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02-23-2011, 06:39 AM   #46
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QuoteOriginally posted by audiobomber Quote
I agree with Quicksand. I tested my K20D and K100DS and found they FF in tungsten light and focussed properly in daylight, no matter if it was dim or bright. I didn't bother to test my K-x when I got it, but I know it does the same thing.
But isn't that the "normal" light color dependency?

Probably w/o a big jump.

What I found is that the light intensity where the focus jump takes place is light color dependent. But the jump itself is rather consistent and large. I assume K-x and Co. have a defocus which smoothly depends on the deviation of the light color from daylight (to be investigated).

And then there's the magnitude of jump: 200m at f/2.8 are 10 pixels blur! Are other cameras really similiar?

Any K-5 AF photographer really has to care to stay above the focus jump threshold.

02-23-2011, 06:44 AM   #47
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Falconeye,

You note in your paper that AF integration time varies from < 1ms to 250ms. Did you observe a non-linearity of AF integration time with respect to EV? Either a step function with decreasing EV as in the defocus data, or a "ceiling" that is reached even while EV goes lower? Again the data tease with possible 0xFF effects.
02-23-2011, 06:50 AM   #48
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Thanks for your work, Falk !
02-23-2011, 07:08 AM   #49
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QuoteOriginally posted by Michaelina2 Quote
Instead, assuming the OP is working independently and not a troll in sheep's clothing, it might be more appropriate for each reader who feels the report means something to contribute some money so he can keep his "Errors and Omissions" insurance policy current. I'm NOT a lawyer, but it seems reasonable, if Hoya can find an error in the OP's methodology and can show that error produced damages (thank you all who have publicly declared they will not buy due to the OP's study results), he could be held liable for multiples of the damages. BTW: Does anyone wonder why someone would want to insert themselves into a public discussion in such a conclusive way using an N=1? Based on other experiences, surely the OP is aware of the time and energy black-hole he's creating for himself, plus the self-inflicted headaches to follow? Again, just curious... M
PentaxImaging of the US advertises the K-5 as a"Professional" camera and if you care to look at the specifications for the K-5, you might ask yourself who is being duped or harmed. Compared to how certain previous generations of Pentax cameras performed, it is quite reasonable to expect the K-5 to meet its specifications. What is the point of buying something, where the superlative advantages of the product are crippled by either design, manufacturing, assembly, hardware or software issue.
Add to that the various other issues that have received widespread attention, it is only prudent for "informed" consumers to wait instead of going thru the hassles that others have experienced so far. Some consumers won't wait, buying into another system they perceive as more reliable and functional.

This forum and others, and forum members like "Falconeye" provide exactly the kind of information that gives us a chance to make a somewhat educated decision when buying specific camera products. I am the one parting with my money, expecting a product that works as advertised.

Once again, products fail and have faults, but when these faults are systemic of the product line, then it may be time to put on the brakes. There really is no fine line between "Marketing" and reality. Meet your stated specifications or lose me as a customer.

02-23-2011, 07:11 AM   #50
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QuoteOriginally posted by the swede Quote
If Pentax had put a brand new SAFOX in there, they would be more than happy to announce that, even before the lauch of the K-5. They do it with everything new they come up with, so they would have done it.

only my very humble opinion though
Well good old Pentax was (is?) very marketing sleepy.
They never advertised the fact that their AF lenses (all of them) report focus distance to the body. Nikon bit the drum awfully when they introduced AF-D lenses.
This is just an example.

Hoya may be different though.

I have no proof of what I say. I'd wouldn't be surprised AT ALL though.It'd be VERY VERY Pentax-like.
02-23-2011, 07:12 AM   #51
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I had sent the letter to Pentax support about AF assist lamp algorithms of K-7 and I got an answer - that no any issues with work of AF lamp.
I also asked about AF assist lamp settings in menu in new cameras. Nothing.

Things are still where they started...Alas...
02-23-2011, 07:34 AM   #52
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QuoteOriginally posted by falconeye Quote
But isn't that the "normal" light color dependency?

Probably w/o a big jump.
Yes, I realize the K-5 behavious is different. I was responding to the assertion by some that earlier Pentax cameras did not exhibit low-light focus issues. The behaviour I described, FF under tungsten light, is not just a Pentax issue.
02-23-2011, 07:56 AM   #53
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AF integration time chart

QuoteOriginally posted by cfraz Quote
You note in your paper that AF integration time varies from < 1ms to 250ms. Did you observe a non-linearity of AF integration time with respect to EV? Either a step function with decreasing EV as in the defocus data, or a "ceiling" that is reached even while EV goes lower? Again the data tease with possible 0xFF effects.
I've done a chart for you. Defocus vs. AF integration time.

AF integration time becomes 250ms if the lightvalue becomes about 0EV or less. But even at higher lightvalues it can become 250ms. Overall, it doesn't look as if the problem would be correlated with the 250ms AF integration time state.

Nevertheless, if AF integration time is 250ms then the probability for a focus jump seems to be large too, about 50%.

Also note that AF integration time and LV is only loosely coupled. Sometimes, the AF module would "underexpose" (i.e., take too little time to do its measurement) and then an accuracy at low light appears for a short AF integration time.

