See these two reports and threads. They are 100% self-explanatory, with direct quotes from those Pentax officials:-
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=39947770
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=39975810
Btw, for what I have tested scientifically, that "specific spectrum of light" is called Infra Red. Red light does NOT cause any FF problem to the AF of the K-r, neither does the Green light, which *implies* Yellow light should NOT cause any problem neither! But since tungsten light sources do come with also strong IR spectra. So, it should be the real cause. I have also checked that adding a stronger Skylight 1B filter, which moderately suppresses both Green and Blue lights as well as IR, could lessen the FF very slightly. Thus, the dominant IR in environment should be the root cause to the problem as it is verified and re-confirmed.
After all, it seems that the AF sensors of the K-r are just too sensitive to IR but yet the IR cutting filter used in the AF module is either non-existent or is not strong enough and thus causing this problem - which could never be cured via firmware as it is a *hardware* issue, as I predicted on day one! (but then fanboys rebutted with NO ground and jumped on me, as usual!)
In fact, I confirmed this tungsten AF FF issue at the beginning of this year shortly after I purchased my K-r. I, as many other K-r users who have been suffering from the problem, of course was/were much disappointed for this step back of the SAFOX IX, especially for those who "upgraded" from a previous Pentax DSLR like the K-x and K-7, which do not have this severe issue.
Frankly, Pentax should have created a SAFOX IX-(minus) system instead of what is called the SAFOX+, adding what so-called an additional yellow-light detector won't help them and we end-users, BUT SIMPLY adding an IR cutting filter would! >:-(
Last but not least and still, here is my (repeated) advice for an interim measure to the problem: 1. Turn off the "AF Assist" light in the custom function and then 2. Set "AF Fine Adjust" to -10 (maximum value, my K-r usually focuses somehow acceptably at 0 under daylight for most of my Pentax lenses) and DO *remember* 3. Disable "AF Fine Adjust" after you return to non-tungsten environment and BEFORE you shoot! Easy Enough? :-o
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Saturday, December 03, 2011
Pentax UK and Pentax Germany Admitted K-r Tungsten Front Focusing Issue (But there is No Solution, as Both Clearly Told)
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Comments by IntenseDebate
Pentax UK and Pentax Germany Admitted K-r Tungsten Front Focusing Issue (But there is No Solution, as Both Clearly Told)
2011-12-03T01:14:00+08:00
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Focusing Accuracy|Issues|K-5|K-7|K-r|K-x|My Reviews|News|Pentax|Technical Articles|
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flomat · 694 weeks ago
Barry F · 694 weeks ago
I will continue to pursue Pentax on this until a satisfactory outcome is found for K-r users.
The worst point is that this model is still on sale..thus an exchange won't help users.
Barry F · 694 weeks ago
Barry F · 694 weeks ago
If needed it's possible to pursue other avenues on this too: http://www.tradingstandards.gov.uk/advice/index.c...
Is one such option I have explored this of yet..but I will if they don't deal with it effectively.
Note the point about: fit for purpose and of satisfactory quality.
Barry F · 694 weeks ago
I also posted off a fairly no nonsense letter to Pentax Japan HQ explaining the problem in detail that will take a while to arrive but it's worth a shot.
I know some users have just given up any hope of this getting looked at, but I'm not known for letting something like this slip such a serious problem cannot be overlooked. I would encourage users to contact Pentax and complain and try to "increase the volume on this"
Obviously Pentax must be aware the more this is discussed and talked about on forums and the internet..untold damage is being done to potential buyers who might look at what would otherwise be a damn fine camera for the money. I hope I don't have to but I am quite happy to dedicate some serious time to ramping up the internet campaign on this..there are many forums..lots of keywords which will make the message very loud, and extremely clear. Let's hope Pentax try to get this one looked at.
Barry F · 693 weeks ago
The K-r is a cracking camera it's a real let down it has this issue
Barry F · 693 weeks ago
Pentax service now informs me that they are working on a firmware fix for this problem. He did not know when it would be available to download but assured me it was being undertaken as a priority.
I just wanted to pass that one on..let's hope they can sort this problem out
Barry F · 693 weeks ago
In light of the fact Pentax has not contacted me directly (as of yet)
I've left a fairly damning review on the DPR user review pages in the hope potential K-r buyers are fully aware of this.
Should this situation change I will update the review to reflect that.
I really hope they were not leading me on and that there is a firmware update..but I can't accept the poor service I have had from the company so far. If they wanted to sell a dodgy DSLR to a customer, they've picked the wrong one in myself.
Putting it mildly I'm furious with Pentax and I'm about to unleash hell on the net warning other potential buyers