I have an issue with purple noise in the top right corner of the sensor on low light / long exposure images. The issue was noticeable enough to cause problems while shooting the Milky Way this weekend on the night of the new moon.

 

Has anyone seen this before? The image below was shot with a cap over the sensor, and the camera under a pile of blankets.

 

Thanks!

 

 

 

 

Maybe this corner is nearest to the

hottest section of the battery and so

it goes more crazy noise-wise ?

  

If you could use a remote power

source with a cable feeding into a  

a dummy battery and it made the

effect go away, that would confirm

that this is due to radiant heat from

the internal battery.

Looks more like a light leak. Try covering the lens/mount with a cloth and see if it still appears.

Hi all, thanks for the responses.

 

Golem - The image would seem to indicate that the noise occurs on the bottom left of the camera sensor when viewed from the back, which is opposite the battery. The best test I can run is as follows: I left the camera off for a few hours and took another picture, but the issue persisted.

 

RightAngle - As mentioned in the original post, the image was taken under a pile of blankets. To be doubly sure, I repeated the test in a dark room with the lights off, again under a pile of blankets. The problem persisted. I also tested at an iso of 50, and it was still there (albeit very faint).

 

Note that I'm shooting in raw, uncompressed, manual, 30s exposures with auto iso. I have to shoot in full frame mode, as the problem is cropped out in Super 35. I've also tried turning off Steady Shot and Long ExposureNR, but the problem still presists.

 

Thanks for the input! Keep it coming!

Does this noise still occur when you have long exposure noise reduction set to on?

Take a good long look at the sensor itself. Had a fingerprint on mine after a lens change. Coming from mirrored cam I thought no big deal but closer inspection of pics showed slight variation due to (I presume) fingerprint grease affecting temp/clarity of the sensor transmitting data. This portion of sensor might have a similar smear which, especially on extended exposures, doesn't dissipate heat as uniformly as the clean sensor. I use a 14x jewelers loupe to examine the sensor for dust & specks that will go unnoticed using the naked eye.

duncanfoxphoto - Yes, it still occurs. I had the same thought and checked for this - I would have expected NR to knock it out, but it would seem that it's not seeing the noise on the dark shot - perhaps the issue is further upstream? The noise appearing immediately after turning the camera on would also imply to me that it's not a heat noise issue, but perhaps there are some other electronics inside the camera that heat up faster than the sensor and are poorly shielded. I'll try putting the camera in a dark place with the cap on and taking a timelapse tonight to see if the problem worsens.

 

VTC - I had a look at the sensor last night with my naked eye and a flashlight - there were a few dust specks but nothing major. I'll have another look tonight when I get home and give it a go over with a blower. Good call on the loupe! 

Looks more like a light leak. Try covering the lens/mount

with a cloth and see if it still appears.

   

Did you read the below, in the OP ?

 

"The image below was shot with a cap over the

sensor, and the camera under a pile of blankets."

Hi all, thanks for the responses.

 

Golem - The image would seem to indicate that the noise

occurs on the bottom left of the camera sensor when viewed

from the back, ........

  

Not sure what you are describing now, location-wise.

In the OP you say "I have an issue with purple noise

in the top right corner of the sensor".  

   

To be sure we're on the same page, let's agree that

what is seen on the left side of the rear LCD panel is

the edge of the sensor nearest the battery, and what

you see at the top of the LCD panel represents the

bottom edge of the sensor.

Not sure what you are describing now, location-wise.

In the OP you say "I have an issue with purple noise

in the top right corner of the sensor".  

   

To be sure we're on the same page, let's agree that

what is seen on the left side of the rear LCD panel is

the edge of the sensor nearest the battery, and what

you see at the top of the LCD panel represents the

bottom edge of the sensor.

 

Whoops! My apologies, the image in the OP is unaltered. The appropriate left/right and top/bottom transformations from image->sensor apply as per your comment.

 

I was trying to convey that the noise is opposite the battery location, as the battery is located in the grip on the right side of the camera when viewing the LCD panel. Since the noise is on the top right of the image, the physical pixels are on the bottom left of the sensor when viewed from the rear LCD panel, away from the battery.

Here's a snip of timelapse from last weekend (played back and forth a few times). Note that since this was taken with the timelapse app, it's made out of JPG's (I don't understand how building an app that only saves jpeg's could be a good idea). The shots were taken during a new moon, so it was really dark.

 

Exposure is boosted and contrast brought down to show the issue a bit better. The sequence is 28 images long, 25s exposures with long exposure NR, so the length of each segment in the video (again, it's playing back and forth a few times) takes up around (25sec exposure + 25sec NR) * 28 images = 23 minutes (+ a few seconds between each exposure, not sure how long but it was set to minimum). The camera was used for roughly an hour on and off before this sequence, so the sensor was already somewhat warm.

 

https://www.youtube.com/watch?v=oyMGGSJ8ap4&feature=youtu.be

That is a very unique fault in the camera. You may just have to send it back to Sony for repairs. You haven't mentioned this, but I assume you have ruled out the lens by testing with another? It certainly looks more like a sensor issue, but who knows with the amount of electronics in these things these days.