Streaks in my image

Discussion of using SharpCap for Deep Sky Imaging
psy1280
Posts: 100
Joined: Wed Oct 24, 2018 4:52 pm

Streaks in my image

Post by psy1280 » Fri May 22, 2020 2:19 pm

I'm just getting acquainted to my Hyperstar and ZWO294 MC Pro. Last night I noticed a very faint streaking in the image. If anyone has any idea what's causing this and what I can do about it I would greatly appreciate the feedback.

Joe
Streaks3.jpg
Streaks3.jpg (426.99 KiB) Viewed 337 times

User avatar
turfpit
Posts: 1188
Joined: Mon Feb 13, 2017 8:13 pm
Location: UK
Contact:

Re: Streaks in my image

Post by turfpit » Fri May 22, 2020 2:57 pm

Joe

In order for anyone to have a chance at helping you, you need to post equipment (scope, camera, filters etc) & capture details including the capture settings file.

Dave;

psy1280
Posts: 100
Joined: Wed Oct 24, 2018 4:52 pm

Re: Streaks in my image

Post by psy1280 » Fri May 22, 2020 4:49 pm

Sorry for not including the following information:

I'm using a Celestron Evolution 8 SCT Alt/Az with Hyperstar and ZWO 294 MC Pro
Light Pollution Filter: IDAS LPS2


[ZWO ASI294MC Pro]
Debayer Preview=On
Pan=0
Tilt=0
Output Format=PNG files (*.png)
Binning=1
Capture Area=4144x2822
Colour Space=RAW8
High Speed Mode=Off
Turbo USB=80(Auto)
Flip=None
Frame Rate Limit=Maximum
Gain=350
Exposure=4
Timestamp Frames=Off
White Bal (B)=64
White Bal (R)=99
Brightness=10
Temperature=-14.8
Cooler Power=49
Target Temperature=-15
Cooler=On
Auto Exp Max Gain=285
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=C:\Users\Joe\Desktop\SharpCap Captures\2020-05-05\Capture\flats\21_40_53.png
Subtract Dark=None
#Black Point
Display Black Point=0.134765625
#MidTone Point
Display MidTone Point=0.319444606893424
#White Point
Display White Point=0.998046875
TimeStamp=2020-05-22T04:22:51.1541469Z
SharpCapVersion=3.2.6263.0
TotalExposure(s)=1928
StackedFrames=482

diant
Posts: 22
Joined: Tue Apr 28, 2020 8:35 am

Re: Streaks in my image

Post by diant » Fri May 22, 2020 5:01 pm

psy1280 wrote:
Fri May 22, 2020 4:49 pm
Subtract Dark=None
I suppose, this was the first cause. Were masterdark be applied, all things would be better.
And the second and the most important: You had a drift of field. And this factor may be used for profit.
Namely: You should return the field of view (return of aiming), but do it with some deliberate "accidental" error every time. This is called dithering. And "Drift Graph" tab may help in it very much.
Your streaks then will be eliminated in great degree.

User avatar
admin
Site Admin
Posts: 4327
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Streaks in my image

Post by admin » Fri May 22, 2020 6:08 pm

Hi,

Yes, subtracting a dark frame will help (make sure that it's captured at the same temperature to get best results) and the next stage pass that is to use dithering which will make small random movements of the mount between frames so that instead of getting streaks you get a much subtler pattern that is harder to notice.

Cheers, Robin

User avatar
oopfan
Posts: 665
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
Contact:

Re: Streaks in my image

Post by oopfan » Fri May 22, 2020 10:56 pm

I've taken plenty of fine astrophotographs without subtracting darks using a cooled camera. Joe's camera settings show that his sensor temperature was -14.8 degrees.

His settings file shows an exposure of 4 seconds, or is that 4 milliseconds? I would be very interested to know what his sky background ADU counts are. If you can show me that it is 10,000+ ADU then I say OK he needs to dither but if it is significantly less than that he should FIRST try increasing his exposure to 10 seconds. It never hurts to experiment before taking on another layer of complexity.

Brian

psy1280
Posts: 100
Joined: Wed Oct 24, 2018 4:52 pm

Re: Streaks in my image

Post by psy1280 » Sat May 23, 2020 4:06 pm

Brian,

I'm just beginning to get my hands around all this, but I believe the ADU for the ZWO294 is (read noise) 1.2e @35db gain. And yes, these were 2 second images.

I don't believe dithering is possible with my Alt/Az mount, but I may be mistaken.

Thanks for helping,
Joe

psy1280
Posts: 100
Joined: Wed Oct 24, 2018 4:52 pm

Re: Streaks in my image

Post by psy1280 » Sat May 23, 2020 4:07 pm

Oops! Sorry Brian, that was 4 second exposures

clouzot
Posts: 23
Joined: Thu Aug 08, 2019 11:13 am

Re: Streaks in my image

Post by clouzot » Sat May 23, 2020 5:16 pm

Some small remarks:
Gain=350
Which means you only have 9 stops of range, whereas most people will use gain 120 or 121 (close to unitary, and HGC mode enabled around this gain) that give you close to 13 stops. As the gain is much lower, Sharpcap may struggle to align on stars, so if you can use longer subexposures (I know, it's not easy with an Evo due to field rotation. I have the same mount) give it a try. The Evo should be good for 8-15s exposures with an Hyperstar (that what I use with my C9 +Evo + Hyperstar)
Colour Space=RAW8
You should also consider switching to RAW14 as you're loosing valuable dynamic range by restricting to 8 bits.

diant
Posts: 22
Joined: Tue Apr 28, 2020 8:35 am

Re: Streaks in my image

Post by diant » Sat May 23, 2020 6:13 pm

psy1280 wrote:
Sat May 23, 2020 4:06 pm
I don't believe dithering is possible with my Alt/Az mount, but I may be mistaken.
Very easy.
1). After beginning Live Stack, choose some bright star in the fields.
2). Switching Reticula ON (any type of it as you like)
3). Move Reticula crossline upon the chosen bright star. This crossline will work as the place of aiming.
4). Switch to the "Drift Graph" tab
5). Watching for the drift
6). When it reach some not very large value, press "Pause" (on the left side Live Stack's panel)
7). Switch "View" from "Stack" to "Individual Frame"
8). Now you can see (every 4 sec) the real position of your chosen star and can move it (by your synscan handset or from PC if mount connected to it). During this time Live Stack waits and skips all current frames. You can do all you want with handset...
9). You should return the star on the crossline... but you have to do some small "deliberate error" (it is the "dithering" trick).
10). Now you can release "Pause" button and continue to watch for the drift at "Drift Graph" tab
All things around such manipulations will quickly come to clear understanding.
For example: "deliberate error" better to do across a streaks on your image etc.

Post Reply