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10-06-2021, 08:44 AM   #1
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Artifact on photos from K7

Hi -

I took some photos at an event a couple of weeks ago and found that some of them have a thin green vertical line starting in the upper left part of the photo. I'm including two of those - K7b-0596 and K7b-0599. I also found an image with a purplish vertical line I'm including it also - K7b-0601. I'm using a K7 for the photos.


The artifacts weren't visible on all the photos -- I'm hoping that means they weren't on all of them. Does anyone have any thoughts about what the artifacts are and if there's anything to be done about them?

Thanks,
Gil

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10-06-2021, 08:57 AM   #2
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Hi

Seeing the photos at web size I can not see what you are seeing.
10-06-2021, 09:12 AM   #3
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I don't see it either with these shots. Likely you have a bad column on the sensor or a hot pixel that is causing the column to go bad.
We'd need a RAW image, not compressed to be able to tell what is going on.
Try covering the lens (completely black) and shooting a long exposure (30s) to see if it really shows up.
10-06-2021, 09:24 AM   #4
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Ok, I'll try that. When I've done it, if I want to share the raw image, will uploading it to my cloud account and sending a link work?

10-06-2021, 09:46 AM   #5
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Green and purple lines seems to be in same position, it means that 2 vertical lines of pixels are effected. What is the reason? I don't know, but this type of failure can indicate problems inside the sensor's circuitry. Maybe pixels in the line are always active like hot pixels? I suggest to make Pixel mapping procedure if it is available on K7, maybe this will help.
10-06-2021, 11:04 AM   #6
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QuoteOriginally posted by tallytvguy Quote
Ok, I'll try that. When I've done it, if I want to share the raw image, will uploading it to my cloud account and sending a link work?
Yes it will
10-06-2021, 05:19 PM   #7
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I uploaded the photos above to the cloud -- jpeg and raw versions. I also took the :30 black frame exposure suggested by ProfessorBuzz and uploaded .jpg and raw versions of it -- k7b_0947. The link is below.

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Thanks again.

10-06-2021, 06:50 PM   #8
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I see the lines in the images - I didn't see it in the dark frame unless I overlooked it. I did notice that the dark frame was at ISO 100 and the rest were at ISO 1600. I would redo the dark frame test at 1600 - I would also suggest you do a semi-dark frame where you perhaps take a shot in the almost dark to see if that triggers it more than the complete darkness of the lenscap.
10-06-2021, 11:16 PM - 1 Like   #9
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I looked at DNG files and it seems that there are some problems really. Green and purple lines are not homogeneos. But look how dark frame looks like after exposure +5 eV. Did you tried another SD card to save images?
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10-07-2021, 03:35 AM   #10
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I don't know the exact cause but it's hard to see how it could be anything other than a fault with the sensor. The sensors in the K-7 are (to my knowledge) the worst Pentax have ever used so it's not a surprise to see lines cropping up in shadows.
10-07-2021, 06:49 AM   #11
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QuoteOriginally posted by Jonathan Mac Quote
The sensors in the K-7 are (to my knowledge) the worst Pentax have ever used
The K-7 uses the same sensor as the K20D.
10-07-2021, 07:35 AM   #12
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This is all disappointing. I'm employed at a small cable TV channel and a lot of my work is with video cameras. I enjoy photography as a hobby but haven't had time to do a deep dive into digital photography technology. So, when Medex mentions taking the black image I shot and increasing it by +5eV, it's a little beyond me.

Is this a standard way of testing something? Medex mentions the green and purple lines are supposed to be homogenous -- I guess a link to a black image that looks right would help me. Medex also mentioned using another SD card -- that could make a difference?

Jonathan Mac says the K7 sensors are the worst Pentax ever used and that's shaking my faith in Pentax because I have a K50 that has the infamous black frame/aperture block failure, (I sent it to the company in California that fixes the problem and it cleared up for a while). I was happy with the iST D that I had, last I heard, it was continuing to work for the family member I gave it to.

If the sensor is awful, is there a fix/replacement, or do I just "eat" another bad Pentax, (I bought it used, thankfully). I've been cynical about Nikon and Canon because of the cost of trying to get into their good/better cameras and lenses but now I don't know what to think.
10-07-2021, 08:12 AM   #13
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QuoteOriginally posted by tallytvguy Quote
This is all disappointing. I'm employed at a small cable TV channel and a lot of my work is with video cameras. I enjoy photography as a hobby but haven't had time to do a deep dive into digital photography technology. So, when Medex mentions taking the black image I shot and increasing it by +5eV, it's a little beyond me.

Is this a standard way of testing something? Medex mentions the green and purple lines are supposed to be homogenous -- I guess a link to a black image that looks right would help me. Medex also mentioned using another SD card -- that could make a difference?
+5ev is just raising the exposure presentation so things that looked black are shown that otherwise would be invisible. A working sensor black frame shouldn’t have any lines on it, though it might have small dots of color distributed randomly.

As for “standard way” maybe. It eliminated the image contribution and allowed us to see the sensor output without any worry over reflections and other image induced factors.

QuoteOriginally posted by tallytvguy Quote
Jonathan Mac says the K7 sensors are the worst Pentax ever used…
If I recall the k20d and k-7 were early examples of CMOS sensors and represent the change from CCD sensors. As such there were growing pains.

QuoteOriginally posted by tallytvguy Quote
…and that's shaking my faith in Pentax because I have a K50 that has the infamous black frame/aperture block failure, (I sent it to the company in California that fixes the problem and it cleared up for a while). I was happy with the iST D that I had, last I heard, it was continuing to work for the family member I gave it to.

If the sensor is awful, is there a fix/replacement, or do I just "eat" another bad Pentax, (I bought it used, thankfully). I've been cynical about Nikon and Canon because of the cost of trying to get into their good/better cameras and lenses but now I don't know what to think.
Repair of the camera is probably not an option. You can try a healing tool in post processing to remove the visible Lines.

All manufacturers have issues. But the k-7 is very old and it is hard to imagine expecting it to work without quirks forever. The k-5 and k-3 have been reliable for most people. But all brands have issues - features and prices should guide you.
10-07-2021, 08:38 AM   #14
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QuoteOriginally posted by tallytvguy Quote
Medex mentions the green and purple lines are supposed to be homogenous.

My observation should be treated differently, but it is not necessarily correct. I did deal with the Pentax sensors when I was trying to make them monochrome and damaged a lot of them. My observation is that damage to the sensor's electronic circuits can result in homogeneous rows of pixels - vertical and horizontal that are white or black. I don't see it on your sensor, so I think those pixels are still working, even though the sensor itself is malfunctioning. This is indicated by a dark frame. There should be no such bands in the normal sensor when the exposure is increased.
10-07-2021, 09:59 AM   #15
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Well, thanks everyone. The K50, I bought new, so it was upsetting to stumble into the aperture block problem. The K7 had a shutter count around 13K when I got it, so it may be up to 16K now, it looked good cosmetically and responds to the various menu commands, etc. I thought I'd covered all the bases.

The weird lines seem to be a) intermittent or b) hard to see under different light conditions when the photo was taken, I guess all I can do is keep observing.
Two questions come to mind from the replies above -

Jonathan Mac said it's not surprising to see lines cropping up in shadows -- are the shadows a common area for problems?

Medex asked if I'd tried shooting the black frame on another SD card? What might that do?
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