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09-01-2014, 12:52 PM   #1
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Autofocus issues in low light

Hi,
first, I apologize for my english and words filled with anger and despair.

I've just bought K3 (DA18-135wr, DA50mm f1.8, fw1.11) and I'm really really dissaponted with AF, especially on lower or artifical light. Anybody have same problem?

I've tested nikon D90 and D7000 in same conditions, on same spot, with lenses on same focal lenght, same focus modes and my k3 is so terrible compared to them. Nikons focus on white wall, wooden doors, dark corner of my office without any problem in 1 second with 100% accurancy. Just press and it's focused. K3 at absolutely same condition keep moving from extreme to extreme and when I'm lucky, after 4-6 seconds it get focus, but in about 8 of 10 atempts, it wont. Even on easy patterns it's unsure. I get focus, move few cm left, then press AF button and it 5 moves front and back to get focus.

AF in Livemode is even worse. When I focus on some point and I press focus again, It focus to maximum front and then back. Slow as hell. On the other hand, when it get in focus, it's accurate.

At good light, outside, there is no problem. Problem is inside area with less light. Multisegment is usually better than spot, but it won't focus on places where I want.

I've uploaded 4 ugly, in rage made random test photos (1-3 artificial lighting, 4 daylight).
1) wall - forever problem. K3 wasn't able to focus. Photo is from manual focus. D90/D7000 no problem.
2) focused on third attemt which took few seconds
3) K3 focused but it took may be 4-5 seconds.
4) This was made on multisegment focus on may be 4th attempt. D90/D7000 get it instantly on spot focus. K3 won't. Another problem for K3 is pattern of that cabinet. Nikons get it instantly on spot, K3 never.

I've played with K3 while I wrote this and the sound of $1900 gear focusing front and back, front and back, front and back, front and back while I want to focus on my sleeping cat (photo 3) makes me absolutely crazy. It reminds me my old phone with AF. My latest phone focus faster then K3. I've bought K3 because there was soo good reviews about... everything, especialy great focusing in dark. I'm thinking about returning it, but is that problem of K3 or just my piece. I've bought batteries, lens, flash and I won't return it. If I send it to reclamation, I'm affraid that they say it's "in factory limits" as usually. I have 8 days to return it.

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09-01-2014, 02:00 PM   #2
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I have no idea what the problem is because my K-3 + 18-135 combo focuses in almost pitch black, it is spot on most of times. A white wall can be a problem but the other subjects you have shot should not be a problem.

Either you have set your camera wrong in some way or you are doing something wrong or there is something wrong with the camera/lens.

Reset the camera and test again. Make sure you select spot focus and AF.S.

You say live view also sucks, that makes this problem more strange...
09-01-2014, 02:41 PM   #3
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Thank you for answer.
I have two lens, booth acts same. When I look in settings, everything is in default mode. I didn't changed anything important. I'm sure that I use AF.S. I can try reset, but I've reflashed firmware two days ago so it should be reseted. That wall can be sometimes focuset in multisegment, but Nikons take it even in spot without problem, so I would expect that if six years old D90 can do that, new K3 should too. I will have to make some videos how it acts.
09-01-2014, 03:38 PM   #4
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QuoteOriginally posted by ThePavuk Quote
Anybody have same problem?
No. I have been consistently amazed at the low light AF capability of my K-3. While I have not done any personal comparisons, it is my understanding that the K-3 is one of the best on the market in low light. My K-3 will AF (PDAF) in situations where I can barely see the subject in the viewfinder.


Steve


Last edited by stevebrot; 09-01-2014 at 03:44 PM.
09-01-2014, 04:07 PM   #5
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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.

Last edited by rawr; 09-01-2014 at 04:15 PM.
09-01-2014, 04:16 PM   #6
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That sounds like I really have bad piece. I was suprised that nobody wrote about same issue on whole internet. Focus in dark was one reason why I bought K3 even that it cost 1/3 more than I wanted to put in DLRS. Typical for me. If you put one single chair with broken leg in IKEA warehouse, gues which one I will buy.
I have to test it more and then probably return it (I've bought it with 10% discount from internet shop, nobody sell set with 18-135wr in my town Damn, I have some events in next two weeks, where I wanted to make shots. If I keep it and send it to service later, I'm sure that they will say It's ok. 100% chance with our warranty services.
09-01-2014, 04:18 PM   #7
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I have re-read your message and have the following observations regarding AF evaluation:
  • Use AF-S and center focus point for all cameras*
  • Be sure AF-S is set for focus priority
  • Give your camera something to focus on*
  • Do your tests and comparisons at a fixed distance (on tripod) in full-spectrum light (Very few people are completely sway-free)
  • Flat target parallel to camera focal plane
It may well be that your camera and/or lens is defective. It may also be that your preferred choice of subjects are better served with the Nikon product. Since you already own the 18-135 in Nikon F, I would suggest that you might save yourself a few dollars and swap your K-3 kit for a D7100, body only.


