Weird Blue cast.

[HenrikP]

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Hi all.

 

Hi all, I took a backlite picture, where I experienced a strange blue color cast. it is not so much the color cast, as is the sharp edge. It is taken with a M-E with a 50mm summarit 2.4. Can the edge be due to the lens hood?

 

Regards Henrik

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[pechelman]

It could be since the hood on this one is actually sort of square (unlike the APO 50), but there was a recent discussion in that thread about a similar horizontal line as yours. In that case it was determined to be reflections inside the camera. The camera internals then also block some of the reflected light on the bottom edge of the sensor nearest the reflection. Though unless you're showing us sort of a before vs after / left vs right comparison, I'm not sure that would explain the vertical separation line.

 

Here's the link to the original discussion in another 50 APO thread about flare;

http://www.l-camera-forum.com/topic/208297-apo-summicron-502-asph-central-veiling-flare-fogging/page-9

See post 161. Also go back a couple of pages for similar examples as yours.

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[TomB_tx]

I've seen similar effects in different colors when there is a strong light source in the image that way overblows the sensor output. Even though the rectangular area you notice extends way outside of the blown highlight, it seems blocks of cells on the sensor are affected by such an overload.

Digital sensors do strange things with intense light sources.

[jaapv]

This is a centrefold issue, where one half of the sensor reacted differently from the other, possibly in the motherboard. Send the file to Leica for advice.

[pop]

This is a centrefold issue, where one half of the sensor reacted differently from the other, possibly in the motherboard. Send the file to Leica for advice.

Either that, or a case of blooming where an extremely bright part of the picture is just beyond the image frame but  still on the sensor.

[adan]

On pop's theme - this looks exactly like the "green band" problem of the M8. The sun's image or bright light exactly on the edge of the CCD, top right, is leaking into the "black reference" pixels around the edge of the sensor, fouling up how that part of the image is then interpreted and digitized.

 

See bottom of the page here (post #40) - http://www.l-camera-forum.com/topic/68490-m82-failure/page-2

 

On jaap's theme - correct, the sensor output is "read" out of both sides at once - half the picture <[  |  ]> to each side - to speed up the output. Therefore the "green band" stops halfway across - the sun glow only affects the data from the right side of the sensor, and you see the sharp edge at the joint in the middle.

 

When the M9 came out, the very first thing I did was test for this kind of banding on the larger CCD - I could not reproduce it then, and have never seen it since. The M-E uses the same M9 CCD sensor, although perhaps not exactly the same, if it has the new corrosion-resistant-cover-glass sensor.

 

Follow-up: The M8 produced the green bands because it used the nominally 1.3x-crop sensor from the DMR digital back for the R8/9, but "cheated" the crop factor out a bit to 1.33x. Which mean the black mask that protects the "black reference" pixels from light (so that they can read "black") no longer had as much safety margin, and very intense light falling right on the mask could leak to the reference pixels.

 

One wonders if - in revising the 24x36 CCD to add the new anti-corrosion glass - a similar design error crept in. Or perhaps this is just a one-off problematic sensor. I guess anyone with the new CCD could test for that.

Edited August 28, 2016 by adan

[mjh]

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Assuming it is a one-off phenomenon this is surely related to the infamous green stripe issue of the M8. This can also affect the M9 and M-E although incidents are much, much rarer. Taking the picture again with the light source in a different position – either clearly outside or within the frame – should do the trick.