as well thought of (DA 15/3.5 Limited and DA 35/2.8 Limited).

I am also familiar with the reviews for this lens*. In regards to the reviews, did you read the comments and also note the rating given for the reviews where AF was mentioned as a con? To be honest, I don't see a pattern of poor AF performance specific to that lens. The complaints are rather generic and of the sort generally related to the AF system and not the lens.

Here is what I found:

• 4 of 32 reviews were critical of the AF performance
• Of those four, the AF scores (total score in parentheses) ran 7(10), 5(8), 9(10), and 8(10)
• Average AF score for all 32 reviews: 8.4 (9.31). 8.4 is typical for screw drive Pentax primes.

Complaints are:

• Hunts (3) (K-30, K-x, K10D/K-30)
• Fails to lock (1) (K10D/K-30)
• "steps off" (1) (K20D)
• "wobbly" (1) (K20D)
• "fails to track in AF-C" thought might be body issue (1) (K20D)

At this point it might be good to make a note regarding "hunting". Pentax AF strategy is biased in favor of accuracy in AF-S mode. A final step check is done which in dim light or low contrast can result in a little two-step at the end. This is not the same as full-rack hunting. A tendency to hunt is usually an indication of poor contrast or lack of sharpness wide open. Low light or poor subject contrast may also cause hunting.

I would be the last to say that the DA 50/1.8 is free of issues and the first to suggest that poor performance is likely due to some flaw in manufacturing or design. Hunting may be the result of poor mechanical tolerances in the lens reviewed and makes me wonder about the innards of the lens.


Steve

* I should probably add a review of my own since it is one of the few lenses on my shelf that I have not reviewed here.

[Flugelbinder]

To the OP:
I have been having an issue, in a way similar to yours, though not exactly the same. Solution? Try to stop down the lens and see what happens... If you shoot other than manual, try aperture priority and set the lens to 2.8. Let us know...

Kind regards.

Paul

[idomenee]

Hey all,

I think I better understand the issue here.
To recap:
- I have my old faithful K10D with a 18-250 Tamron lens (autofocus is screw driven)
- I bought the K3 (recondittionned) with both the 50mm (screw) and the 18-135 from Pentax (motorized)

I tried all the combinations and ho and lo, here is what comes out of them:
- any lens on the K10D works fine
- the 50m and the 18-250 on the K3 cannot focus (really cant), but the 18-135 works like a charm

My hypothesis: my K3 has a problem using screw-driven lenses

Maybe that is also what happened to you?

I sent it back to Amazon and am waiting for a new one. Crossing fingers

[stevebrot]

I sent it back to Amazon and am waiting for a new one. Crossing fingers

Let's hope you have better luck with the next one.


Steve

[idomenee]

Hey all,

just to let you know, changing the body of the K3 solved everything indeed
now autofocus works as a charm with all my lenses, fast and seems precise, both with motorized and screw-driven lenses.

So it was indeed a body problem, specially linked to the focus screw



Now I just have a newbie question:
when using my tamron 18-250 to shoot wide to normal angle, I would first zoom to 250, make my focus on the subject I wanted, then zoom out while maintaining my finger on the button, frame, and then shoot. The focus distance/point would stay the same.

It still works with this lens and the K3 instead of my K10, but curiously it doesnt work with the 18-135 from pentax: if I zoom out or in, the camera changes its focus distance, and I have to re-focus with my final framing.
Anything that could explain this? Another thing linked to motorized vs screw-driven (I could imagine this having a link to that)? some parameter I should configure?

Thanks for your answers

Ido

[Flugelbinder]

The lens has to be parfocal in order to do that...

[ongaku]

Not all lenses keep focus when zooming in or out.

[awaldram]

From the first photo (IMGP1004) the EXIF shows Focus Mode: 'Manual. So what is the problem here. I can see areas in focus, but it seems like the subject is tilted at perhaps 45 degrees. It also shows that you have AF adjustment of [+2] active.

