[tantrix]

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Attaching an image I took last night. Didn't have a tripod and was out of focus. But the artifacts are worrisome. It's a newish Sigma lens and new K30 DSLR. Don't see any particles on either on visual inspection. What do you guys think?

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[jatrax]

Sensor dust. It will not be obviously visible sometimes. Do you have the dust removal system turned on? It should be set to run at start up all the time.

You will get dust in the camera when you change lenses and when you zoom a lens or even focus on most the lens will move air in and out so dust will get in that way even if you never change lenses.

Here is the method I use:
Dust removal procedure in order:
1) Use the camera dust removal system. There is a menu setting to turn on/off. If you have dust run this several times in a row and then check for dust again. I leave mine on "run on startup" and I think that is best so you don't have to worry about it.
2) Use a 'rocket blower' or equivalent to blow off anything the shaker will not get rid of. Do not use compressed air or canned air. Some folks report it is OK to use canned air if you are careful, personally I'm not taking any chances but YMMV. You need to raise the mirror to do this, there is a menu setting for that.
3) Use a wet cleaning kit. This is the last resort, and on two cameras with over 25,000 actuations in all kinds of environments I've never had to use one yet. Get this if all else fails but don't go there unless you are sure you need it.
4) Send in for professional cleaning. Pentax extended warranty (in the US) includes one 'free' cleaning. Not sure about anywhere else.

Easiest way to check for dust is to set your aperture to f/22 or so and take an image of the sky. Dust on the sensor is more visible at smaller apertures.

[tantrix]

Thanks for the detailed answer. I've had this camera for 3 months and not changed the lens since i got it. Weird that it got so many artifacts. Will try all the mentioned methods!

[VisualDarkness]

Welcome to the world of digital system cameras, it's a price we pay for flexibility.

[jatrax]

I've had this camera for 3 months and not changed the lens since i got it. Weird that it got so many artifacts.

Not weird at all. Dust gets on the sensor, just a part of using a DSLR. Changing lens is not the only way to get dust, any zoom lens will suck in dust every time you zoom.

Just turn on the dust removal system and in most cases the problem (mostly) goes away. Only worry about the other methods if you a stubborn spot. On older cameras dust removal was not so good and there were more problems. On k-5 & k-3 it is very good and I rarely see much dust anymore.

[Kozlok]

You obviously live somewhere wet and humid. I'm in Florida, and one thing you get here is wet pollen finding its way onto your sensor. The only product I've found that works reliably on this is the Clean Skies brushes (get them from ebay). You use canned air to blow on the brush, it gets a static charge, and use that to wipe the pollen off the sensor in one motion. Do not wipe a second time. If you feel you need to, blow the brush again before you do. There are two brushes in the kit, the first one is used to clean the mirror box, so that gunk doesn't get on the sensor. A great system, very cheap, easy to use.

HOWEVER: If you think you may have gotten something "hard" on your sensor (actual dirt), do NOT use the clean skies brush right away. Get a Rocket Blower, hold your camera facing the floor with the mirror up, and blow on the sensor with the rocket blower (never use any other air on the sensor!!! The canned air can ruin your sensor). The rocket blower will remove most things that are not sticky, but doesn't do anything against pollen.

When you are done, put a lens on, set it on Av mode, set aperture to the maximum (f16 or f22 or whatever the lens goes to), and set ISO on ISO100 (not Auto ISO). Shoot a picture of something bright and all the same color. Indoors I use a sheet of clean paper, but usually I use the blue sky. Look for spots, repeat the brush as needed. When you see a spot in the shot, remember that the sensor is upside down, so if the dust is on the top half of the shot, it will be on the bottom half of the sensor.

[GibbyTheMole]

You obviously live somewhere wet and humid. I'm in Florida, and one thing you get here is wet pollen finding its way onto your sensor. The only product I've found that works reliably on this is the Clean Skies brushes (get them from ebay). You use canned air to blow on the brush, it gets a static charge, and use that to wipe the pollen off the sensor in one motion. Do not wipe a second time. If you feel you need to, blow the brush again before you do. There are two brushes in the kit, the first one is used to clean the mirror box, so that gunk doesn't get on the sensor. A great system, very cheap, easy to use.

Yep... Same method I use. Safe, easy, and effective.

[Des]

The only product I've found that works reliably on this is the Clean Skies brushes (get them from ebay).

Cleanskies Sensor Brush Cleaning Set for Digital SLR APS C and Full Size Sensors | eBay
(Strangely listed as auction without a "Buy it now" price.)

[tantrix]

Thanks for the link!