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01-27-2008, 02:14 PM   #1
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AF, the K10D and tungsten lights

So I recently stumbled across the most glaring issue of all with Pentax: the 100% tendency of backfocusing under tungsten light when using AF. I read the thread that told how to adjust AF with firmware 1.10, but as I don't know if a firmware downgrade is possible, and I can't find the firmware anyway, so this doesn't seem relevant. I have read that the K20D allows AF adjustment, but I do not have $1200 to spend on only a body (just got this one for $900 with a 50 1.4), will not pay the 10% restocking to return this current camera, and am definitely happy with it despite the AF issues. Now, I'm seriously considering that my switch back to Pentax is a major mistake. I had no idea this issue even existed, or that it could exist. In lieu of all this, I have discovered I have 3 options:

1. Send the camera back, lose $100 on it and switch back to the canon 400D/450D (please god no!)

2. Send the camera back, and save up for a $1200 body. As a student with no job, this will take the better part of a year, not to mention cancelling all the weddings, portraits, assignments etc I have set up for this year. Basically, not an option.

3. Get a Katz Eye split focusing screen, and use manual focus. Bresson did it, shouldn't I be able to as well?
Pentax K10D Focusing Screen - Katz Eye Optics

As you can see, the prospects are bleak. I'm using money I did not intend on using in absolutely every circumstance (beside keeping my camera the same, which is simply stated, not an option).
I'm sorry that this is basically a rant, maybe I should have simply asked whether the Katz Eye screens are actually worthwhile, but I had to take out my anger somewhere.
Thanks for any and all input!

01-27-2008, 02:46 PM   #2
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I would suggest testing the camera yourself to see if this is a problem for you. That way you know the limitations of your camera in the circumstances where you will be using it. Perhaps you won't have a problem.

Another idea is to get a Pentax flash that allows for the focussing assist beam.
01-27-2008, 03:03 PM   #3
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QuoteOriginally posted by hudsong Quote
So I recently stumbled across the most glaring issue of all with Pentax: the 100% tendency of backfocusing under tungsten light when using AF. I read the thread that told how to adjust AF with firmware 1.10, but as I don't know if a firmware downgrade is possible, and I can't find the firmware anyway, so this doesn't seem relevant.
Then you didn't look hard enough....
RiceHigh's Pentax Blog: How to Get Back to an Older Version of the Firmware?
firmware 1.10 for k10d. : Pentax SLR Talk Forum: Digital Photography Review
I am under the impression that YOU found this to be the case, not just what you heard....
The AF module is sensitive to IR (as confirmed by people using the vis light blocking filters on a lens) AND IR actually has a different area of focus sooo in low light (tungsten) w/ a high proportion of ir (which I believe may apply under these conditions) there could be some focus issues... but I'm still not sure this is really the case. This issue may apply to ALL brands (except those that are IR blind AF modules)
Just food for thought.

Last edited by jeffkrol; 01-27-2008 at 03:15 PM.
01-27-2008, 03:10 PM   #4
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Have you personally experienced "100% back focus under tungstan light" with your K10D? I have tested mine carefully, with my FA 50/1.4, FA 100/3.5, and DA 18~55 and not found consistant back focus with any of the lenses under tungstan or daylight. The 50/1.4 is a bit tricky under low light conditions of any sort, since the DOF at f/1.4 is VERY shallow, but I have not seen consistant preference for back or front focus. There are issues with manual focus using fast lenses due to the microlens design of the focusing screen; the Katz Eye split image screen is supposed to pretty much take care of that issue... most people who go with a Katz eye screen seem pretty happy with it; I plan to buy one the next time the budget allows (I have a number of legacy MF lenses that I like to use).

Of course, if your K10D does exhibit 100% Back Focus (and there certainly are some out there, from this forum), your best option is to send it to Pentax for service. Sounds like they are giving pretty quick turn around for those who avail themselves of warrenty service...

Curt

01-27-2008, 03:31 PM   #5
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I don't have the K10D but the DS which has the same AF system. I am aware of RH's claim that Pentax DSLRs BF in tungsten environment. I have tried to reproduce this claim a few times carefully but failed. My personal conclusion is that the choice of light does not actually affect the accuracy, but the EV level does. Since most tungsten lights are really dim compared to daylight, perhaps this gave the wrong impression that it was the light source that caused BF. But I can say that w/o sufficent light or contrast, the AF will be less certain and sometimes less accurate. There are also many factors that can impact the AF accuracy. For instance, AF sensor & focus screen alignment, AF calibration, subject size and contrast, background contrast, focal length etc. Sometimes the ever-so-slighty AF miscalibration of the body might confuse the users. And man do I hate those "angled" tests which I think is doing more harm than good. If you want to calibrate the AF, use a virtual infinity target with a 43 or 50mm prime (could be a building far away etc). Many people trying to calibrate focus with a close-up target will only be disappointed with confusing results.
01-27-2008, 05:03 PM   #6
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Original Poster
Hey guys,
I don't know about RH's reputation around here (I'm new, as you can see) but I find he seems strangely anti pentax for having a bunch of pentax cams and using them for years. I think I jumped to conclusions here: I did some more rigorous testing with focus charts in natural light, and I've discovered that my lens backfocuses consistently no matter what the type of light is. I put on a lens my dad owns, and I had ZERO issues in both natural and tungsten lighting. I also used some high efficiency lights for another test, and some normal shots of things in general for a control, and found while my Dad's lens was nice and sharp, mine was backfocused 9/10 times. Thanks for your quick replies, and I guess I need a new lens, not a new camera.
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