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10-08-2008, 03:28 PM   #16
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QuoteOriginally posted by deejjjaaaa Quote
sorry to disappoint you.
stay classy.

The color of lighting has no effect on focus. If it's not the focusing distance it's the intensity. Make sure your pure tungsten light is the same intensity as pure daylight.

For a 60 watt bulb, that would be about a foot away from your test target. Probably even closer.

Should be easy enough to measure with a light meter if you have one.

But I'm telling you, my camera has no such phenomenon.

10-08-2008, 05:19 PM   #17
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konraDarnok, The test shots i took were in the exact same lighting, just different lenses... my two DA lenses focused properly, the FA50 however has about an inch of back focus (maybe a little less)
10-08-2008, 05:25 PM   #18
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QuoteOriginally posted by konraDarnok Quote
But I'm telling you, my camera has no such phenomenon.
I do trust you - my position is that any BF/FF is a body & lens combination issue... my setup has it, yours doesn't - lucky you...
10-08-2008, 05:33 PM   #19
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QuoteOriginally posted by konraDarnok Quote

The color of lighting has no effect on focus. If it's not the focusing distance it's the intensity. Make sure your pure tungsten light is the same intensity as pure daylight.
what else should I ensure ? may be that my pure tungsten has the same spectrum as my pure daylight... I am not Bruce Almighty, can't put a sun inside my dining room @ 12 AM...

10-09-2008, 04:53 AM   #20
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If the k20D's +/-10 fine tune settings cannot correct the BF/FF problems, what else can we do? Any other solutions other than to send them to pentax?
10-09-2008, 05:34 AM   #21
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QuoteOriginally posted by mitchkramez Quote
konraDarnok, The test shots i took were in the exact same lighting, just different lenses... my two DA lenses focused properly, the FA50 however has about an inch of back focus (maybe a little less)

If you feel comfortable with it, The 1.01 debug menu isn't difficult to use. Give it a try. (but of course, it's your camera, and your risk if you mess something up)

Use the maximum 1.4 aperture on the lens. Adjust the focus + a step at a time until you get consistently focused shots. Use a test chart and then move on to real world subjects.

From my own perspective the learning curve was kind of steep. Focus errors are just a fact of life -- I just kinda got a feel for when the result was reliable and when it was a random error. I spent a few days taking shots and reviewing them. I took hundreds of photos and explored the extremes of what that focus adjustment would do.

For my camera + 60um was the correct setting. It makes the FA 50 and other large aperture lenses I have (being various m42 lenses) tack sharp on what you're pointing it at. As for the slower zooms, you won't notice any change -- they just have a larger Depth of Field that masks the back focus.

Although, for me, I was getting back focus problems at the wide angle end with my 18-55mm. Those were also remedied when I adjusted the camera.

Good luck. Hopefully this is of some kind of help.
10-09-2008, 06:04 AM   #22
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QuoteOriginally posted by deejjjaaaa Quote
what else should I ensure ? may be that my pure tungsten has the same spectrum as my pure daylight... I am not Bruce Almighty, can't put a sun inside my dining room @ 12 AM...
It is my contention that the camera will exhibit random focus errors in low light. If the camera is already back focusing, it's just going to exacerbate the problem.

Full direct sunlight outputs 60w per square meter. That's a lot of light. If your dining room has a 60w bulb, I'm going to guess you'd need to put whatever you're using as a test target for focusing about 1 foot from that light bulb in order to ensure that you're getting the same intensity of light as you do with your day light shots.

If you had a light meter, you could make sure it was the same intensity.

The purpose is to make sure your focus error is related to the color of the light, rather than the intensity of the light -- by removing the focus errors that low light levels will induce.

If you're still seeing a discrepancy in focus under those conditions, I'd be inclined to believe that the camera exhibits focus errors because of different light sources.

I'm simply dubious of that -- as I've nearly convinced myself of that -- but in the end, I found there were plenty of other reasons that could be attributed to focus error that was unrelated to whatever device was emitting the photons. Be it a CFL, a tungsten bulb, or the sun.

imho.
10-09-2008, 07:04 AM   #23
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QuoteOriginally posted by konraDarnok Quote
It is my contention that the camera will exhibit random focus errors in low light.
sorry, but the target is a very well lit regular DOF testing target... good enough to go ISO100 @ 1/100s... do not mix focus hunting in a dim light (whether is it a dim daylight or dim artificial light) with BF/FF (which is consistent and corrected by AF adjustments).

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