[Richter]

Ordered a K5 tonight - want to check the sensor to insure I get an un-stained version. Can some one describe for me (in laymans terms) the correct \ process to check for stains on the sensor?

[kittykat46]

My simple checking process.

Set to low ISO - to rule out any other noise sources.
Set the Exposure mode to Av - aperture priority
Set Aperture to f/22 or higher f/number if your lens takes that.
Set to Manual focus - then focus on Infinity
Point the camera at a clear blue sky or blank wall if you are indoors. Basically any featureless scene would do.

Take the shot. Don't worry about the long exposure time if you are indoors - camera shake has no effect on the results since the defect (if it exists) is sitting on the sensor.

If you have any stains/ dust spots etc. on your sensor, it will show clearly against the blank background.

[Miserere]

You can read the following section of my K-5 review for a short tutorial and examples of what to look for:

The K-5 Sensor Stains

...

[sjtryon]

This is VERY helpful! Thank you.

Sadly, the results of following your instructions revealed that my K-5 does have stains on the sensor. Now I am debating whether I take the device through the warranty process or run it back to Amazon (my point of purchase) where a new camera will be sent right away, even before I send this camera back.

Any thoughts from anyone about that?

Thanks.

Steven

[robgo2]

Sadly, the results of following your instructions revealed that my K-5 does have stains on the sensor. Now I am debating whether I take the device through the warranty process or run it back to Amazon (my point of purchase) where a new camera will be sent right away, even before I send this camera back.

At this point, we don't know whether Amazon and other retailers have checked their inventory of K-5s and weeded out those bodies that have the defect, which means that your replacement camera may have the same problem. OTOH, Amazon offers free shipping for return and replacement of defective products, so I don't think that you have anything to lose by going that route. It's what I would do. The word from China is that Penax is already replacing bad units with good ones, so they seem to be responding appropriately.

Rob

[sjtryon]

Thanks, Rob. Thinking the Amazon return is what I will do...

[Matt Miller]

Set to Manual focus - then focus on Infinity

Why focus at infinity? Wouldn't minimum focus distance be better?

[novsky]

Why focus at infinity? Wouldn't minimum focus distance be better?

U can even do it without any focus, and moving the k5, because stains are on the sensor not on the sky or a wall

[kittykat46]

Why focus at infinity? Wouldn't minimum focus distance be better?

Here's the optical theory

The best way to make visible very small items sitting on the sensor (or thereabouts) is to have the light falling on the sensor
1) As close as possible to parallel,
2) As close as possible to a uniform , featureless background

(1) Is achieved by setting to the smallest possible aperture (f/22 or more) and by focusing the lens on infinity.

Focusing on Infinity also helps (2) by blurring out most remainding details in the scene.

The opposite logic applies to avoid seeing the stains.
Larger apertures (below f/16 with the sensor stains I have) or focusing on closer objects will make the stains invisible or nearly so. Both methods cause the light falling on the sensor to arrive at more acute angles, depending on which part of the lens surface captured the light.

For me personally, that's actually most of the real-world photography that I do, which is why I'm still happily using my K-5 unit, until Pentax sorts out the solution.....

[Matt Miller]

So it's not like seeing dust on a filter, where a closer focus point would show it more clearly?

[kittykat46]

So it's not like seeing dust on a filter, where a closer focus point would show it more clearly?

Yes, the optical effect we are trying to achieve in this case is quite the opposite

[vario]

Instead of sending my camera back for a replacement, i chose to send it to Pentax for repair. This is the only way i know of getting a unit guaranteed clean. If Pentax is not checking the unit before sending it out, shame on them, but i have to believe this is not the case and it would be a good unit.

[Rainer Dynszis]

Here's the optical theory

The best way to make visible very small items sitting on the sensor (or thereabouts) is to have the light falling on the sensor
1) As close as possible to parallel,

I don't think so. The "optical theory" is that you can calculate the distance from obstruction to sensor by evaluating the difference between umbra and penumbra at f=22 or thereabouts. If the difference is small, you have a problem, because that means it's sitting on the inside. If it's big, or no umbra at all, you have dust.

If you have "parallel" light falling on the sensor, you have no penumbra to evaluate.

[Richter]

Thanks to all for your responses to my question. I recieved my K-5 on Friday and tested it as suggested above and my K5 (SN 3865823) clearly has the sensor stains in the center of the sensor. Loaded info into Pentax Forum SN database.

Plan to return for exchange.

[Digidoc]

The best way to detect dust is explained on page 341 of the manual (Dust Alert). Claening the sensor can be done by using a SensorSwab. Dry to start with and if no success then again with the Eclips liquid.