NOTE: Possibly solved! However still seeking some related/follow-up advice - Please see my update (1st April) further down the thread.
Hi, I'm seeking assistance to diagnose an image of M83 I recently took. The specific issue I'm having is a strong form of "smeared background noise"
I've tried multiple ways of stacking the data, both with darks/flat etc. to no avail. The attached image has a simple "medium curve" applied. No matter what I do to the initial stacking, the final result always contains a heavy background smear (the individual images appear fine)
Has anyone encountered this type of issue with a DSLR?
Image details:
20x300sec (guided, 8" LX200 ACF)
Canon 600D
ISO 800, shot in RAW
Stacked in Nebulosity 3
I've previously shot with higher ISOs (6400) and shorter subs so I've never encountered this specific issue before.
Thanks, Evan
Last edited by Cimitar; 01-04-2016 at 06:08 PM.
Reason: Minor title change & possible solution
I took this image of M83 back in March 2015. It's only 3 subs, at 120 sec each using ISO 6400, same camera. It also has a generic mid level curve applied to bring out the background noise.
In this image the background noise is random, no smear and no distinct pattern. Unfortunately I have to say at the moment that this final result looks significantly better than my most recent attempt using 5min subs at ISO 800.
This shouldn't be true... Hence the confusion
Cheers, Evan
Last edited by Cimitar; 19-03-2016 at 06:29 PM.
Reason: Spelling
Temperature, Read Noise, Interference ?
I've seen the smear before, unsure as to the exact cause.
In Photoshop 'Surface Blur' will mitigate some of the effect. NoiseWare will also fix it. Both will unfortunately lose some detail on the target although using Layers and masks in Photoshop you can get around that..
Your stock 600D is going to heat up during that 300" sub and heat will build up with each sub, affecting image quality. What settings do you have on the 600D? Are you using internal noise reduction, etc? Personally I turn all that stuff off. What do your bias frames and darks look like? How does a bias frame compare to your dark - the answer may lie there.
Temperature, Read Noise, Interference ?
I've seen the smear before, unsure as to the exact cause.
In Photoshop 'Surface Blur' will mitigate some of the effect. NoiseWare will also fix it. Both will unfortunately lose some detail on the target although using Layers and masks in Photoshop you can get around that..
Thanks Brent , I have NEAT Image noise reduction software and I was going to try PS, so I'll see what I can do with layers etc. The atmosphere was quite dense with humidity that night, so it'll be interesting to see if my other images also have the smear.
Quote:
Originally Posted by glend
Your stock 600D is going to heat up during that 300" sub and heat will build up with each sub, affecting image quality. What settings do you have on the 600D? Are you using internal noise reduction, etc? Personally I turn all that stuff off. What do your bias frames and darks look like? How does a bias frame compare to your dark - the answer may lie there.
Cheers Glen , I have the built-in noise reduction switched off and was using darks & flats. I was playing with my RA PEC for the first time that night and did some training, followed up by multiple updating sessions. Not sure if that would have any affect/contribute to the tracking/smearing issue. I didn't take any bias frames as I thought the darks may have that element covered, however I'll go back and takes some bias frames and investigate the difference.
Quote:
Originally Posted by blink138
it is a hot sensor
pat
Thanks Pat, it occurred to me after reading all of your comments that this is the first time I've taken 15+ subs with such a long duration. In the past it has typically been much less. I'll investigate the heat issue some more and do some trials in the backyard.
I have seen such streaks several times with my 1200D with much shorter exposures. Never before with Nikon (not sure if it means anything). Changing stacking parameters fixed the problem for me every time though.
Try stacking only the first few images, i.e. before the sensor got hot.
If your game, the 600D can have the sensor cooled to 0C. Together with a full spectrum filter mod you could have an excellent astro camera. Just have a look at rchesire's great thread on cooling dslrs in the DIY forum herel
If your game, the 600D can have the sensor cooled to 0C. Together with a full spectrum filter mod you could have an excellent astro camera. Just have a look at rchesire's great thread on cooling dslrs in the DIY forum herel
Heheheh, Leading them to the Dark Cooled Side are you Glen ?
My Pentax *ist DS is capable of producing streaky images. I did a stack of 15 images of Comet Lemmon a while back and ran it through DSS. No idea what caused the streaky background. All attempts to find a solution proved fruitless. No-one I talked to seemed to be able to offer any solutions. http://www.iceinspace.com.au/forum/s...d.php?t=103394
I have seen such streaks several times with my 1200D with much shorter exposures. Never before with Nikon (not sure if it means anything). Changing stacking parameters fixed the problem for me every time though.
Try stacking only the first few images, i.e. before the sensor got hot.
