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05-19-2012, 02:38 PM   #1
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New K5 user (from D7K). Low light focus issues.

Hello all,

I am a new K5 user. I have had Nikons for as long as I can remember (D80, D90 and D7000). However, my D7K with it set of heavy lenses (including the 17-55 f/2.8) now seems a bit too heavy for what I want to carry around. I have long ached for a small lightweight kit. The Pentax system with its small primes seemed perfect. Nikon does not have anything that compares to the small pentax primes. So, recently, I bought a K5 and a couple of DA primes. I absolutely love the setup. The pictures are awesome and I feel like I am enjoying shooting again. I have had the camera for only a few days but I like what I am getting from the camera:

http://farm8.staticflickr.com/7096/7188895056_d42f7f76fc_b.jpg
http://farm8.staticflickr.com/7090/7228830358_a769946fef_b.jpg
http://farm8.staticflickr.com/7219/7229048386_7ac08cc36a_b.jpg
http://farm8.staticflickr.com/7223/7192863850_d47b084342_b.jpg

There is only one problem. In low light, AF seems to be a total hit or miss. I have thousands on pictures with my Nikon taken indoors in absolute darkness and AF has always been bang on. With the K5, indoor or outdoor pictures seem to front focus.

Here are some examples followed by center crops. I mostly use center AF point and recompose. Sometimes I will change the focus point to where I want the focus to be. In most of these I pointed at the face and recomposed.

http://photos.smugmug.com/photos/i-Prjjrck/0/X2/i-Prjjrck-X2.jpg
http://photos.smugmug.com/photos/i-XVMwscJ/0/XL/i-XVMwscJ-XL.jpg

http://photos.smugmug.com/photos/i-PKbxG6j/0/X2/i-PKbxG6j-X2.jpg
http://photos.smugmug.com/photos/i-dj72pd5/0/X2/i-dj72pd5-X2.jpg

http://photos.smugmug.com/photos/i-QVpJZNK/0/X2/i-QVpJZNK-X2.jpg
http://photos.smugmug.com/photos/i-hgvR3g7/0/X2/i-hgvR3g7-X2.jpg
Clearly FFed. The hand is in focus.

http://photos.smugmug.com/photos/i-dWH9cBL/0/X2/i-dWH9cBL-X2.jpg
http://photos.smugmug.com/photos/i-Z2qMcLW/0/X2/i-Z2qMcLW-X2.jpg

http://photos.smugmug.com/photos/i-gSJgcB7/0/X2/i-gSJgcB7-X2.jpg
http://photos.smugmug.com/photos/i-9xHzTzW/0/XL/i-9xHzTzW-XL.jpg

http://photos.smugmug.com/photos/i-9ND8chS/0/X2/i-9ND8chS-X2.jpg
http://photos.smugmug.com/photos/i-JBs34vj/0/X2/i-JBs34vj-X2.jpg
The glasses in front are in focus.

So what is going on here? I would love to the told that this is all operator error because I really want to keep the K5. But I have never had so many focus misses in my life.

05-19-2012, 05:44 PM   #2
hcc
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Thank you for the comprative comments. I fully agree your comments about the superb primes offered by Pentax: eg, the FA Lrd series, DA Ltd series, some FA* vintage lenses (FA*85mm), and many more. Your comment on weight is interesting. We take for granted that Pentax cameras have SR and the lenses are lghter.

In very low light, MF lenses are definitely a must IMHO. I shoot outdoor at dawn and dusk and my favourite lens is the VL58mm f1.4. It is MF and works great.

Another option with AF lenses is to pre-focus manually. It works nicely with lenses equipped with Quick-shift, but it works also with other (eg FA) lenses.

I add that I do not have experience with Nikon or Canon in low lights. I only speak from my experience with K-7 and K-01.

