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10-04-2016, 03:44 AM   #1
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information needed, K-70 autofocus performance compared to K-S2

Hello.
I'm proud (not really) owner of K-S2. I'm a little bit disappointed (in fact, i'm very disappointed) with its AF performance. It is lacking both speed and accuracy with every lens i have, which are: native 18-135, Tamron 70-200, Sigma 17-50/2.8 and DA-50/1.8
Is the AF performance of K-70 better then K-S2?

10-04-2016, 04:11 AM   #2
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Hello and welcome to the forums

It's well known that Pentax AF isn't quite so accomplished as some of the competition, but it's still very good. If you're getting AF speed and accuracy problems with every lens, that doesn't sound like a general K-S2 problem to me. Can I ask, how are you assessing AF accuracy and speed? Which AF modes and focus points are you using in which situations? Have you set up a focus test scene or tool, and checked for front/back-focusing, then made individual AF fine adjustments for each of your lenses?

Of the lenses you own, I have two - the Sigma 17-50/2.8 and the DA50/1.8. The Sigma is an excellent lens, but I don't find it 100% reliable on AF compared to most of my Pentax lenses. It's good, but not quite as consistent as - for example - my DA Limited lenses. The DA50 should focus well in good light, but I find it can be a little hit and miss in lower light situations. The Tamron 70-200 is an excellent lens if calibrated properly, however I've had two of them that front-focused badly and were outside the +/-10 AF fine adjustment limits (I ended up returning both lenses). I still own a Tamron 28-75/2.8 that also front focused quite badly, and I sent that to Tamron's UK distributor for service and alignment. It now works perfectly, requiring -4 AF fine adjustment.

Let us know a little more about the situations where AF isn't working well for you, and we may be able to help you get better results.
10-04-2016, 05:26 AM   #3
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I can describe the AF performance of my K-S2 as inconsistent. I am using single point AF, focusing for mid point for portraits, and select single point (other then central one) for report shooting. Yes, the problem is mostly present in dim light. And the results is the same for every of my lenses.
For instance, i shoot a backstage for local fashion show, and like 30% of my shots went to bin because of missed focus. Not that images were very blurry, but just slightly out of focus. Other 30% were so-so, and other 30% were acceptable. The rest were good.
High Fashion Show 2016 backstage | Flickr thats that album, theres only photos which i consider as acceptable quality, just for demonstration of the shooting conditions.
I can not notice front or backfocus, because, as i mentioned, some shots is just fine, and some are slightly missed in both directions.
But my question was about K-70, not my current problems, because i dont believe i'm that bad.
10-04-2016, 05:48 AM   #4
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QuoteOriginally posted by GraySaint Quote
I can describe the AF performance of my K-S2 as inconsistent. I am using single point AF, focusing for mid point for portraits, and select single point (other then central one) for report shooting. Yes, the problem is mostly present in dim light. And the results is the same for every of my lenses.
For instance, i shoot a backstage for local fashion show, and like 30% of my shots went to bin because of missed focus. Not that images were very blurry, but just slightly out of focus. Other 30% were so-so, and other 30% were acceptable. The rest were good.
High Fashion Show 2016 backstage | Flickr thats that album, theres only photos which i consider as acceptable quality, just for demonstration of the shooting conditions.
I can not notice front or backfocus, because, as i mentioned, some shots is just fine, and some are slightly missed in both directions.
But my question was about K-70, not my current problems, because i dont believe i'm that bad.
The reason I was interested in your current problems is that there is a risk you could experience the same on any current Pentax camera if the issue is to do with lens calibration and/or technique (not to suggest there's anything bad about your technique - but none of us here knows how experienced you are with Pentax cameras specifically). If you're only getting 10% of shots that are perfectly focused, and another 30% that are acceptable, that is well below reasonable expectations with modern Pentax cameras such as the K-S2. Something, somewhere, isn't right.

I'll leave you to discuss the K-70 with other members, but I strongly recommend that - whichever camera you use - you calibrate your lenses using AF Fine Adjustment, and ensure you are using the most appropriate AF modes and focus points in the most efficient and reliable way for the subjects you're shooting. There's no reason why you shouldn't be getting 80% or more keeper shots.

