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PostPosted: Sun Jun 15, 2008 4:19 am 
My apologies if it was discussed before, and I simply missed it (I just started reading Camera Labs).

There are places which show examples of hot pixels issue in K20D (various K20D bodies), and describe them it in some details (Google if you are curious). Pentax eventually confirmed the problem and will release a new firmware to address the issue - most likely not by really fixing (I do not believe that it is fixable), but by improving algorithm of dynamically masking the hot pixels with interpolated values.

There are many interesting points here, and one needs to understand that most cameras are also affected by similar problem, but each handles it a bit differently: some reasonably well, other so-so. Good cooling of the sensor is the best solution, but not practical in consumer equipment beyond a small, passive insufficient heatsink. As the sensors become more and more stressed beyond what they can cleanly deliver I observe (sometimes with amusement) what manufacturers do in firmware to compensate. None of the manufacturers documents what they did in firmware beyond a few words, so back engineering or testing the results is the only way to find more about it.

I am just curious why comprehensive K20D Camera Labs test does not mention it at all? Did I miss something, did the tester(s) were unaware of the issue and the fact that Pentax confirmed it? A few other tests I read here are very good, thus such omission almost looks to me like I missed something.


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PostPosted: Sun Jun 15, 2008 10:32 pm 
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Simple: I didn't mention them because there weren't any in my test shots!


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PostPosted: Sun Jun 15, 2008 11:14 pm 
I understand, you were not sufficiently curious to investigate further why others have seen this problem (and posted tests showing it), and why Pentax is working on a fix for something you did not find in your tests.


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PostPosted: Mon Jun 16, 2008 4:01 am 
darius, I believe hot pixels rarely show up during normal usage. However they may appear after extensive use of live view as said by reviewers of other website.


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PostPosted: Tue Jun 17, 2008 12:58 pm 
byte, my understanding is that hot pixels are simply noise manifestation of digital imaging sensor (also named 'dark noise', or 'image noise'). More of them appear when the sensor overheats, thus prolonged use of live view is one scenario which could trigger more of them to appear, very long exposures (night shots) is another. See for example this from Hasselblad:

"Image noise in the Hasselblad H3D-II has been significantly reduced by improving the cooling of the sensor, achieved by attaching to the CCD a physical heatsink, which dissipates the heat generated to the entire camera body and considerably lowers the temperature of the system"

I found it strange that a reputable site can test the same camera, and does not even mention the issue which was already widely known and discussed elsewhere, also acknowledged by Pentax. Not seeing something which many other people saw is significant, and should lead to: "why I am not seeing this?" or "how is my test different?" or "are there different K20D bodies being sold?" etc, etc.

BTW, I do not believe that Pentax fix addressed the issue, but as at this stage I can not re-test myself, I am not in a position to contribute anything more.

byte wrote:
darius, I believe hot pixels rarely show up during normal usage. However they may appear after extensive use of live view as said by reviewers of other website.


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PostPosted: Tue Jun 17, 2008 2:24 pm 
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Hi darius,

I'm sure potential purchasers of the K20D will be interested in the issue you have flagged. There is a good write-up about this in the PDF document Short analysis of K20D hot pixel phenomenon. The conclusions presented in this document are as follows:
    • There is no significant difference in hot pixels between Pentax *istDS and K20D.

    • Hot pixels shouldn't be a problem for normal exposure times.
    • Otherwise, the hot pixels are real and w/o dark frame subtraction, there too many of them. Most of them are dim, though.
      Dark frame subtraction seems to stop doing its job for exposures of 1000s and longer. Still works for 150s at ISO400, though.
    • Hot pixels tend to form clusters and such clusters, most likely, escape the RAW converter removal.
    • In rare, non reproducible cases, a 2s exposure can contain 10000s of dim and 1000s of visible hot pixels (Pentax K20D only).
    So, all in all, these seem to be normal properties for a DSLR CMOS/CCD sensor.

    The only finding left as a concern for the K20D is a single, non reproducible image from the K20D with excess hot pixel noise.
By the way, I suspect that a couple of typos have crept into the quoted text but the overall meaning is clear, especially in light of the penultimate paragraph.

In light of this report it is certainly not surprising that Gordon didn't see the problem. Indeed, from the above it might even be suspected that the seriousness of the problem has been over-stated and your own worries about the camera and Gordon's methodology have fallen prey to that process.

Anyway, I forget my manners and as this is my first reply to one of your posts may I wish you my usual warm welcome tot the CameraLabs forums. Are you already a DSLR owner or are you contemplating becoming one? Is (or was) the K20D on your shortlist?

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Wed Jun 18, 2008 8:05 am 
for some reason my entry was duplicated, so I am editing out one of the duplicates.


Last edited by darius on Wed Jun 18, 2008 8:06 am, edited 1 time in total.

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PostPosted: Wed Jun 18, 2008 8:05 am 
Hi Bob,

Thank you for your response, and the pointer to the hot pixels PDF doc, this is first informative quality material I have seen which really explains the issue. falconeye should be congratulated.

