Not able to stack frames

[Moonstruck]

Hi,
I tried to image the sombrero galaxy a couple nights ago but couldn't stack my frames. The stars in each frame were extremely dim and barely visible. Deep sky stacker gave me a message saying that only one frame could be stacked since not enough stars were present. I had the gain set to 100 (unity gain) on my asi2600 camera as usual, and the exposure was set to 120 sec. I took around 40 frames. I was using a C11 w/0.7 reducer and EQ6 mount.

Any idea what the issue could be? Here is a link to one frame, and my camera details. All frames were about the same dimness.

https://drive.google.com/file/d/1P4UhEv ... sp=sharing

[ZWO ASI2600MC Pro]
CameraSerialNumber=08224A0C16020900
FrameType=Light
Debayer Preview=On
Pan=0
Tilt=0
Output Format=FITS files (*.fits)
Binning=1
Capture Area=6248x4176
Colour Space=RAW16
Exposure/Gain Shift=0
Hardware Binning=Off
High Speed Mode=On
Turbo USB=100
Flip=None
Frame Rate Limit=Maximum
Gain=100
Exposure=120.000s
Timestamp Frames=Off
White Bal (B)=50
White Bal (R)=50
Brightness=50
Window Heater Power=On
Cooler Power=72
Temperature=-10
Target Temperature=-10
Cooler=On
Auto Exp Max Gain=337
Auto Exp Max Exp MS=30000
Auto Exp Target Brightness=100
Mono Bin=Off
CA Reduction/Synthetic Blue=Off
Mask over exposed pixels=Off
Flip (after dark/flat)=None
Trail Width=3
Minimum Trail Length=100
Trail Detection Sensitivity=9
Remove Satellite Trails=Off
Background Subtraction=Off
Planet/Disk Stabilization=Off
Banding Threshold=10
Banding Suppression=0
Apply Flat=None
Dark Scaling (Experimental)=Off
Hot Pixel Sensitivity=5
Subtract Dark=None
DisplayStretchEnable=1
NegativeDisplay=0
Display Black Point=0
Display MidTone Point=0.06097560975609756
Display White Point=1
Notes=
EQMOD ASCOM HEQ5/6=RA=12:41:29.4,Dec=-11:47:19 (JNOW)
TimeStamp=2026-05-19T01:57:31.2504466Z
SharpCapVersion=4.1.14136.0
StartCapture=2026-05-19T01:57:09.5147609Z
MidCapture=2026-05-19T05:37:41.0840654Z
EndCapture=2026-05-19T09:18:12.6533700Z
JDStartCapture=2461179.581360
JDMidCapture=2461179.734503
JDEndCapture=2461179.887646
Duration=26463.139s
FrameCount=220
ActualFrameRate=0.0083fps
TimeZone=-4.00

[admin]

Hi,

interestingly I don't see a problem with live stacking with that image - I loaded it up into 'Test Camera 1' which just repeats it over and over and live stacking was quite happy detecting 30+ stars in the image and calculating an alignment.

If you look back on the log file from the imaging session, it may give some indication of why the image was failing to stack - some things to check are

* using an FWHM filter in live stacking in SharpCap - the FWHM of the image is 13 pixels or so, so a filter setting from a previous session with a different setup might exclude all the frames

* Star detection settings in live stacking - possibly with different settings not enough stars would be detected. I have the 'optimize for faint stars' option turned on in the star detection, which isn't part of the defaults - worth trying that (although ~10 stars were still detected - enough to align - without it).

cheers,

Robin

[Moonstruck]

Thanks. How do I get a log file from the session?

Also- I didn’t think I set to livestack… but did I? I thought I set it for regular capture, but maybe not.

[admin]

Hi,

ah, OK, I was thinking that you had been struggling to stack the files in SharpCap Live Stacking and then tried DSS as a test to see if that worked... My mistake.

Based on my test with SharpCap, and loading the image you shared into DSS just now, I think there are enough stars findable to stack, so I would check a couple of things in DSS...

* Firstly, is your DSS up to date - looks like the latest is 6.2.0 and there have been lots of improvements recently thanks to Dave (@perdrix).

* Secondly, check the star detection settings in DSS - they are in the advanced tab on the 'Register' window - maybe increasing the sensitivity will help. I found I got 66 stars with it set to 'auto'.

cheers,

Robin

[Moonstruck]

Thanks very much! I uploaded the new version of DSS (6.2.0) and it did the trick!

[cyrille.de.brebisson]

Hello,

I to am having issues with images not stacking in live stack mode.
I am imaging using a long focal scope (4800mm) and the stars are quite large on the sensor, which I am assuming is part of the problem.

2 images can be found here if it helps: https://drive.google.com/file/d/1CmixDu ... drive_link

Can you help me figure out which settings I need to change to make stacking work properly?

Thanks,
Cyrille

[admin]

Hi Cyrille,

for now, I'd suggest setting the 'Maximum Star Size' higher in the 'Alignment' tab of the live stacking area. Setting this up to 100 allows the detection to pick up the brighter stars in the image (which are otherwise too big and being ignored). Once the bright stars are picked up, the alignment seems to work.

I will look into this a bit more though - there's no real reason why a good selection of fainter stars shouldn't work for alignment too... At least, I don't think there should be one!

cheers,

Robin

[admin]

Hi,

just to update - I tracked down the cause of this latest report from Cyrille...

It turns out that some really ancient code in the live stacking star detection was converting the latest frame from the camera to 8 bit before doing star detection on it. On the other hand, the star detection on the stars already in the stack was being done in 16 bit. This, along with the exclusion of the biggest stars due to them being above the default 50 pixel width meant that the stars being detected in the stack and the frame weren't similar enough to align (the alignment uses the brightest 15/20/25 stars in each, but those were not always the same stars between the new frame and the stack).

Once upon a time this code was essential - star detection only worked on 8 bit images in the early days of SharpCap. Then it didn't matter - for a long time the star detection did work on 16 bit images but gave very similar results to the 8 bit version of the image. Then, a few months back I did some changes that drastically improved star detection on 16 bit images and suddenly this old bit of code that has done no harm for more than a decade is a hidden bug

Anyway, I have resolved the problem and that will be in the next update of SharpCap 4.2 beta.

cheers,

Robin

[cyrille.de.brebisson]

It worked! thanks.