Hope that the suggestion may be of interest..
05-19-2012, 05:49 PM   #3
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I am by no means an expert on this topic. From what I have gleaned is the following:
  • Nikon and Canon have a better auto focus system than Pentax.
  • Pentax is based on contrast detection. As such in low light, you can have a lack of contrast, and thus auto focusing becomes very problematic.
  • Pentax also goes for focus accuracy. As such Nikon and Canon tend to lock faster (think of this as a single stage auto focus lock), Pentax on the other hand essentially has a two stage lock, fast "macro" that then defines a smaller range for the "micro" lock. When Pentax AF locks, it tends to have a higher accuracy rate than N & C. However, in that its somewhat of a two stage process, there is room for more error, especially in low light.
  • Pentax's autofocus has long been a topic of discussion here.
  • Pentax's flash system does also lag behind Canon and Nikon. That will probably add to the problem.
  • Rumor has it that the K5 firmware updates did address some concerns, so you might want to upgrade to the latest version.
The K5 is much improved over the past bodies. The K5 also has the focus light that does help quite a bit, however it does depend on what you are taking pictures of.....

Last edited by interested_observer; 05-19-2012 at 05:57 PM.
05-19-2012, 05:53 PM   #4
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Check out this posting from the K-r section.

Also, while the K-r's auto-focus adjustment is generic to all attached lenses, I seem to recall from another post that you can store the auto-focus fine-tuning for multiple lenses on the K5.

05-19-2012, 07:25 PM   #5
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I never had any other brand DSLR but Pentax kx and k5
so I really do not know how good canon and nikon focus in really dim light situation.
but my experience is kind similar to you. in very low light situation, many of my photo come out like yours. but in good lighting situation. it is fine. so I think it is not something regarding front/back focus issue.
but really, sometimes the place is just too dark, like in bar, club, I can hardly see the person face. I am not blaming my k5 that much if it can not focus accurately.
can canon and nikon really do that well?
05-19-2012, 10:31 PM   #6
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Af is Pentax's Achilles heel. Low light AF inaccuracy in tungsten light is a known issue with the K5, and compared to Nikon, the AF is probably 3 generations behind.
05-19-2012, 11:08 PM   #7
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The Nikons do.

QuoteOriginally posted by liukaitc Quote
I never had any other brand DSLR but Pentax kx and k5
so I really do not know how good canon and nikon focus in really dim light situation.
but my experience is kind similar to you. in very low light situation, many of my photo come out like yours. but in good lighting situation. it is fine. so I think it is not something regarding front/back focus issue.
but really, sometimes the place is just too dark, like in bar, club, I can hardly see the person face. I am not blaming my k5 that much if it can not focus accurately.
can canon and nikon really do that well?
Don't know about Canons, but my Nikons do. I have lots of pictures of indoor parties of people dancing where it is almost absolutely dark. I cannot see the people's faces. But the pictures come of nice and sharp.
05-20-2012, 12:11 AM   #8
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Sigh. Not another AF discussion. And as is customary, everyone is jumping straight to conclusions, based on a series of casual snapshots, and presumptions about Pentax vs Canon vs Nikon etc.

K-5 AF is rated EV-1 to EV 18 at ISO 100, so those scenes of OP are well within the illumination range for Pentax AF to work properly. (Especially when flash is involved, which it is in these sample images. So we aren't really talking about low-light AF here anyhow...)

QuoteOriginally posted by sanjeevdas Quote
Sometimes I will change the focus point to where I want the focus to be. In most of these I pointed at the face and recomposed.
If Pentax had face detection in it's phase-matching AF (via the view finder, rather than via liveview, where there is the option of face-detect) that might work. Otherwise the AF points of any camera are not laser targetting dots, but just regions of differential contrast in the area indicated by the focus points.

I also note that in all of the sample images where you report problems, flash is involved, and low shutter speeds too. Use of flash means what you are reporting is not really a low-light AF issue at all, but a flash settings + technique + AF issue.

I suggest that you test any purely AF accuracy speculations by doing your tests properly against static subjects.

At a minimum for any tests:
- choose a flat subject/ test target with *one* strong area of vertical or horizontal contrast right in the centre,
- set AF to centre-spot,
- set ISO to 100
- set AF to AFS
- set lens aperture wide open
- set the target at a medium distance (ie more than 2 m),
- put camera on a tripod,
- turn off SR,
- take any UV or other filters off the lens
- provide good even illumination of test target for initial tests, then vary light strength and as required light temperature (eg tungsten, LED, daylight, flash, whatever) if that's what you want to test.