And thank you for your welcome message, I appreciate that. I am a professional engineer with around 40 years of industrial experience in high precision mechanical and electronics industry. I did own many cameras in my life, at the moment I have access to and I am using various equipment, so I do not have urgent need to buy any, but I will probably get a camera soon anyway. Overall I am very disappointed with current development in this field. By the way, I believe that I am very experienced engineer, but also totally average photographer.

Over the last 40 years or so I observed tremendous progress in my field, but not in the consumer digital photography which in my view created almost nothing conceptually new. All I see are hybrid designs, very similar between different brands, where electronics is simply added to old SLR mechanical design and practically no new ideas are developed. I may as well go to a shop and say: "just give me a dSLR for around $1,000 please, I don't care which brand". And I know that I will get one of very similar products with similar, cloned design. I know very well how a camera is designed as a piece of machinery, and I understand well how it operates; for me Canon - Nikon - Pentax - Olympus, etc, all just follow the same path and the same old concepts. Within the same price bracket I see no difference between the designs.

Sorry for this long-ish rant, and most likely unpopular view. As usually: yes, this is my personal view only, anyone is free to disagree. Yes, K20D is on my short list, but I still have faint hope that maybe we will see something really different in September... though I doubt it.

BTW, I found Camera Labs tests to be excellent and enjoyable to read, one more reason to be surprised that the hot pixels issue so many noticed was not even mentioned in the test.

cheers, Darius


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PostPosted: Wed Jun 18, 2008 9:40 am 
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Hi Darius,

I'm glad you found that document of interest. I tend to agree that most DSLRs are, to paraphrase, "good enough". That said, most of us find that how a camera feels "in hand" is surprisingly important and can be quite different not just between manufacturers but between different models in a particular manufacturer's range. So, as you get closer to making your choice please do get down to a store and take as much time as you need to handle the goods.

As for thinking out of the box, look at the lukewarm response to my thread Why is the lens at the front?. :lol:

Bob.

_________________
Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Wed Jun 18, 2008 11:29 am 
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Hi Darius, the absence of any mention of it in my review has nothing to do with lack of curiosity.

First, the issue was being widely reported after my review was published.

Secondly, there were no hot pixels present on any of my test shots, many of which were taken with the two second self timer.

So if there's nothing to observe on the images and there's no issues being reported at the time of writing, that would explain the lack of comment in the review.

Gordon


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PostPosted: Wed Jun 18, 2008 12:52 pm 
Gordon,

The issue was widely reported well over a month before 18th May when your review was published.

Some examples:

If you search dpreview Pentax forum you will find hundreds of post and sample photos from many K20D bodies discussing the hot pixels issue well before 18th May.

dpreview announced on 8th May freezing pending K20D review until Pentax comments on the issue.

Polish Web site optyczne.pl published samples of hot pixel photos and finding from many K20D bodies on 12 April.

...and the list goes on and on...

cheers, Darius


Gordon Laing wrote:
Hi Darius, the absence of any mention of it in my review has nothing to do with lack of curiosity.

First, the issue was being widely reported after my review was published.

Secondly, there were no hot pixels present on any of my test shots, many of which were taken with the two second self timer.

So if there's nothing to observe on the images and there's no issues being reported at the time of writing, that would explain the lack of comment in the review.

Gordon


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PostPosted: Wed Jun 18, 2008 1:11 pm 
Hi Bob,

Funny you should mention it... for me Nikon Coolpix swivel body series was promising new direction, similar to what you described in your post. I kept my 4500 as an example of innovative thinking, and proof that new technology opens new horizons. Sadly the concept was abandoned by Nikon. Have a look here:
http://www.dcresource.com/reviews/nikon ... 00-review/
and here:
http://www.coinopgamemuseum.com/sample/coolpix.html

cheers, Darius

Bob Andersson wrote:
Hi Darius,

I'm glad you found that document of interest. I tend to agree that most DSLRs are, to paraphrase, "good enough". That said, most of us find that how a camera feels "in hand" is surprisingly important and can be quite different not just between manufacturers but between different models in a particular manufacturer's range. So, as you get closer to making your choice please do get down to a store and take as much time as you need to handle the goods.

As for thinking out of the box, look at the lukewarm response to my thread Why is the lens at the front?. :lol:

Bob.


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PostPosted: Wed Jun 18, 2008 3:47 pm 
Off-topic:

Those were the Nikons I was referring to! Nikon did release a subsequent line of follow-up models actually but I haven't seen a new one for about two years now.


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PostPosted: Wed Jun 18, 2008 8:28 pm 
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Darius, I don't tend to frequent a website which takes an agressive stance against cameralabs. Would you visit somewhere you weren't welcome? And I haven't seen that Polish site.

Besides I prefer to conduct my own tests and come to my own conclusions rather than trawling rival forums for problems.

Anyway, you know my reasons for not mentioning the problem. It didn't affect my sample and I wasn't aware of any issue while I was writing the review.


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PostPosted: Fri Jun 20, 2008 1:51 am 
Gordon Laing wrote:
Besides I prefer to conduct my own tests and come to my own conclusions rather than trawling rival forums for problems.


i'm sure i'm not the only one who appreciates the integrity and effort you put into doing your reviews gordon.

i was not able to replicate the hot pixel issue either, but i still went ahead and did the firmware update.


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