Odd 'shadow' on images - any suggestions?

[pgk]

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So here's an odd one. Occasionally I get an odd dark patch on images from my M9. Its very unpredictable and relatively rare but it does occur at times. I think it is going to have to have a trip to Germany unfortunately, but I'm baffled as to its cause. Sometimes its on only one frame with several similar frames before and after. Sometimes its on several. It affects perhaps one in several hundred images and appears most (or is most noticeable) in slightly underexposed mid-tones such as blue skies, but not always. I wondered if it might be an area affected by something such as my grip or whatever but its too inconsistent. Most of the times its not a problem and can to a large extent be dealt with in PP though this isn't ideal. Comments welcomed.

 

Pix showing the problem:

 

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[pgk]

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[earleygallery]

Have you tried cleaning the sensor? Probably an oil spot rather than dust. 

[pgk]

Have you tried cleaning the sensor? Probably an oil spot rather than dust. 

Its happened prior and after cleaning and is completely intermittent. I can see nothing whatsoever on the sensor.

[pop]

The spots exhibits some of the characteristics of sensor dirt, but it's rather faint, rather large and not as clearly delimited. Is it possible that you can see it only when the lens is somewhat stopped down and the image area is void of any details? The aperture seems to be between f:8 and f:11 in all the samples provided.

 

Have you inspected the lens, in particular the rear side?

[wattsy]

I remember Jimmy Hughes (Leica UK customer care), when inspecting my Monochrom sensor, was struck by a similar shadowy 'blob' in the test images he was looking at. He was able to move the shadow in the test images by loosening the lens in the mount and rotating it. He thus concluded that the 'shadow' was likely caused by dust inside the lens rather than on the sensor. Presumably the right combination of light, aperture, focus distance all comes together on occasions for the dust to be able to cast this magnified shadow.

[pgk]

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Its not just on one lens so isn't the lens.

[earleygallery]

It must be the sensor then. Are you sure you can't see anything on the sensor at all (remembering the image is inverted!).

 

It doesn't look like the sensor corrossion issue but if cleaning doesn't work I think the only thing you can do is return the camera to Leica for inspection.

[pico]

Interesting. Can you make a test by shooting an evenly lit grey card without lens, or with the card entirely out-of-focus?

[pgk]

Interesting. Can you make a test by shooting an evenly lit grey card without lens, or with the card entirely out-of-focus?

I've tried to 'force' the camera to show the shadow (as per some of the posted images) - the trouble is the intermittency of the shadow - it is only occasionally that it appears. Sometimes it does so on a number of adjacent images, at others it does once and very similar adjacent images show nothing. Which is why I posted - its difficult to get the camera to show the 'problem' which does occur most on slightly underexposed areas of reasonably continuous mid-tone, but far from always. There is absolutely nothing to be seen on the sensor and I'm really puzzled as to the cause which I've tried to ascribe to possibilities such as my thumbgrip (localised warming of the sensor) or some other logical problem but to no avail. I rarely see it to be honest, but its there. I'll see what I can do.....

[pico]

A real mystery. Please keep us informed.

.

[pop]

If it really happens with different lenses: could you try and open an original file with another program which can display DNG files? I'm trying to establish that this is not some weird kind of processing you inadvertently placed as a default action into your PP software. Far-fetched, but stranger things happen.

[wattsy]

Its not just on one lens so isn't the lens.

 

 

Maybe you just have more than one lens with dust inside? Is it always in the same place, irrespective of lens used?

[Erik Gunst Lund]

A smudge on the rear element of a lens can make a dark spot like this, but yes that would indicate that it was only with one single lens,,,

[250swb]

Got any filters on the lens, something like a damaged polarising filter?

 

It may be worth massively increasing contrast in Photoshop/Lightroom to see if any structure appears in the blob.

 

 

 

Steve

[hepcat]

I've tried to 'force' the camera to show the shadow (as per some of the posted images) - the trouble is the intermittency of the shadow - it is only occasionally that it appears. 

In order to see if you can duplicate this on demand for troubleshooting the problem, you'll need to approach it systematically. It would be most helpful to start with photographing an 18% gray card using a fixed ISO and at various apertures with the lens you use most.  Include any filtration you use regularly, and then test excluding it.  Then move on to the other lenses you use most frequently.  Record each exposure and see when a pattern emerges with the lens/aperture combinations to see if there is any correlation to a particular lens, a particular aperture, or a particular combination.  The process may take you a while, but it may help you get to the bottom of the problem. 

[Schrödinger's cat]

As I don't know what method you used for cleaning, I'm going to vote for something smeared on the sensor.  I can almost see something being deposited by a greasy gel stick or something of that nature.  If you did not wet clean then that would be in order.  If you did wet clean, I would suggest doing so again with one of the other wet cleaning fluids.  Some seem to be better than others with particular materials.

Edited October 16, 2015 by Schrödinger's cat

[250swb]

As I don't know what method you used for cleaning, I'm going to vote for something smeared on the sensor.

I think you may be onto something. The M9 is an oily camera, the shutter has always thrown off oil although it does calm down after many shutter actuations. In previous cleaning (of which we are not sure of the technique) an oily spot may have been smeared around. What is needed is a wet cleaning fluid that shifts oil, Invisible Dust 'Smear Away' is one product.

 

Steve

[pgk]

Thanks everyone. I've never wet cleaned the camera and the 'shadow' goes back to when I first got it (ex-demo) but is only visible very occasionally. As its not really a big deal I'll ship it to Leica sometime when I can spare it. For the last few hundred shots it hasn't shown up at all so I'm still baffled.

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