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11-13-2015, 09:21 AM   #1
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What's optimal way to test sensor for dust-like particles

Today I read this old thread and many comments about sensor problems in early series of K5. Exiftool tells me that my second hand K5 is produced the 23rd of Oct 2010. Serial number is 38619X. On this list of serial numbers I can see many other menbers of this forum mention stain problems with serial numbers close to mine.

I've not noticed anything. Nor have I made any professional test. What's the optimal way to check my camera for stain(s)? Up in the northern Norway blue heaven is uncommon these days of the year. White paper on the wall, hang up the paper in front of a reading lamp or? Is 35mm 2.4 optimal or? Iso 80? Clean computer screen or software-test?

11-13-2015, 09:26 AM   #2
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Use any lens you want, but recommend one that can close to F32. (F22 will work if that's the best you can do). Aim at a cloudless, clear blue sky shoot with sun at your back. (Though I suppose any evenly lit mid-tone target will do, given that you are in Norway and may not see the sun again until June...)

Every spec of dust will show up, trust me.
11-13-2015, 09:27 AM   #3
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try a white or light colored wall and small aperture (e.g. f22). If your sensor has stains it will be obvious.
11-13-2015, 09:29 AM   #4
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Best way is stopped way down, perhaps f/16 or more. Shoot a clear blue sky (without birds) or a plain wall without any dust specks. Shoot a series of a wall with some movement of the camera between shots. If there are any specks on the wall they will move, specks on the sensor will not move.

I suspect if you have the original k-5 sensor issue it would be quite noticeable. I never had it but I understand it was not hard to see.

11-13-2015, 09:49 AM   #5
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I use a white screen on my computer monitor. Stopped down and at iso80. The exposure is usually long enough that camera shake makes sure everything but the sensor dust gets blurry. I usually meter at about +1EV for this, then exaggerate the contrast with a quick levels adjustment to make the dust standout.

Stopping down all the way of course finds more dust, but can also drive you batty. I rarely shoot above f/16 in normal use, so if it takes f/22 or f/32 before a piece of dust starts to be visible in a torture test, I tend to not worry about it. Most of my dust testing consequently happens at f/16.

I don't know about the earlier iterations, but the anti-dust features of the k5iis awesome. They are way, way, way better than my old k100d, which had no anti-dust measures. I've had to do a wet clean on my k5iis twice in almost two years, I used to do the k100d every couple months.
11-13-2015, 10:14 AM   #6
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Why close to f32 and not e.g. according to the MTF program line (sharpest)? DOF doesn't matter on a plane wall.
Perhaps the white wall of my refrigerator or washing machine. By wireless flash. A small piece of red tape on the wall. If I find some suspect dots then I'll see where in relation to the red tape. Or is focus to infintity also a "must"?
I hope you're right, Jatrax - that it was not hard to see. In such case, no problem.
11-13-2015, 10:49 AM   #7
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QuoteOriginally posted by Dabola Quote
Why close to f32 and not e.g. according to the MTF program line (sharpest)? DOF doesn't matter on a plane wall.
The wall is coincidental and may be be out of focus. The same is true for MTF, diffraction and whatever. What you want to do is create the sharpest shadow of the dust at the sensor. A small aperture accomplishes that.


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11-13-2015, 10:51 AM   #8
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QuoteOriginally posted by Dabola Quote
Why close to f32 and not e.g. according to the MTF program line (sharpest)? DOF doesn't matter on a plane wall.
The thing you're aiming at doesn't need to be in focus at all - the more you stop down, the more the dust will show up. This is why your actual usage should influence how you test. For example, if all you do is shallow DoF portraits, dust won't show up nearly as much as someone who shoots landscapes and regularly shoots at f/11 or higher and also includes lots of nice sky where dust stands out. I wouldn't bother hunting for dust at f/32 if it's unlikely to ever impact your real world usage but everyone's real-world usage will vary.

11-13-2015, 11:33 AM   #9
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Now I understand... Of course, the wall of my washing machine or the sky doesn't matter. What I want to grab is the dust. The wall is just the background. As you said, Stevebrot, I wan't to "create the sharpest shadow of the dust at the sensor". Tomorrow I'll make a test by BrianR's method; Tripod + white screen on my computer monitor.
11-13-2015, 11:50 AM   #10
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QuoteOriginally posted by Dabola Quote
Tripod + white screen on my computer monitor.
Don't bother with a tripod- a bit of camera shake is fine. The dust moves with the sensor, everything else can be blurry.
11-13-2015, 11:58 AM   #11
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One trick I learned, which helps me find dust spots I might have overlooked, is using the masking tool in Lightroom. On a Mac, hold the alt key and start dragging the slider to the right (holding the Alt key turns the screen to white until you start dragging and masking sharpening in the background). You'll mask everything but the dust spot and you know exactly where to look (they'll jump right out). Of course you need Lightroom.
11-13-2015, 12:49 PM   #12
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QuoteOriginally posted by jrpower10 Quote
One trick I learned, which helps me find dust spots I might have overlooked, is using the masking tool in Lightroom. On a Mac, hold the alt key and start dragging the slider to the right (holding the Alt key turns the screen to white until you start dragging and masking sharpening in the background). You'll mask everything but the dust spot and you know exactly where to look (they'll jump right out). Of course you need Lightroom.
The "Visualise Spots" check box in the LR6 spot removal tool works great for this too.
11-14-2015, 08:41 AM   #13
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QuoteOriginally posted by BigMackCam Quote
The "Visualise Spots" check box in the LR6 spot removal tool works great for this too.
+1 on this, best tool by far.

To the OP, don't over think this, it is not like checking for autofocus fine tuning. Just find a blank wall, stop down and shoot. Check the image in Lightroom using the visualize spots tool if you have it. Don't spend time looking for spots that are not noticeable, if they are there they are quite easy to see.
11-14-2015, 12:51 PM   #14
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QuoteOriginally posted by BigMackCam Quote
The "Visualise Spots" check box in the LR6 spot removal tool works great for this too.
That's one I didn't know. Assume it's also in Lightroom CC. Thanks for that.
11-14-2015, 01:55 PM   #15
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QuoteOriginally posted by jrpower10 Quote
That's one I didn't know. Assume it's also in Lightroom CC. Thanks for that.
You're welcome Yes, it's also available in LR CC.
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