10-04-2016, 06:18 AM - 1 Like   #5
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As a first step, I would check back/front focus. Although you don't think there's a problem there, it's quick and easy to check. Maybe you need to apply a slight adjustment to the camera body. The calibration can be just slighlty off enough to cause problem with many shots, but not bad enough to still be able to get some pictures right.

Were you using AF.C or AF.S ? Also note that older than SAFOX XI aren't particularly good at keeping focus at subjects moving toward you. Were you bad shots corresponding to this situation ? But, even then, you should get better than 10% good shots, unless they're moving fast at relatively close distance...

I don't have the KS-2 but a camera with the older SAFOX IX+. I get a much higher hit rate than you, but all my lenses are calibrated and some required signifiant microfocus adjustements (particularly the zooms) to get consistently good shots. I can't even tell you the proportion since misfocused shots are few enough that I don't care about them. Your KS-2 should do better than my older camera.
10-04-2016, 06:38 AM   #6
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Thank you for ansvers and interest for my problem. Maybe i am not making myself clear, but my question is not "i am not happy with my AF performance, how to fix it", it is "is the AF performance of K-70 better then it is on K-S2"
I mean, i am aware that Pentax cameras have AF problems, especially with moving subjects. It is ok, i managed to work around it.
For instance, i am taking a picture of urbanscape from tall building, and focusing on the sky, assuming that focus will be on infinity. Sometimes it does. Or, i am focusing on a contrast object, and again, sometimes the focus is right. Most of the times. The tuffer the light conditions goes, more inconsistent becomes AF performance. I can understand that.
But does K-70 AF performes better than K-S2 does (in not ideal conditions)?
10-04-2016, 06:49 AM   #7
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No, the K-70 AF won't perform any better than the K-S2 for stills photography. Both of them use the SAFOX X AF module. The K-3 and K-3II use the SAFOX 11 engine, which does provide better auto-focus performance, but other factors such as lens calibration and correct technique will influence whether you get any better success rate with those cameras (or any other camera, for that matter).

Focusing on the sky (clouds? clear blue sky?) is inherently unreliable, and in any case will not give you the correct focus for an urbanscape. I won't go further into this here, as I realise you only want to know about the K-70.
10-04-2016, 06:51 AM   #8
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The AF performance will be about the same. The K-70 & K-S2 get their AF from the older K-5II/K-5IIs. You'll need a K-3 at the minimum for better AF. The K-3II has slightly better AF. Hopefully the upcoming next generation APS-C flagship will have even better AF.

10-04-2016, 06:52 AM   #9
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I don't think using the 70 200 wide pen at 2.8 is going to help your focusing problems whatever camera you use.
10-04-2016, 06:56 AM   #10
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QuoteOriginally posted by GraySaint Quote
But does K-70 AF performes better than K-S2 does (in not ideal conditions)?
Both have the same AF system (SAFOX X). So, no, the K-70 shouldn't be significantly differently different than the KS-2 in terms of AF performance. To get better performance, you'll have to move up to a K-3 or K-3ii. Both having a much improved AF system (SAFOX XI).
10-04-2016, 07:35 AM   #11
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Thank you for your ansvers.
Yes, i undersand that operator can help AF by focusing on contrast objects, avoiding dim lighting, and using greater apperture numbers then wide open. But sometimes you just can not do that, and have to rely on your gear.
10-04-2016, 07:44 AM   #12
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I'll close with three final comments, given your last reply...

You may rely on your gear, but your camera (Pentax or any other) relies on having a suitable target for AF. If a suitable target isn't available, an alternative to "hoping for the best" (which often results in disappointment) is to focus manually. AF systems are clever, but they need something to work with. If that something isn't available, we photographers have to step in and do the work for them

For the urbanscapes you mention, you want to be shooting stopped down quite a bit, and focusing on part of the scene that is roughly one-third into the region you want to be acceptably sharp - focusing on the sky (if it even works at all) will result in a significant portion of the scene closer to you being out of focus. Apologies if you're already familiar with this, but I thought it worth mentioning.

