Can anyone tell me what these circles are?

GeneV · 12-16-2008, 10:20 AM

I may be showing my digital ignorance here, but can anyone tell me what those two circled darker spots in the blue sky area are? The most noticeable one is just inside the palm tree trunk on the right. They appear, if at all, regardless of the lens.

felix68 · 12-16-2008, 10:25 AM

That is dust on your sensor. Time to try sensor shake cleaning, rocket blower, etc to try and dislodge it.

GeneV · 12-16-2008, 10:29 AM

Thanks. That was my initial thought.

tbone-ike · 12-16-2008, 11:36 AM

I thought they were UFO's in the sky. Glad to hear it's only dust!

kerrowdown · 12-16-2008, 12:32 PM

Only dust I'm afraid, a bit of blowing or photoshop sorts 'em out.

Had they really been UFO's, that shot would have been worth big money.

dosdan · 12-16-2008, 12:45 PM

They seem a bit large for dust. I had similar spots on my K100D Super after I changed lenses in slight rain and I believe they were caused by dried rain drops (the rain is not pure water).

See the example I posted a bit down in this thread compared to a dusty sensor example:

K100D Sensor Dirt.......

I was able to finally remove it by using a Pentax sensor cleaning kit (expensive but effective). I described how to fix up affected photos in the healing section of this tutorial:

http://www.pentaxforums.com/forums/p...-cropping.html

The following video shows someone using the Pentax O-ICK1 Image Sensor Cleaning Kit to clean a Nikon sensor. It helps to see it in action to learn how to use it properly:

YouTube - Pentax O-ICK1 Image Sensor Cleaning Kit

Dan.

GeneV · 12-17-2008, 07:43 AM

Originally Posted by dosdan

They seem a bit large for dust. I had similar spots on my K100D Super after I changed lenses in slight rain and I believe they were caused either by dried rain drops (the rain is not pure water).

See the example I posted a bit down in this thread compared to a dusty sensor example:

K100D Sensor Dirt.......

I was able to finally remove it by using a Pentax sensor cleaning kit (expensive but effective). I described how to fix up affected photos in the healing section of this tutorial:

http://www.pentaxforums.com/forums/p...-cropping.html

The following video shows someone using the Pentax O-ICK1 Image Sensor Cleaning Kit to clean a Nikon sensor. It helps to see it in action to learn how to use it properly:

YouTube - Pentax O-ICK1 Image Sensor Cleaning Kit

Dan.

Your shots do look closer to mine, though what is different about my spots is that they appear to be perfect circles rather than flecks or blobs. I gave it a shot of air, and i don't seem to see them now, though I need a clear blue sky (it's snowing here) to give it the acid test.

mysterick · 12-17-2008, 08:15 AM

Shoot a white sheet of paper and see if...

ManuH · 12-17-2008, 08:28 AM

Shoot at f22 a wall or a sky, unfocussed and SR off (the more the blurr the better, if there is dust on the sensor, it will stand out). Even with the K20D I do that (the dust alert doesn't work that well IMHO).

What I do to clean: a rocket blower first. If this doesn't work, the Pentax O-ICK1 kit, very effective for sticky dust.

kevbirder · 12-17-2008, 10:46 AM

People keep recommending rocket blowers but every time I use one I end up with more dust on the sensor than when I started. I guess it shifts all the dust in the body, not just that on the sensor.

The picture shown looks just like the dust I have seen and the only way I could remove it was with a chamois pad on a stick (designed for cleaning video recorders) and isopropyl alcohol. It's a bit scary especially doing it the first time. First time I tried, some of the dust must have been a bit greasy and it smeared all over the sensor. After repeatedly cleaning, the smears went away and it ended up clean.

I have found that with a strong bright light at an angle and good reading glasses, you can see the actual dust on the sensor without having to take test pictures just to see if you have successfully cleaned it.

Incidentally does anyone know if the shake reduction mechanism on the latest cameras makes this cleaning more likely to do damage? Hopefully it is required less anyway.

GeneV · 12-17-2008, 12:22 PM

The weather finally cooperated and I got this shot. It looks like my blast of air got them. I've goosed the contrast way up, which is how they showed up most in my shots from Florida.

pop4 · 12-18-2008, 12:16 AM

Looking good, now try a shoot at say F/11 and then F/22. The above shot was taken at F/5.6, but your original shot was taken at F/8, and smaller apertures will tend to show up dust bunnies a lot more.

Personally, if my sensor looks clean at F/11, then I'm happy; I don't bother trying to get a clean sensor at F/22, since I rarely shoot at more than F/11 anyway.

GeneV · 12-18-2008, 05:56 AM

Originally Posted by pop4

Looking good, now try a shoot at say F/11 and then F/22. The above shot was taken at F/5.6, but your original shot was taken at F/8, and smaller apertures will tend to show up dust bunnies a lot more.

Personally, if my sensor looks clean at F/11, then I'm happy; I don't bother trying to get a clean sensor at F/22, since I rarely shoot at more than F/11 anyway.

Interesting observation about the aperture. I hadn't thought that would matter, but now that you mention it, my program line on the day that I noticed all these circles was for MTF, and that seems to mean my K10d tries to maintain F/8 about 90% of the time. I've gone over the raw shots again, and the circles are, in fact, much more visible at F/11 and much fainter, though still discernible, at 5.6. (All the shots with the circles in the sky were at F/5.6-11)

I'll see if the weather cooperates again today for another test.

alohadave · 12-18-2008, 07:16 AM

Originally Posted by GeneV

Interesting observation about the aperture. I hadn't thought that would matter, but now that you mention it, my program line on the day that I noticed all these circles was for MTF, and that seems to mean my K10d tries to maintain F/8 about 90% of the time. I've gone over the raw shots again, and the circles are, in fact, much more visible at F/11 and much fainter, though still discernible, at 5.6. (All the shots with the circles in the sky were at F/5.6-11)

I'll see if the weather cooperates again today for another test.

They will be much better focused as you close down the aperture. Shooting at f/22 will usually allow you to see the exact shape of the dust (in the case of hair and fibers).

Remember that the sensor is inverted horizontally and vertically from what we see, so if you are trying to clean a particular spot, you'll need to account for the flip.

pop4 · 12-18-2008, 09:33 AM

Originally Posted by GeneV

I'll see if the weather cooperates again today for another test.

You don't necessarily need to wait for clear blue skies for the test. Any bright, even coloured surface should work; I use my computer monitor set to display all white (I open up Paint, set the Width and Height in Attributes to bigger than my desktop resolution, and then go to View Bitmap). Just make sure that you've got it on manual focus so that the monitor/surface is not in focus when you take the test shot. Moving the camera around, whilst keeping it pointed at the test surface, also helps.