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09-06-2011, 05:02 PM   #1
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Would K-5 have better AF for my lenses?

The lenses in question are the FA 50 f/1.4 and the DA 12-24 f/4. I have the K20D and must say that I've been more than frustrated on several occasions by the AF performance in low light. I realize this is a frequent complaint with the K20D, but these lenses are my worst offenders; my DA 10-17 Fisheye and DA 35mm Macro Limited are much better in terms of AF, but they also struggle in lower light situations, and I often use MF only with the FA 50 and DA 12-24. Obviously, I would prefer to be able to trust my AF much more.

So to those of you who own these lenses and a K-5 and have upgraded from the K20D, would the upgrade to the K-5 be worth it in terms of AF accuracy?

09-06-2011, 05:18 PM   #2
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I say yes but my opinion doesn't matter. I've yet really to run into a situation where I cannot focus. The built in AF assist lamp does help some. I'll note that in completely dark situations, all of my AF lenses tend to struggle.

What exactly You mean by struggle though, I don't know.

09-06-2011, 05:19 PM   #3
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The K-5 is more accurate regardless of the lens, so yes. It's still not on par with Canikons AF system (IMO), but it's much better than its predecessors. You'll rarely see it hunt.

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09-06-2011, 05:24 PM   #4
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The K5 seems to struggle less than the K20 does in low light, but the K5 can also give false AF lock.
I've found that with both cameras, when the light levels go down, manual focus is the name of the day, which is unfortunate, since this is exactly when AF is desirable.
The K5 AF beam helps a lot, but it also has all the subtlety of a fart in an elevator.
Overall, the K5 AF is improved greatly over the K20, but it is not perfect.
As an aside, I have or have owned all the lenses you mentioned. I sold my FA50/1.4 in favour of the DA*55/1.4.

09-06-2011, 06:07 PM   #5
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QuoteOriginally posted by Wheatfield Quote
I've found that with both cameras, when the light levels go down, manual focus is the name of the day, which is unfortunate, since this is exactly when AF is desirable.

Overall, the K5 AF is improved greatly over the K20, but it is not perfect.
Manual focus with the DA 12-24 is a pain, because the subject is often so small in the viewfinder especially when I'm zoomed out.

As for the AF not being perfect, I'm sure no camera has perfect AF. However, I'm thinking the K-5 would seem that way to me in comparison to the frustration the K20D has produced.
09-06-2011, 07:10 PM   #6
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After using the K5 for several months, I have become used to the much better AF , so I sort of take it for granted. But...every morning and evening when I mount my Bigma 50-500 and go Squirrel hunting, I am reminded of the striking difference between the K20D and the K5 in AF.

On the K20D the Bigma would hunt like a half blind hound in anything but the best of light. Even then,it could be slow enough that I could get in a few sips of coffee before it locked. The K5/Bigma locks sure and fast, well, as fast as a big lens like the Bigma can move...which is not like the speed of light! The only time it hunts now is in very dim light. Mostly it will lock then if there is nothing else in the scene causing focus interference.....little limbs and leaves are always a problem for a Big Game Squirrel hunter!

So....after a long winded lesson on Squirrel shooting, the answer is yes, the K5 is honestly and no kidding much faster to AF and this has related to all my lenses, not just the Bigma.

Best Regards!
09-06-2011, 07:10 PM   #7
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QuoteOriginally posted by enoxatnep Quote
Manual focus with the DA 12-24 is a pain, because the subject is often so small in the viewfinder especially when I'm zoomed out.
This is what annoys me about how the APS-C sensor cameras have integrated their viewfinders. When the istD came out, I compared it's viewfinder image size to that of my LX, and found they were identical, given an identical lens to view through.
So what, one would say, it makes perfect sense.
And it does, except that when your standard focal length is 20mm shorter, you are looking at your standard lens as if it's a wide angle, and somewhat of a wide as if it's a super wide, etc.
Unfortunately, this is what we are stuck with, physics being what it is and all, but I'd take a somewhat dimmer finder to get something sized more like a 35mm film viewfinder.
With any luck, EVFs will become viable at some point, but right now they are execrable, so the optical viewfinder, compromised as it is, is still our best option

QuoteQuote:
As for the AF not being perfect, I'm sure no camera has perfect AF. However, I'm thinking the K-5 would seem that way to me in comparison to the frustration the K20D has produced.
What I noticed with the K20 was that the AF would stop and start, it would lose lock after finding a target, and in one particularly annoying instance, the focus locked, the confirmation light was on, and the dratted thing sat there with it's dunce cap on and caused me to miss one of the more important moments at a wedding I was shooting.
The K5 has been much nicer to me than the K20 was in this regard. It also has a much better sensor if you like shooting at higher ISOs. What I find I'm doing with the K5 is bumping the ISO much higher than I was able to do with the K20 and using the extra speed to allow me to stop down a bit more, thereby hiding any focus inaccuracy.
09-12-2011, 10:47 PM   #8
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QuoteOriginally posted by enoxatnep Quote
Manual focus with the DA 12-24 is a pain, because the subject is often so small in the viewfinder especially when I'm zoomed out.
I use my Sigma 10-20/3.5 only in manual focus mode (because my K100D cannot drive the HSM motor). However, I practically never have an issue with focus. The DOF is so deep with most aperture settings that the hyperfocal distance is pretty near.

I think ultra-wides are difficult to focus for any camera and manual focusing will most of the time be more than sufficient and even outperform AF sometimes.

As for the K-5's low light AF capabilities, have you looked at the 'LumoLabs: Pentax K-5 low light focus study is published' thread? When the K-5 was introduced, many people noticed AF issues in low light and sometimes (depending on how fast lenses were), "low light" meant studio modelling light levels.

