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01-18-2012, 11:48 PM   #1
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Battery level affecting K-5 autofocus?

Hi all,

I have begun to suspect that the ability of my K-5 to autofocus quickly and accurately in low light is affected by the declining battery charge -- before the battery is unable to power the camera and before the battery meter on the top LCD shows any sign of depletion.

I think I've also had this behavior previously shooting with a K-7 and, before that, K20D, though I never thought to test it out.

Anyone else observed this?

I use both Pentax and aftermarket batteries, but most recently noticed the issue with a Pentax brand.

Unless I'm shooting on assignment or heading out for a full day's shooting on my own somewhere, I tend to let the batteries run all the way down, as it's easy enough to replace them here at home. That means that some part of the time, my cameras are running on near-empty, as it were, even though they don't give any clear sign of that condition.

This evening I was messing around shooting some low-light handheld shots in the livingroom, and was frustrated with my inability to get crisp shots with the 16-50/2.8. The camera would seem to lock focus, but the image was seriously out of focus or blurred. Perhaps 50 shots later, I noticed the battery meter was showing a drop in charge (whatever the first increment of depletion is). I swapped to a fresh battery and the focus was perfect. (* Another possibility, come to think of it, is a low-battery SR failure. Or both.)

In similar incidents I recall with the K-7 and K20D, the focus wouldn't lock at all in dim light, just before the meter said to replace the battery. New battery >> improved AF.

Makes me wonder whether some people's varied experience with Pentax AF, especially in low light, could result from low battery charge that is not being indicated on the meter. It could be a subtle wildcard affecting performance.

Perhaps the next time I run a battery down -- I already put tonight's on the charger, so it's too late now -- I'll run a test.

I'd love to hear of anyone else's experience/theories.

01-18-2012, 11:52 PM   #2
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It might be worth it to do a controlled test of this to confirm.

It would make sense that a lower battery voltage could slow down the AF drive, but it shouldn't prevent the AF sensor from making an accurate reading.

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01-19-2012, 12:30 AM   #3
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I haven't observed it, but I haven't looked specifically for it either. And it doesn't make much sense either as the voltage from the battery most probably is regulated to a certain value. And (again most probably) the camera will shut down before the batteries own voltage falls below the regulated value.
01-19-2012, 12:50 AM   #4
Brooke Meyer
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Shooting events, all of sudden no focus, intermittent, see battery indicator, pop in a new one, all fine. Yep, need a fresh battery. Low or high voltage will cause all sort of strange things, especially in micro-electronics.

Since last summer, I always let my K-5 batteries wear down because the K-5 chargers will keep charging a fully charged battery for a long time, overcharging it. That causes the "any" button fires to fire the thing and/ or extra mirror flops. With my K-20's, I used to check the battery by popping it in the charger before a shoot . The K10/20 charger would momentarily light up charging and then go out on a fully charged battery.

You put a battery in the K-5 charger, let it fully charge and the charger light goes out when it senses full voltage. All ok. Forget which one, put back in, the charger doesn't sense full and starts a new charge cycle for a long time. I had to quit topping off batteries (as I did with my K-10 & 20's) in July. Had a lot of back to back shoots so daily top offs really showed the issue. It is repeatable, not intermittent. I only use Pentax batteries.

I have not had an issue on either K-5 with the "any" button or double flops since July when I quit topping off charges which isn't an issue as I always have extra batteries. I've put at least 10 to 15K exposures since on each body with no further problems. With 40 years of experience in electronics & IT, it made perfect sense. It would not take much in the way of over voltage to cause what Lockheed Missile engineers taught me as "well known, random system phenomena".

But when I let them run down, as I seldom used to, you'll find out in a hurry with no focus et al

01-19-2012, 05:32 AM   #5
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It sounds like a plausible conjecture. One way this *could* work would be the AF motor taking its power from an unregulated supply rail, directly from the battery (*). With this current through the coil decreases with decreasing charge (voltage), hence torque decreases and hence the speed at which the motor can move the focus mechanism. Further, to optimize for AF speed, the firmware might estimate the amount of physical movement due to inertia after power to the AF motor coil is cut, and, crucially, get this wrong with a depleted battery.

(*) which would make sense to use the charge more effectively (that is not convert some of it to heat in the regulator), also, the regulator would not need as much cooling (a heat sink), could be a lower spec part and would probably do a better job keeping the voltage stable for the electronics

Last edited by jolepp; 01-19-2012 at 08:21 AM. Reason: typo
01-19-2012, 06:14 AM   #6
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On thing to keep in mind is that these batteries do not handle full discharge / charge cycles that well, as this shortens their life expectancy...

Brooke, your experience with the charger is strange, as I clearly recall mine doing the checkup cycle just as expected with a fully charged battery (the led briefly lights up then goes out).
01-19-2012, 08:28 AM   #7
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Hmmm, I wonder if the grip would change anything?
Controlled testing sounds like a very good idea.
Anyone considered it yet?
01-19-2012, 09:19 AM   #8
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Not meaning to hijack this thread, but how should the K-5 battery be stored?
I find the instructions on page 4 of the manual to be rather ambiguous.

