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Old 01-11-2019, 07:34 PM
Startrek (Martin)
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Red pixels smeared across sub frames

I was imaging NGC 300 last night with my 8” f5 newt on an EQ6-R mount , everything was going well with 5 minute subs , Canon 600D unmodded DSLR was running ok this time of year at 25 degrees , good PHD2 guiding at 0.80 arc sec , good focus and framing spot on. Got to frame 27 until I hit the meridian, EQMOD automatically put my scope back into park position, I then slewed up to NGC 300 again on the west side , once again good guiding , good focus and framed up well. Then I experienced something I’ve never seen before in 2 years of imaging with this camera , my first 5 minute sub was smeared with red pixels across at least 75% of the frame , histogram showed green and blue ok tall and thin together but red was low and fat to the right hand side. The star field was ok still nice and round and tight and could just make out the galaxy in the background
So tried another 5 minute sub , same thing , tried a 4 minute and 3 minute sub , same issue again but not as severe with the red pixel swarm
The Canon DSLR sensor temperature was exactly the same as on the previous 27 x 5 minute subs on the east side
At first I thought it’s smoke haze but causing the red to blow out but it can’t be as the first 27 subs were fine. Then I thought the camera sensor is stuffed ( maybe ?? )
Camera appeared to be operating ok , no warnings or codes
It was 1.00am and fighting to keep alert so I shut down and went to bed.
This morning I switched on the camera and it came on ok , took a few random shots in the morning without the lens , they were bleached out of course. Had to pack up and leave for Sydney
Any ideas what may have caused the red pixels smear ???
I won’t be using my scope and test my camera again until next week now.
Appreciate any advice on the above
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Old 01-11-2019, 09:14 PM
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Nikolas (Nik)
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need pictures to see what it is
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Old 02-11-2019, 11:29 AM
Startrek (Martin)
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Attached jpeg in reduced size of both sides of meridian
Subs 15 minutes apart between meridian flip
You can easily see the red pixelation on the west side
Sensor temp on camera only 1 degree different

Any ideas ??

Thanks in advance
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Old 02-11-2019, 01:20 PM
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Atmos (Colin)
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That looks a bit like a light leak.
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Old 02-11-2019, 01:26 PM
spaceout
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It looks like that when there are emergency lights on in the distance.


It's too faint to notice with your eye, but will pollute your astrophotography images fairly easily.



It's possible your camera is fine.
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Old 02-11-2019, 01:35 PM
Startrek (Martin)
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What’s got me stumped is the east side with 27 x 5 minute subs are good and after the flip to the west side you get these red pixels , didn’t touch the camera , didn’t touch the scope , no stray light, I was in a good dark place
The before and after we’re the same optical conditions
My only guess is that is just noise ??
DSLRs don’t like 5 minute subs outside winter
It was a warmish night at 20 to 21 degrees C
It’s the before and after that’s a mystery ??
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Old 02-11-2019, 02:01 PM
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Nikolas (Nik)
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maybe your western horizon was not in complete darkness (astronomical twilight) hence the scattered light. What tine was this?
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Old 02-11-2019, 02:03 PM
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Nikolas (Nik)
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Only other thing I can think of is are there any bushfires in the west of the state? Could be red skyglow from distant fires only picked up by camera sensors
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Old 02-11-2019, 02:12 PM
Startrek (Martin)
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Nik
Good points
It was around 1.00am
Bushfires would have affected the first batch of subs ?
Still heading towards noise in the DSLR ??
Thanks
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Old 02-11-2019, 02:53 PM
spaceout
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If you actually had forest fires, then yes I would assume it is emergency equipment that moved into your proximity during your meridian flip.
You can see the gradient to the left of the image, that is where the flashing red lights are. They could be several kilometers away.
On a clear night without direct line of sight that red emergency light will swarm your imaging gear without you being able to see it with your naked eye.
Sure I could be wrong but given the information we have it's the likely scenario until you take another picture to see if it reoccurs.
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Old 02-11-2019, 03:05 PM
Startrek (Martin)
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Thanks Space Out
Good point
We did have fires out west during the day but they were more than 15 or 20km away in a remote area with only fire trail access
I could be wrong but I can’t imagine my camera picking up that red strobe light signal that far away, then again it could be the reason behind the red pixelated subs
Thanks for commenting
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Old 02-11-2019, 06:11 PM
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15-20 kms away will register on a camera that is exposing for 5 minutes for sure, it may appear clear but small particulates in the atmosphere will be picked up and register as they scatter light
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Old 02-11-2019, 06:27 PM
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In my humble opinion it is heat noise.
5 minute subs at 20 degrees is not a good combination.
Also your ISO will have something to do with this.

Leon
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Old 03-11-2019, 07:50 AM
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I’m with Leon. Looks a bit mangled but hard to tell with a compressed JPG. Post a crop of the affected area in full size png and one crop of a dark frame of 5m.
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Old 03-11-2019, 11:36 AM
Startrek (Martin)
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Ray and Leon
Looks like noise ( dark current ) as the stretched image had heavy horizontal banding
The only other time I experienced heavy banding this was when I captured the Rosette Nebula last year in summer with 5 minute subs
I didn’t take darks , just used some in my library which is not an accurate temperature match
So at this stage we will put it down to noise from the low QE of my Canon 600D
Won’t be back at my dark site for a while so can’t test 5 minute subs as I’m in Sydney now
Cheers
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Old 04-11-2019, 10:19 AM
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If you stretched your raw sub to the extreme I would expect the red to be even across the whole image if it was noise related, heat and light pollution related should be clearly a gradient on the shot. That would be my starting point to narrow it down, the jpegs dont help in this case.
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Old 04-11-2019, 11:06 AM
Startrek (Martin)
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As raw files are huge and I don’t have software to reduce the size to post , I took some photos of a raw image to show you the difference in pixels
Photo 1 (top)red affected raw image west side of meridian
Photo 2 red affected raw image on west side of meridian zoomed in area where red pixelation is bad
Photo 3 red affected raw image on west side of meridian zoomed in to corner of frame where red pixelation is not as evident or affected
Photo 4 (bottom) Unaffected raw sub on east side of meridian zoomed in
Hope this helps assess the issue ?
Cheers
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Old 05-11-2019, 10:10 AM
phomer (Paul)
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Martin,


Take a 5 minute exposure in the dark and it should all be sensor noise.


As the camera warms up it should gradually get worse.



Paul
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