Re: What causes this blotching?


dbernaerdt
 

Dan Margulis <DMargulis@...> wrote:

As I noted in the OP, however, I am not going back all the way to *those* good old days--I'm going back, say, five or ten years. Even the best digicams back them often produced noisy skies--but not the blotching effect we're seeing today. And that is rather weird, since the sensor arrays back then were in effect smaller, therefore the dust should have seemed larger.
The sensor array, or "chip size", has mostly stuck with a range of common sizes. What has changed is the higher resolution of the sensors. Smaller photosites have the effect of making the dust larger, but are also less efficient at gathering light than a larger one. While the image processing has improved with regards to noise reduction, I think it is fair to say that a higher resolution sensor is going to produce more noise. Some cameras produce a blotchy effect in smooth areas due to the aggressive noise reduction.

I am not totally persuaded by the "dust" explanation because of this, but also because the blotching position doesn't seem to shift over time. That suggests grease or other liquid that has dried over part of the sensor. Simple dust would, I imagine, be shaken off over time.
If the blotches don't move around, then I'd go with the explanation of foreign material on the sensor. My experience with the built-in sensor shaking cleaning is that the efficiency isn't as great as we would hope. If you travel in dusty environments that material is going to find its way on to your camera's sensor.

I used to own a mid-range zoom lens that produced a "whoosh" as one zoomed to the longer focal lengths. This influx of air into the lens sucked all kinds of junk into the lens and on to the glass elements. Even if you don't change the lens on a DSLR, I wouldn't doubt that small particles are going to get pulled into the mirror chamber and then on to the sensor.

I have noted previously that some camera models claim to have noise-free optics as regards skies, but in fact they are just blurring them. That, I suspect, may account for why these relatively diffuse defects have become more common. But, whether that speculation is true or not doesn't matter. Unless we do a lot of cleaning or by a new camera, we have to know how to use the clone tool.
Can you post an image in the files section that illustrates what you're describing, Dan? That would help clear up the debate.

Darren Bernaerdt

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