Then draw some conclusions.

05-20-2012, 12:59 AM   #9
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I would as well that you should check the AF accuracy and eventually tune it. You know you can do this, right?
05-20-2012, 08:29 AM   #10
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I know it is not the subject but why not use manual focus? I always do as long as I can do a better job than the AF, which I can in most cases. I have never been dissapointed!
05-20-2012, 10:26 AM   #11
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QuoteOriginally posted by rawr Quote
Sigh. Not another AF discussion. And as is customary, everyone is jumping straight to conclusions, based on a series of casual snapshots, and presumptions about Pentax vs Canon vs Nikon etc.

K-5 AF is rated EV-1 to EV 18 at ISO 100, so those scenes of OP are well within the illumination range for Pentax AF to work properly. (Especially when flash is involved, which it is in these sample images. So we aren't really talking about low-light AF here anyhow...)

I also note that in all of the sample images where you report problems, flash is involved, and low shutter speeds too. Use of flash means what you are reporting is not really a low-light AF issue at all, but a flash settings + technique + AF issue.

.
I agree a more controlled test in desirable. However, I don't understand the point you make above. Even if flash is used, the camera does not use the flash when it is _trying_ to lock focus. The flash is only used when I actually press the shutter fully. While the camera was trying to lock focus, it was pretty dark. The flash exposure helps me evaluate the image _afterwards_ to check for focus accuracy because it prevents camera shake and motion blur typical of these situations. The low shutter in these cases (where I am using flash) in inconsequential because the flash the flash exposure time is much lower than the shutter speed anyway. Am I missing anything?
05-20-2012, 10:29 AM   #12
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QuoteOriginally posted by Pål Jensen Quote
I know it is not the subject but why not use manual focus? I always do as long as I can do a better job than the AF, which I can in most cases. I have never been dissapointed!
You probably do a much better job at manual focussing than I do. I haven't done much manual focussing, but I agree it is a good skill to learn.
05-20-2012, 10:30 AM   #13
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QuoteOriginally posted by Zav Quote
I would as well that you should check the AF accuracy and eventually tune it. You know you can do this, right?
Yes, I can tune it. However, the AF is dead on in good light from what I can tell. I will do some more controlled tests in the next few days, though.
05-20-2012, 10:36 AM   #14
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QuoteOriginally posted by hcc Quote
Thank you for the comprative comments. I fully agree your comments about the superb primes offered by Pentax: eg, the FA Lrd series, DA Ltd series, some FA* vintage lenses (FA*85mm), and many more. Your comment on weight is interesting. We take for granted that Pentax cameras have SR and the lenses are lghter.

In very low light, MF lenses are definitely a must IMHO. I shoot outdoor at dawn and dusk and my favourite lens is the VL58mm f1.4. It is MF and works great.

Another option with AF lenses is to pre-focus manually. It works nicely with lenses equipped with Quick-shift, but it works also with other (eg FA) lenses.

I add that I do not have experience with Nikon or Canon in low lights. I only speak from my experience with K-7 and K-01.

Hope that the suggestion may be of interest..
Thanks for the suggestions. Yes, Nikon does not have any small primes like the DA15 and DA21. I like wide more than tele. The K5 is also smaller (both in height and width) than the D7000 (although similar weight). The combination of the K5 and the small primes almost makes it like an advanced P&S with an OVF and the the DSLR advantages.
I will try the pre-focus approach. Thanks for the suggestion.
05-20-2012, 10:45 AM   #15
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QuoteOriginally posted by sanjeevdas Quote
Even if flash is used, the camera does not use the flash when it is _trying_ to lock focus.
Depends on the camera and the flash. My K-r uses a low-power LED in low-light to assist auto-focus. My Sigma EF-610DG Super flash has its own LED that performs an identical function when attached to the camera.

I will note however that the camera typically doesn't automatically go to its X-sync shutter speed of 1/180 second. It will often pick a much slower shutter speed to capture background detail unless I intervene. So, unless I either intervene or use a tripod, what might appear to be an out of focus subject is in fact a blurred subject due to camera movement.
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