K5 tungsten vs daylight AF calibration?? GordonBGood, awaldram, RPulley?

Started Nov 11, 2012 | Questions thread
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Brian Thomas Contributing Member • Posts: 562
K5 tungsten vs daylight AF calibration?? GordonBGood, awaldram, RPulley?

I'm trying to calibrate a new k5 before a big trip to India and I'm no engineer. I photograph a lot under low light. Basically, I first ordered when they were announced a K5iis and got an incorrectly assembled model (only me!). I saw that the K5 had plunged in price and some people here had gotten it to focus correctly so I thought I'd take a chance with it.

(By the way, k5 users, did you notice that the k5 has one cool feature that was removed from the k5II series? -- Image comparison, a great display mode that lets you compare any 2 images on your card side by side magnify sections of each. This is great for those long  train or bus rides.)

I have upgraded the k5 firmware. I was using the chart at 45 degree angle as recommended by GordonBGood and downloadable from here: http://photo.net/learn/focustest/

but had a hard time discerning the result with that. I may return to it. I'm now using moire live view method versus phase detect method described here:


Gordon states that he has gotten his low light tungsten AF within a few millimeters of his low light daylight focus.

.."firmware at versions 1.13 have a very slight shift to front focus between daylight and tungsten illumination of about three mm. at f/2.8 and minimum focus distances of about 40 cm. This is little enough that one can bias the micro focus adjustment just enough to the rear that both daylight focus and tungsten focus are within the Depth Of Field (DOF) for f/2.8, with the daylight DOF slightly biased toward the back and the tungsten DOF slightly biased toward the front."

I am doing this test at the photo.net article recommended 25 times the focal length or, for the DA 40 about 39 inches.

I have some maddeningly specific questions, especially for GordonBGood & awaldram & RPulley,

1. Can you quantify the low levels of light, the ev level, that I should be able to get to work with a sample iso, f-stop & shutter speed?

2. Can you quantify the micro bias adjustment between tungsten & daylight in Pentax micro adjustment numbers, rather than millimeters? i.e. The Pentax k5 adjustment goes between -10 to +10. My first tests show the tungsten test at quite bright levels of light calibrated at "0" and the low light daylight test at "-7" How far a distance can be safely split as Gordon recommends?

3. If a lens that you have been successfully using with kx requires a bias of -10 or +10 to be close to right, would you send the camera back and get the k5II series?

I have been doing the moire test AF on my laptop and then putting the laptop to sleep and then focusing on my dark tungsten lit dirty laptop screen. Amazingly it locks focus. Nonetheless, it is extremely front focused. The final question is..

4. If I slip a piece of paper on top of the screen to make the tungsten light focus easier, is the width of that sheet of paper so insignificant that the test is still valid?  (f2.8 at 25x the focal length)

Thanks for reading this. I realize that this is asking a lot, but I have included links to the test methods involved so that this post might be a new reference point for future users.

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