K5 sensor overheating/on way out?

Finally did some long exposures with the K5 and ND110 to see if I can jettison the trusty old K10. To my dismay most of the shots had these purple-tinged streaks on them.

I was using live view and electronic level only to compose, then switching LV off. Full exif in images.

Portrait orientation, 73 seconds, ISO 80, B+W ND110, Cokin ND grad, IR 3-sec remote release (no SR), eyepiece not covered

[IMG]http://i140.photobucket.com/albums/r35/digitalCG/Troubleshooting/IMGP3778.jpg[/IMG]

At first I thought it may have been bad luck with reflections or a scratched ND grad so had some lunch, changed location and filter...

Landscape orientation, 102 seconds, ISO 80, B+W ND110, Kood ND grad, IR 3-sec remote release (no SR),eyepiece covered

[IMG]http://i140.photobucket.com/albums/r35/digitalCG/Troubleshooting/IMGP3806.jpg[/IMG]

The two side by side in matching orientation, streaks are in same place which for me rules out any filter/external reflection issues.

[IMG]http://i140.photobucket.com/albums/r35/digitalCG/Troubleshooting/combo.jpg[/IMG]

It wasn't particularly warm out, they're not massively long exposures and there's only a touch of highlight clipping in the second shot - can't be CCD-style sensor blooming. Camera is fine on 'normal' exposure durations, even when overexposed.

Any experts on here have an idea if this is an overheating/faulty sensor?

could be overheating of the sensor,there was debate on this type of thing on the k7



i am not at all sure it is the same thing though.
link

I have done 120 secs with k-r and no probs like that.

Sony flagged an over-heating problem with their cameras/sensors, but it took a lot longer than 70 seconds!

http://www.engadget.com/2010/09/29/sony-a55-a33-video-recording-limited-by-overh...

Any chance it's something to do with interaction between the filters? Coking filters are known to cause purple colour casts.

The marks look like smears; I would have expected sensor issues to manifest themselves as dead straight lines?

Cheers John, I'd seen the Sony heating issues but that seems to be triggered by extended use of video/live view, especially with SR on.

I've used the same lens/filter combo before now with no issues (other than the Cokin cast!) so don't think it's that - in fact I've even used it on the K5 for similar exposures:




Thinking about it I used a cable release for the car shot but that broke - these were the first using IR remote. Will get another cable release and do some more testing, but gut feeling isn't great on this right now

It looks more like reflections from a filter than sensor problems. Try a night shot without filter to see if the problem arises again.

I can't believe the IR remote would have anything to do with it, but..

Don't take this the wrong way, but if this indeed proves to be a camera fault I hope this it's peculiar to your K5 and not indicative of another K5 ice-berg!

I'd like to go along with Yves suggestion, but the marks seem too consistent. I'm guessing if due to reflections you'd see changes depending which direction the cameras facing.

And I've just noticed you apparently changed the filter combo between shots, so not many variables left.

Really like your work, by the way! And as you say, this problem doesn't appear on other K5 shots in your portfolio.

If it was reflections the orientation on the second image would be different

Yves, I cleaned the B+W ND110 and used a different ND grad between shots, in addition to changing location, lighting direction, sensor orientation etc. Reflections would surely have changed, yet those marks remain consistent?

Neither can I, it just struck me as a variable between the car and landscape images, which used otherwise comparable settings. I'll do some more testing the next few days including filter on/off, with lens cap on, cable/IR release etc.

Understood, I'd feel the same and certainly not trying to be alarmist here - mods feel free to take the thread down if that's how it appears - just looking for some sensible Pentax User suggestions. If I was looking to create hysteria there are 'better' forums for that

Did you do a "wet sensor cleaning" before taking those pictures?

I had similar problems with my B+W 10 stop.

I had not used the eyepiece cover, I think that this way well be the problem.

I have tried again, used black cloth, as forgot cover on 2nd outing , no problems .

Hopefully this will stop these problems for you too.

But shot #2 did have the eyepiece covered.

Alig, I'm pretty sure the eyepiece was covered with thick black cloth when I set up down by the lake - it was part of the process I realised I'd missed down by the coast. Did you get consistent patterns regardless of setup?

A quick bulb mode test with lens cap on and eyepiece covered (in warmer conditions than weekend!) seems okay, I'll run some more outdoors when I get a chance and report back - probably be a few days.

I'm thinking the same as Yves on this one.

Looks like possible streaking caused by uneven application of cleaning fluid. The lines are not dead straight and are along the length of the sensor which would be the natural direction to clean rather than across the short way indicating human input. Light scatter on the sensor surface could be polarising along the streaks splitting white light at the purple wavelength just like in a rainbow.

Suggest checking your sensor again with loupe magnifier while shining a torch in at an oblique angle and see if any streaks are noticeable, failing that another wet but even application of the sensor might be needed. Perhaps your sensor cleaning swabs are a little too narrow which could be leading to an overlap streak pattern, a slightly wider swab may be required.

The only issue I have seen with heating in a DSLR sensor manifests itself as 'amp glow' ...a brightening in dark images at one of the short sides of a frame. I have fired off quite a few exposures 30sec to 300sec with my K5 with no sign of problems, in fact surprised how little amp glow is apparent compared to my wifes Canon 20D so unlikely to be a heating issue.

Mike