Steve

* It is nice to think that a blank wall similar to your example above is a good test of the AF system, but it is not. For a truly uniform surface, no PDAF or CDAF system will be able to acquire focus. In the case of your wall, there is texture, but the distribution is somewhat scattered. Performance with that target will depend on the size (degrees of arc) of the AF point and where the camera is actually pointed.
09-01-2014, 04:52 PM   #8
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2 Rawr:
First, thx for analyse. Yes, these pictures are not great sample. I've spend hours today trying all AF modes on different scenes, turning on/off SR, AA etc. Nothing changed, where K3 failed, nikons successed. First 3 images was made with DA50 F1.8. When I tested it with nikons, I had 18-135 and checked settings if they are same. I adjusted AF to +/- 2 only on may be last 10 pictures (3 of them are here) as last hope before I started to write this topic. I wanted just to show on which textures and light scenes it have problem.

1st picture) As I wrote. was with manual because in AF it is not able to focus. Even before I've adjusted AF. I've tried to focus on that wall or wall in my office (better lighting, similar texture) for many times before.
2th, 3th picture) I know that it has short depth of focus so it's blured, that is not problem. Even if it is blured because I've incorectly adjusted it to frontfocus. Problem is that it took about 5 attempts which each took few seconds before I finally get focus and same situation was before I adjusted AF. Problems with AF in live mode made me to try adjust it.
4th picture) This picture just shows area where I tested it and compared to nikons which didn't failed single time whilest k3 almost everytime.

May be it sounds chaotic. It was, and now It's 2AM here and I have 3rd coffee inside me in last 4 hours..

09-01-2014, 04:55 PM   #9
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In low light, it also helps sometimes to set the camera to automatically use all 27 or 9 focus points. Let the camera decide in low light which AF point to use.

Outside of controlled testing, in real-life low light use single spot AF can cause the same troublesome issues as single point AE metering. The very small and specific single focus point selected may be trying to work on a tiny dark or low-contrast area of the scene, whilst right alongside it may be a nice contrasty edge it could be locking onto.

I just tried this myself, shooting a bookshelf with the lights turned off in the room. If I selected the single centre AF point to be the the only active one, the AF struggled because it was always finding some tiny dark spot to try and focus on. But if I selected Auto 27 or 9, the AF zipped straight into action and grabbed something on the same plane very quickly.

And I have to ask: are you using UV or 'protection' filters on your lenses Often they can cause problems with AF.
09-01-2014, 05:13 PM   #10
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2 Stevebrot:
1] "Use AF-S and center focus point for all cameras* - when I compared them, it was.
2] "Be sure AF-S is set for focus priority" - It was.

I didn't use tripod, but these nikons even haven't stabilisation and focused without problem. I've tried similar ranges and targets, tried different focal lengts. Yes, when there is lot of light and object is nice, it focus usually fast. The point is that it won't focus at hard conditions just searching front and back. Tripod would change nothing when I made may be 30 of 30 successful focuses on nikon targeting some area when with k3 at same place and similar focus lengh and only I hear is just brrrrrrr brrrrrrr brrrrrr from lens and see blinking green dot viewfinder in may be 29 of 30 attempts (talking about AFS, center focus mode).

I borrowed cam to my much more experienced colleges whose tried same things, and one told that it's terible for so expensive body and another one told that it's something wrong but he is not sure.
09-02-2014, 02:59 AM   #11
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I'm testing it with D7000 with 18-105 set lens and the difference is so huge that I cry inside me. D7000 focus faster and fluently, while K3 with 18-135 jumping front and back around spot. DA50mmF1.8 is even worse. I like that cheap plastic thingie, but focus is even worse than with 18-135. I wanted pentax for years, but now I will return it back. I like many features, awesome Focus peaking in live mode, stabilisation, buffer, speed, low lag and especialy WR. Damn, there is so many great things on this camera. But now, I'm disgusted how it acts when focus. I want fast device which I can trust. Not just for taking pictures of buildings and trees.
09-02-2014, 03:44 AM   #12
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QuoteOriginally posted by ThePavuk Quote
Resume
I'm testing it with D7000 with 18-105 set lens and the difference is so huge that I cry inside me. D7000 focus faster and fluently, while K3 with 18-135 jumping front and back around spot. DA50mmF1.8 is even worse. I like that cheap plastic thingie, but focus is even worse than with 18-135. I wanted pentax for years, but now I will return it back. I like many features, awesome Focus peaking in live mode, stabilisation, buffer, speed, low lag and especialy WR. Damn, there is so many great things on this camera. But now, I'm disgusted how it acts when focus. I want fast device which I can trust. Not just for taking pictures of buildings and trees.
Something is wrong. My K-3 focuses as fast and accurately in very low light as any camera I've ever put my hands on.
09-02-2014, 12:43 PM   #13
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I just want to say, that after all your recomendations, I will give k3 another chance. First I have to fight with (evil) shop where I bought this one and then I will probably take another one elsewhere. I just hope that you all are true.
09-02-2014, 02:46 PM   #14
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For reference, this AF guide is from Nikon, for the D4. The same issues apply to the K-3:



This is a map of the AF point coverage of the K-3, just to keep in mind:

12-19-2014, 08:34 AM   #15
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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 :'(
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