Back then some people (e.g., Smeggypants, IIRC) claimed that their K20D performed better in low light than their K-5. After Pentax released a firmware update addressing the AF issue, many people were happier with their K-5's AF performance but falconeye's re-test attested no significant improvements. Whatever Pentax may have fixed, it had no relevance in his test conditions.

The K-5, even with an up-to-date firmware, does not meet its "-1 EV" AF limit specification and with slower lenses the EV level at which the AF becomes inaccurate can be as high as EV 4 or more, IIRC.

It is clear that the AF module (i.e., the optical path and the respective sensor) of the K-5 is very capable and the most sensitive of any Pentax DSLR yet. However, it is let down by a not quite so sensitive metering system which is on double duty for metering and reporting colour temperature for AF adjustments to counteract focus shifts, e.g., in Tungsten light. When the light meter goes blind in low light, the AF module compensation stops working and there is a sudden drop in focus accuracy. It appears that there is still a bug lurking in the AF code because the focus error shouldn't be that discontinuous, but Pentax never followed up with another firmware update.

This may not be a complete bummer, but as Wheatfield said, the K-5 will happily report AF lock despite the focus being significantly off target in very low light situations. In other words, a K-5 AF lock is not something you can rely on in such situations.

What's the upshot of all this? In good light, the K-5's AF is significantly better than the K20D. In not so good light, the difference might be even larger. In really, really low-light, the K20D might have an advantage since it doesn't suffer from the K-5's AF bug (see falconeye's article). Whether the K20D can really outperform the K-5 in low light, I don't know. There were some reports along these lines by users, but to the best of my knowledge no reliable test has ever been performed.

I reckon you'll perceive the K-5's AF as a significant improvement that you'll find worthwhile even if -- and that's a big IF -- there might be extremely low light situations where the K-5's AF performance will be worse than that of the K20D.

You should be fine with the 50/1.4 because it will provide a lot of light to the metering chip, i.e., the AF will cop out much later than with a slower lens. The 12-24/4 isn't that fast which means you'll potentially see AF inaccuracies in light levels 8 times brighter (3 stops) than with the 50/1.4. But then, again, I don't think AF is that important for the 12-24.

I hope this helps.


Last edited by Class A; 09-12-2011 at 11:04 PM.
09-13-2011, 04:55 AM   #9
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"When the light meter goes blind in low light, the AF module compensation stops working and there is a sudden drop in focus accuracy. It appears that there is still a bug lurking in the AF code because the focus error shouldn't be that discontinuous, but Pentax never followed up with another firmware update."

This is a huge bummer for me. I've been borrowing my brother's K110D and I consider it the "quick dirty magic camera." The focus was never a problem, however I upgraded to the K-5 since with the K110d there was so much noise at a higher ISO. But I still have well-focused images from that camera, though grainy. Most (if not all) of my photography is low light/natural light. I specifically bought the k-5 for its expanded high ISO range but noticed right from day one that I had to work significantly harder to get a well-focused image in normal daylight household conditions. Not even dreadful conditions. But midday sun and I'd have to bump the ISO to 3200 to compensate for unfocused shots at ISOs 800-1600. Luckily the K-5 images still look superb at that high of an ISO but still...

Now I'm tempted to return the camera before my 30 days is over. I've already messed with different focus points and maxxed out my shake reduction, etc. But what's the point of a high ISO performer when exactly when you need it you can't rely on the auto focus?

So if I return it, any advice for a Pentax that's a "step down", maybe better high ISO performer than the K110d but without the focusing problems of the K-5? Any help would be great. Thanks
09-15-2011, 05:35 PM   #10
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Thanks for your input, everyone. I'll admit that when I first checked one out last winter I was excited by the fast AF and the great high ISO capabilities. However, reading about an AF system that isn't much better than my K20D doesn't get me too excited. I've even been browsing lately at *gasp* Canikon systems, wondering if their AF reliability is better. I know their AF speed is better, and their noise at high ISO's is well-controlled like the K-5, but I'm growing tired of hit-and-miss when I need to rely on AF.
09-15-2011, 05:46 PM   #11
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AF might be more reliable in low light with the Canikons but I've had good success with the K-5 ensuring I point the focus point to the right spot (the highest contrast spot on the subject).
09-15-2011, 10:17 PM   #12
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QuoteOriginally posted by enoxatnep Quote
However, reading about an AF system that isn't much better than my K20D doesn't get me too excited.
The K-5's AF system, according to everything I've read about it, is much better than that of the K20D.

Only in low-light, it has a remaining issue, but note that
  1. it is not entirely clear whether the K20D does better (the K20D does not even attempt to make a correction for light temperature and will front-focus in warm light temperature situations for sure)
  2. it is not clear to what extent models from other manufactures have similar problems. Christine Tham reported that her K-5 did much better than another camera she had (I think it was a Canon). I think that report is completely unreliable, but you may still want to consider it.
Falconeye performs very thorough experiments and has thus uncovered the K-7 shutter blur issue and the K-5 low light AF issue.

Who knows what issues would be uncovered with Canikon models, if the user base had a Falconeye amongst them?

Undoubtedly, the K-5's AF system has room for improvement in low-light but it is not so clear cut to what extent the same also applies to many models from other manufactures.

Last edited by Class A; 09-15-2011 at 11:42 PM.
09-24-2011, 10:33 PM   #13
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I had a chance last night to try my "problem" lenses out (that I mentioned in my original post) on a friend's K-5 and I must say that I was impressed! I was focusing on objects after sunset with very little ambient lighting and even if focus wasn't always quick (I don't recall ever having a fast AF system from any other camera in such conditions), it was accurate. It made my K20D an embarrassment in comparison. I don't think I'll be spending too much time any more checking out what Canikon has to offer. Just thought I'd give this update, plus thank all of you for your input on this matter.
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