Attached Images
 

Last edited by falconeye; 02-23-2011 at 08:07 AM.
02-23-2011, 08:31 AM   #54
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QuoteOriginally posted by Catalana Quote
PentaxImaging of the US advertises the K-5 as a"Professional" camera and if you care to look at the specifications for the K-5, you might ask yourself who is being duped or harmed. Compared to how certain previous generations of Pentax cameras performed, it is quite reasonable to expect the K-5 to meet its specifications. What is the point of buying something, where the superlative advantages of the product are crippled by either design, manufacturing, assembly, hardware or software issue.
Add to that the various other issues that have received widespread attention, it is only prudent for "informed" consumers to wait instead of going thru the hassles that others have experienced so far. Some consumers won't wait, buying into another system they perceive as more reliable and functional.

This forum and others, and forum members like "Falconeye" provide exactly the kind of information that gives us a chance to make a somewhat educated decision when buying specific camera products. I am the one parting with my money, expecting a product that works as advertised.

Once again, products fail and have faults, but when these faults are systemic of the product line, then it may be time to put on the brakes. There really is no fine line between "Marketing" and reality. Meet your stated specifications or lose me as a customer.
Regardless of market impact, reverse engineering and posting for peer (other users, mostly technically inclined) review is a protected form of free speech in many progressive jurisdictions. Same for basic evaluative testing on a continuum towards greater technicality. Otherwise DPR and DxO would not be in biz, nor Car & Driver magazine, etc. As long as there is diligence in the data and methodology, always with the potential for retraction, then sales impact is moot. This is how markets for products work when products are accompanied by technical information (detailed spec sheets in advertising) beyond trade puffery.

Non-issue.
02-23-2011, 08:51 AM   #55
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Thanks!

1.) According to Pentax, the 645D also uses the SAFOX IX+ autofocus system. From your findings and knowledge, dare you speculate about any implications?
K-5 - 645D

2.) From the "Defocus vs. AF integration time" chart one could suggest to skip/redo/... all focussing with integration time > 100ms . Perhaps color coding the EV might bring some more insight .

3.) I hope that the software solution will not be the simple addition of a (second) corrected (e.g. by fixed 250m) picture.
02-23-2011, 09:21 AM   #56
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Dear Falk,

Fantastic job you did again. Hope that all consumers around the globe will profit from it.
02-23-2011, 09:55 AM   #57
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QuoteOriginally posted by falconeye Quote
I've done a chart for you. Defocus vs. AF integration time.

Thanks! So it looks like increasing max AF integration time wouldn't help the nasty FF step function, maybe just reduce scatter a bit.
02-23-2011, 11:06 AM   #58
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QuoteOriginally posted by falconeye Quote

Maybe, the AF assist light behaviour (single or multiple engagements) is lens dependent rather than camera dependent. Could be another important clue.
I get all sorts of AF assist light behavior just by randomly pointing at different targets in a fairly dark room. Sometimes one short blink followed by one quick movement, next time (at another target) one long beam while gradually turning the lens a few times, or three short blinks with three short adjustments.

What strategy to use seems to be dependent on target and light available.
02-23-2011, 11:17 AM   #59
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QuoteOriginally posted by falconeye Quote

Fig.1: Accuracy of the Pentax K-5 phase detect AF vs. luminosity in EV. The above chart includes all measurements, i.e. various lenses, light colors, distances and apertures. The accuracy is measured as deviation of the focal plane from the sensor plane, in m. [from the study linked below]

LumoLabs (that's me ) has decided to have a closer look at the K-5 low light front focus issue. After careful evaluation and many hundred test shots I must say that the issue is real.


Please, keep discussion within this thread related to the above study and work which is based on experiments. We have another thread for the exchange of observations and opinions.
It is here: https://www.pentaxforums.com/forums/pentax-k-5-forum/128562-relevant-news-re-...ial-light.html

Thanks everybody for their motivation. I probably wouldn't have done it without. Again it turned out to be more work than anticipated
The above mentioned Thread seems to be stopped. Will the discussion be somewhere else?

Earl
02-23-2011, 11:40 AM   #60
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QuoteOriginally posted by falconeye Quote
But isn't that the "normal" light color dependency?

Probably w/o a big jump.

What I found is that the light intensity where the focus jump takes place is light color dependent. But the jump itself is rather consistent and large. I assume K-x and Co. have a defocus which smoothly depends on the deviation of the light color from daylight (to be investigated).
Yes, exactly right. On my K20D, the amount of defocus seems to vary, predictably, depending on the quality of the light. If I go straight from outdoor daylight into tungsten incandescent light (even in a well-lit room), a -10 focus compensation will just about fix it. For lighting conditions between those two (fluorescent, twilight, etc.) the amount of compensation required will vary.

Fortunately, it only matters a lot when using wide-aperture lenses, and it's possible to predict and manually compensate for the problem in most cases, at least on the K20D because it allows custom focus tuning. Many cameras seem to have this problem, and many people gripe about it, but somehow people still seem to get some excellent pictures!

I wouldn't consider this a bug, in the older cameras. Just a known design limitation.

This K-5 phenomenon is, no doubt, a bug. Falk's scatter plot shows that peculiar clustered distribution that strongly, in my opinion, indicates some defective processing or programming.

I think I'm considerably more optimistic about the likelihood of a fix, though -- I'd consider it much higher than 50%.
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