For the fashion shoot, I notice from a couple of shots I looked at that they were taken with the Tamron 70-200 at f/2.8. Please do note what I said previously about the two copies of the 70-200 I owned - both front-focused badly, and this would be most noticeable at f/2.8 where the depth of field is shallow. You have some really nice lenses, so whether you continue to shoot with the K-S2, buy a K-70, or upgrade to a K-3 or K-3II, take the time to carry out controlled AF testing and AF fine adjustment on them.

Last edited by BigMackCam; 10-04-2016 at 07:50 AM.
10-04-2016, 08:35 AM   #13
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I've tested all my lenses for focus accuracy, and they all do well, but i did so in good lighting, at almost perfect conditions. Maybe i should test them in dim lighting, not for calibration, but as the test, and see, what results will be. As i mentioned, i've got inconsistent results in hard conditions, so maybe such experiment will teach me how to work around that.
10-04-2016, 09:52 AM   #14
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I own a K-70 as an upgrade from a prior K-50. In terms of AF, there are only a few select areas of improvement in focus, otherwise as explained above it's pretty close to the K-50 and so likely to the K-S2.

- Liveview AF has improved, not sure if it's the SAFOX X or if it's the "much overhyped" Hybrid AF. I find that I'm using it a lot more than I ever had previously. CDAF isn't the only function working as it's not hunting like Liveview did with the K-50.
- Pentax FAQ does show Liveview has the Hybrid AF (Type Hybrid AF *1 = TTL Phase-matching AF + Contrast-detecting AF)
- AF-C is possible in video now with my 18-135 DC lens (there's a longer list of lenses PENTAX K-70 | FAQ | Support | RICOH IMAGING.
List as of now, I recommend checking the FAQ periodically as new lenses are released.
*1 Compatible lens
 smc PENTAX-DA 18-135mmF3.5-5.6ED AL[IF] DC WR
  HD PENTAX-DA 55-300mmF4.5-6.3ED PLM WR RE
  HD PENTAX-DA 16-85mmF3.5-5.6ED DC WR
  smc PENTAX-DA L 18-50mm F4-5.6 DC WR RE
  HD PENTAX-DA 18-50mmF4-5.6 DC WR RE
  HD PENTAX-DA 20-40mmF2.8-4ED Limited DC WR
  HD PENTAX-D FA 28-105mmF3.5-5.6ED DC WR
  HD PENTAX-D FA* 70-200mmF2.8ED DC AW
  HD PENTAX-D FA 150-450mmF4.5-5.6ED DC AW
  HD PENTAX-DA 560mmF5.6ED AW

- AF-C and Electronic AE works in video with my 55-300mm PLM lens.

Use of the AF with the Viewfinder appears to be identical, which is PDAF with 11 points, nine of which are cross-type. Lame.. as this seems to be 10 year old AF tech.

There are a number of significant upgrades in terms of ISO limits with very low noise due to the "accelerator" chip that goes with the Prime MII (same exact CPU as your K-S2 and the prior K-S1, the accelerator is the only new function). More pixels resolution and the Pixel Shift feature. But that really is only significant over the older K-30 and K-50 cameras. If you have a K-S2, either wait another generation or as recommended by the other posters go for a K3 II. I'd do that over a K3 as the KAF4 mount is supported on the K3 II with a firmware upgrade. Regardless if the hardware can support it or not, Pentax doesn't appear to have any intention to add it to the K3 regardless of survey attempts to call it to their attention.

Last edited by SeaRefractor; 10-04-2016 at 09:55 AM. Reason: For clarity
10-04-2016, 10:19 AM   #15
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QuoteOriginally posted by GraySaint Quote
For instance, i am taking a picture of urbanscape from tall building, and focusing on the sky, assuming that focus will be on infinity.
I think you have a problem with your technique, GraySaint.

You cannot focus on a sky, with PDAF of any camera you focus on a line, and only on the cross AF points can the line be either horizontal or vertical.

Alarm bells went off when you said you aimed at the centre of models in dim light. How do you know a line can clearly be seen (allowing its two halves to be aligned by the focus module) instead of the AF point falling on a patch of dress material?



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