Thanks Luka , at first I thought it must have been my stacking method, however after removing the darks & flats and taking a generic approach the artefact still appears to remain embedded in the image. I did try stacking some other images from the night and they appear ok so far (which is adding to the confusion), but I haven't gone back to try only the first 5 images from the problem target. Hopefully I may find the issue lying hidden there somewhere...
If your game, the 600D can have the sensor cooled to 0C. Together with a full spectrum filter mod you could have an excellent astro camera. Just have a look at rchesire's great thread on cooling dslrs in the DIY forum herel
Quote:
Originally Posted by sil
I get the same on my Nikon D800e too.
Quote:
Originally Posted by ZeroID
Heheheh, Leading them to the Dark Cooled Side are you Glen ?
Haha, ... oh how I dream of making a cooler box for my DSLR. It's the only camera I have though and I sometimes have nightmares about breaking it with a cold-finger mod or drowning it in a sea of ice/condensation
My Pentax *ist DS is capable of producing streaky images. I did a stack of 15 images of Comet Lemmon a while back and ran it through DSS. No idea what caused the streaky background. All attempts to find a solution proved fruitless. No-one I talked to seemed to be able to offer any solutions. http://www.iceinspace.com.au/forum/s...d.php?t=103394
Hi Mike, wow - bang on the money there. Your image is exactly the same as mine The smearing effect is very evident! The confusing thing for me is the fact that there is a distinct pattern to it, it's almost as if the background noise is tracing out the same star-trail pattern when you take a long exposure and see stars rotating around the SCP.
The problem is then compounded by the fact that the stars and DSO are all tight/compact objects with no obvious rotation
Were you ever able to replicate the result? I could just bin the images I took on the night, but it seems such a waste of 2+ hours of data on M83.
One thing I do remember doing differently that night was I changed my DSLR colour balance from daylight to fluorescent. I don't see how that would make any difference though.
Hi Mike, wow - bang on the money there. Your image is exactly the same as mine
Were you ever able to replicate the result?
Yes, I have wide fields of the LMC complete with streaky backgrounds.
Quote:
Originally Posted by Cimitar
One thing I do remember doing differently that night was I changed my DSLR colour balance from daylight to fluorescent. I don't see how that would make any difference though.
If you shoot RAW, it will make no difference at all. All my backgrounds that are streaky were all shot with the camera on a static tripod. I suspect that DSS cannot handle the field rotation at short focal lengths. My examples are all shot at 18mm.
What about looking at the problem through the other end of the telescope, [sort of pun intended]. I've never seen streaks anything like those, so am I doing anything differently to you guys that do get them.
Being an old gas emitter, I am stuck for evermore at the newbie level
as far as the digital side of things is concerned.
I use inbuilt high ISO noise reduction and long exposure noise reduction.
No separate darks, flats, or biases.
I mostly use the camera's own battery for runs of subs[ say 50-60
of 30-90 secs], using my 240v adaptor only for longer runs than that.
I don't normally guide, just manually very occasionally.
I very rarely have a computer connected to my rig.
I either put subs into DSS of equal duration and ISO, or more often, a
mix of both duration and ISO.
I always use daylight colour balance.
I focus before the run using Live view, and only use the LCD screen
about every 20 or so subs, to recheck the focus/ tracking.
I use the default settings in DSS.
I don't know if any of that might contain a clue or two.
raymo
Yay! After much diagnosing I think I may have finally cracked this nut (See attached files).
The first image is of 4 clean images (i.e. minimal trailing) from the night. These were taken early on in the piece, circa 12am - all fine, no smears.
The next 3 images are clean and were taken later in the evening, circa 1.45am - again fine, no smears.
The third image is what happens when I stack all 7 together - notice the smearing starting to appear in the background! Note - During the session i actually took 25 subs, however I've only used the best 7 to minimise any other potential issues.
The fourth image is a GIF of the field rotation that's occurring. Normally this wouldn't bother the stacking, however when you look closely at the gif, you can see the background slowly beginning to smear.
1) Now... I only took 7 darks during the night. I didn't start taking the darks until 4.40am. Somehow I think this is a major contributing factor? (each sub was 300sec at ISO 800)
2) Something that's also bothering me is the field rotation. It appears to be happening around the SCP or something else out towards the upper left frame... not the DSO. So, my question is this - does field rotation (if poorly polar aligned) occur around the DSO, or will it cause the movement I'm seeing in my image?
As always, thanks in advance.
PS. Hoping to get to the bottom of this as it may also assist other beginners in the future
, I have NEAT Image noise reduction software and I was going to try PS, so I'll see what I can do with layers etc. The atmosphere was quite dense with humidity that night, so it'll be interesting to see if my other images also have the smear. 
... oh how I dream of making a cooler box for my DSLR. It's the only camera I have though and I sometimes have nightmares about breaking it with a cold-finger mod or drowning it in a sea of ice/condensation 