With the blue bag (IMP1007 - 50mm, f/1.8, 1/60s @ ISO 3200, PENTAX K-3) you were shooting wide open at a target with few distinct contrast edges, and wide-open your DOF would have been very narrow. You were shooting using the AF mode 'Zone Select Centre - Select Single Point', and had selected the single centre point, which the camera says it achieved focus on. It's hard to see from the dull image if the centre point is in focus or not, as there seems to be some motion blur in the photo. And AF adjustment shows [+2].

The picture of the cat (50mm, f/1.8, 1/100s @ ISO 1600, PENTAX K-3) is also 'Zone Select Centre Single Point', and EXIF says focus was indeed achieved on the centre point. Here you can also see the very narrow plane of focus of shooting wide open. There is a 3 or 4 cm wide band of the animals fur that is indeed in focus along the centre point of the screen. And in this image, now the AF adjustment is showing up as [-2], whereas in other images it was showing up as [+2] for that lens.

The EXIF for the photo of the cupboard (18mm, f/10, 1/4s @ ISO 6400) says you were using centre single-point AF and that the AF achieved focus on that. When you look at the image, that seems true. The back of the screws seems to be in focus. But shooting 1/4 second handheld isn't ideal for sharpness. Here AF adjustment is indicated as [0].

As far as I can see, some of the issues with the above sample images are more to do with shallow DOF, motion blur and incorrect AF adjustments. I suggest testing your AF on more precise, flat targets before concluding that something is wrong with the camera.

I'd also add using shallow DoF if AF adjustment is mis-set the camera will struggle to find focus lock irrelevant of light levels.

---------- Post added 24-12-14 at 10:24 AM ----------

Hey all,

just to let you know, changing the body of the K3 solved everything indeed
now autofocus works as a charm with all my lenses, fast and seems precise, both with motorized and screw-driven lenses.

So it was indeed a body problem, specially linked to the focus screw



Now I just have a newbie question:
when using my tamron 18-250 to shoot wide to normal angle, I would first zoom to 250, make my focus on the subject I wanted, then zoom out while maintaining my finger on the button, frame, and then shoot. The focus distance/point would stay the same.

It still works with this lens and the K3 instead of my K10, but curiously it doesnt work with the 18-135 from pentax: if I zoom out or in, the camera changes its focus distance, and I have to re-focus with my final framing.
Anything that could explain this? Another thing linked to motorized vs screw-driven (I could imagine this having a link to that)? some parameter I should configure?

Thanks for your answers

Ido

Neither lens is parfocal (usually a high end feature think da*50-135) but the tamron :250mm is f6.3 so when you zoom back your image may remain within the DoF and look OK or the Tamron is less non-parfocal then the Pentax

Either way the technique your using is not appropriate for the lens you have if you want sharp images

[idomenee]

Thanks a lot for your answers!
I was inded unsure it was a usable technique, but it seemed (on the lcd screen at least) that the focus was more precise this way.
Now when the images finally arrived on a big screen, they would indeed sometimes be slightly out-focused.

So to sum it up: I should choose my appropriate zoom level, and then focus and shoot without changing it, right?

Last (but not least, i'm taking the plane tonight) question: Have you seen a benchmark in terms of image quality between those two lenses? (18-250 tamron vs 18-135 pentax)?
I tried to do some comparison today and it seems to me the tamron has
- bigger zoom (obvious)
- better sharpness at 250 and 135mm when subjects afar (comparison on the lcd screen of the camera, zooming to the max)

while the pentax has
- weather resistant body (also obvious, and this is the reason i bought it in the first place)
- better sharpness when subject is mid to close range (even zoomed to 135mm)


But somehow it doesn't seem logical that a 8yo lens from tamron would produce better images than a brand new pentax lens with about the same price
So, maybe I'm doing it wrong

Which one of the two would you advise taking if you had to take one.
Note: I also have the 35mm and 50mm plastic pentax lenses that i never tried yet
Note 2: i'm going australia / new zealand