[felipeamaciel]

Hi. About a month ago I bought a Sigma 18-50 lens for my K-50 and I got some weird dark spots in some pictures. I asked myself already if the problem was dust in the camera sensor, but the other pentax lenses I own work fine and I dont get any problem like this. Does anyone has any idea why is this happening? Should I send the lens to a repair service?

Thanks.

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Last edited by felipeamaciel; 09-21-2017 at 08:06 AM.

[pepperberry farm]

looks like spots on the lens - have you done a good wipe-down/blow-out of the lens?

[felipeamaciel]

looks like spots on the lens - have you done a good wipe-down/blow-out of the lens?

yes, I tried this already and I still get these spots.

[pepperberry farm]

yes, I tried this already and I still get these spots.

is this a new or used lens?

if the spots don't show up with any other lenses, it's not the camera sensor... can you see any debris/spots if you shine a flashlight through it?

[Basie]

If you are using the lens on small aperture the dust would be more visible. Might be why you do not see in on the other lenses. It is highly improbable to come from the lens itself

[geomez]

I believe it's dust/debris on the sensor. When I get this I first use in-camera dust removal. If that doesn't work I put the camera in sensor cleaning mode, which puts up the mirror and opens the shutter. I hold the camera with the sensor facing down and and shoot air onto the sensor with a rocket-type blower. If that doesn't work, I clean the sensor with a gel stick. Those steps have always worked for me.

[CarlJF]

These obviously are UFOs flying in formation using dust-looking stealth technology. Put them on Instagram, they will go viral and you'll get famous and maybe even rich!

[pschlute]

Really does look like sensor dust-bunnies. Check your other lenses with a bright blue sky at smallest aperture ...f22 ish

[Alex645]

I believe it's dust/debris on the sensor. When I get this I first use in-camera dust removal. If that doesn't work I put the camera in sensor cleaning mode, which puts up the mirror and opens the shutter. I hold the camera with the sensor facing down and and shoot air onto the sensor with a rocket-type blower. If that doesn't work, I clean the sensor with a gel stick. Those steps have always worked for me.

+1 on the advice quoted. Typically you will only notice dust on your sensor at small apertures in the f/11-f/32 range and in featureless skies or walls.

My only added suggestion when cleaning is to have the lens off and camera pointed down, so the dust can fall off and out of the camera when using a rubber bulb blower.

When you shoot a white wall at the smallest aperture (f/22, f/27, etc) (any shutter speed for normal exposure), do the spots not appear on your other lenses? When you shine a flash light into the lens, do you see anything on the elements that could cause this?

[Adam]

It's much harder for dust in the lens to show up in photos, so as a first step I'd give the sensor a good cleaning.

[biz-engineer]

It is very likely dust on the rear element of the lens.
Dust on the front element aren't see as discrete since they are largely out of focus, they affect MTF.
Dust on sensor show as net dark particle in the image, can look like a hair or something similar.
Dust on the rear element of the lens look like grey fuzzy rounds in the images.

[felipeamaciel]

Those images are taken at f/3.5 and f/5.6 There's absolutely no way the light is collimated enough at such a wide aperture for rear element dust to show up so obviously on a lens of that focal length.

Definitely sensor dust.

thanks for the help. I tried cleaning the lens and the sensor with a blower, but I'm still getting these dark spots. I guess I'll try to clean the sensor professionaly.

[sealight]

I lately faced a similar problem- and while I'm still not 100% sure I solved it fully, as sometimes it's a mix of different reasons- in my case the main problem seemed to be caused by my polarisationfilter, seems these spots are generated in between the two glasses of the filter....kinda weird, and still under observation....

[Wheatfield]

Clean your sensor.

[Alex645]

thanks for the help. I tried cleaning the lens and the sensor with a blower, but I'm still getting these dark spots. I guess I'll try to clean the sensor professionaly.

A professional sensor cleaning, from someplace like KEH.com will cost $55 plus shipping or more.

Repair | KEH Camera

Before you do that, you may want to go the next step after trying the Rocket blower and either use a SpeckGrabber Pro kit for $17 (which is ideal if there is a removable particle, like dust, on the sensor) or $22 for an Eclipse wet sensor cleaning system with swabs (better if there is oil, mold, or non-particulate type object on your sensor).

I own and use all three (rocket-blower, speckgrabber, and eclipse swabs and solution) because 90% of the time, they are effective for the problem. Only once did I encounter a student with an old Canon Rebel XT that had a sensor so filthy, it was beyond my ability to clean that sensor.

Just make sure your battery is fresh and NOTHING could accidentally close the shutter and mirror return during the cleaning process. Anything obstructing the focal plane shutter when closing can result in hundreds of dollars of repair.

Kinetronics SpeckGrabber Pro Cleaning Kit KSSGK B&H Photo Video
Photographic Solutions Sensor Swab ULTRA Kit (Type 2) UK2 B&H