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01-03-2010, 03:44 AM   #1
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Small but odd contrast blotches

Hey all, I'm new to these forums and very new to photography. I just got my new Pentax k-x with the 18-55mm kit lens a few days ago and have shot only around 100 shots, so far not too many keepers, haha. Anyway, I decided to have a go at some pp using Picasa and I started to notice some patches in my photos that are constantly darker in contrast than the surrounding area. You can see one fairly clearly in the upper left.

I'm thinking that it may just be dust on the lens or sensor, but again, no experience here and I just want to make sure it isn't potentially anything serious.

Thanks for any input

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01-03-2010, 05:55 AM   #2
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I'm seeing some dust on your sensor.
01-03-2010, 06:13 AM   #3
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I have a k10 and use the dust removal shake on start-up. Your Kx should have a similar feature and I would try that first. You will find the info in your OM I'm sure. If that does not work there are a multitude of threads about sensor cleaning.
01-03-2010, 06:14 AM   #4
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I'd say it's the lens (dust on surface of front or rear element). Blotches or darker areas are defocussed dust pieces - so they must be somewhere away from the sensor. Is this shot trough a car window? Maybe it had some dirt on it.

When they are on sensor they are in good enough focus to be well defined, but much smaller. Depending on their translucency, they show up as much darker and smaller dots, in the size of few pixels. Sometimes they are like small strings. A rocket blower and few dust removal activations make them go away, if there are too many of them.

Usually it's not a big issue. If the image is critical (large print, fine arts, landscape etc) you can clone them away unless there are dozens of them (then you should consider cleaning). Otherwise they are almost invisible, especially if there is something more interesting in the picture to look at, unless your'e specifically looking for them.

01-03-2010, 08:13 AM   #5
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Clean your sensor. You won't ever see dust on a lens surface as a discreet spot under normal shooting situations.
01-03-2010, 03:32 PM   #6
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Thanks for the input so far. I took a test shot at f/40 to see if I could identify where the dust is. It seems like it is the sensor then? Would this product do the job? Giottos AA1900 Large Rocket Blaster: Camera & Photo
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01-05-2010, 02:43 PM   #7
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That should about do it but it is no guarantee.
Some dust sometimes stick and can't just be blown away.
If however, you can't blow it away, you have to clean the sensor surface itself with something more on a "touching" aspect of it like wiping.
There are products being sold to do this if you are brave enough to do it.
I had a similar problem with my K100D super and bought the rocket blower but the dust stayed.
I had to decide to clean it by wiping it with a lens cloth (not recommended if you don't know what you are doing).
There is a product that is being sold as dust-aid although I haven't used it since the price was too much for my sensibility and the fact that I was brave enough to do the alternative (lens cloth).
I didn't wipe the whole surface though, I just detected where the spec of dust was and only wiped that very small part.
I didn't even touch it that hard or long.
01-05-2010, 03:39 PM   #8
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That's dust on the sensor. I used to worry about it but (knock wood) so far I haven''t had any that couldn't be resolved with the blower.


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