• Storing the battery fully charged may decrease the battery performance.

Avoid storing in high temperatures.

• If the battery is left inserted and the camera is not used for a long time, the

battery will over-discharge and shorten the battery’s usage life.


01-19-2012, 10:23 AM   #9
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good fine, i have never thought about this.
it sure is worth to experiment it.
01-19-2012, 10:47 AM   #10
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Same issue here. I have both OEM and after market and once they run down a bit, unless I use live view, the focus is off randomly due to various factors (strong backlight, strong light at an angle, not much contrast, etc)
01-19-2012, 10:58 AM   #11
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QuoteOriginally posted by bkpix Quote

snipped...

This evening I was messing around shooting some low-light handheld shots in the livingroom, and was frustrated with my inability to get crisp shots with the 16-50/2.8. The camera would seem to lock focus, but the image was seriously out of focus or blurred. Perhaps 50 shots later, I noticed the battery meter was showing a drop in charge (whatever the first increment of depletion is). I swapped to a fresh battery and the focus was perfect. (* Another possibility, come to think of it, is a low-battery SR failure. Or both.)
I have had similar experience a few times in the past with my 16-50/2.8 focusing in error even when it had a lock focus (focus indicator shown from photoME on the person's face but the focus was actually in the background); and I noticed that soon after that happened, the battery indicator showed low/depleted level and then I had to change battery in the camera to continue.
01-19-2012, 09:59 PM   #12
Brooke Meyer
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QuoteOriginally posted by OK5 Quote
Not meaning to hijack this thread, but how should the K-5 battery be stored?
I find the instructions on page 4 of the manual to be rather ambiguous.

• Storing the battery fully charged may decrease the battery performance.

Avoid storing in high temperatures.

• If the battery is left inserted and the camera is not used for a long time, the

battery will over-discharge and shorten the battery’s usage life.
I keep 2 charged batteries in the pockets of a vest. When a camera battery depletes while shooting, I swap it. Since I shoot often, I don't know about leaving them in the camera, there is always a battery in the camera, including the K20 on the shelf as a backup. There have been no problems in the last 4 years.
01-19-2012, 10:19 PM   #13
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It does indeed seem like there may be two issue here worth further controlled testing:

- Battery overcharging by the charger
- Poor voltage regulation circuitry in the camera

If there is good voltage regulation in the camera, an overcharged battery should not be a problem. Likewise, a nearly depleted battery should also work until it drops below nominal operating voltage for the camera, at which point it should shut itself off.

I try never to put a freshly charged battery directly into the camera right off the charger. This is when the battery voltage will be highest, and this will slowly drop over time to nominal battery voltage. If someone who has had focusing problems linked to apparent low battery charge and/or mirror flops which seem to be related to high voltage overcharging, then a simple test could be made using 2 Pentax batteries. Never put the freshly charged battery in the camera, but keep the spare charged ready to go, and swap the battery when the first one gets low. Then charge the fist battery and keep it ready for when the 2nd goes down. Always give the battery at least 24 hours resting period before putting it in the camera, to let the supposed overcharge dissipate.

I'd run this test myself, but I have only one battery at the moment.

Last edited by cbope; 01-20-2012 at 02:37 AM.
01-20-2012, 02:31 AM   #14
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QuoteOriginally posted by cbope Quote
Battery overcharging by the charger
Quite hard to believe. I'm sure everyone can recognize a dead, puffed battery, not to mention a battery on fire. Because those happen when a Li-Ion battery is overcharged.

QuoteQuote:
Overcharging Lithium-ion

Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage. Prolonged charging above 4.30V forms plating of metallic lithium on the anode, while the cathode material becomes an oxidizing agent, loses stability and produces carbon dioxide (CO2). The cell pressure rises, and if charging is allowed to continue the current interrupt device (CID) responsible for cell safety disconnects the current at 1,380kPa (200psi).

Should the pressure rise further, a safety membrane bursts open at 3,450kPa (500psi) and the cell might eventually vent with flame. The thermal runaway moves lower when the battery is fully charged; for Li-cobalt this threshold is between 130–150CC (266–302F), nickel-manganese-cobalt (NMC) is 170–180C (338–356F), and manganese is 250C (482F). Li-phosphate enjoys similar and better temperature stabilities than manganese.

Last edited by simico; 01-20-2012 at 02:39 AM.
01-20-2012, 02:43 AM   #15
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It's not black and white as you describe. Li-Ions can be slightly overcharged without damage, as long as they are not overcharged too far. Several posters have claimed that a fully charged pack placed on the Pentax K-5 charger goes through a full charge cycle instead of just a simple topping off or trickle charge cycle. This suggests that overcharging is very likely.

It's the same with laptop batteries. In fact, my new Lenovo has a battery-life saving feature that it will not engage the charging circuit unless the battery is below 95% charge. This prevents overcharging a fully charged battery.
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