Cause for rejection of frames

[Moonstruck]

I tried to use livestacking on the crab nebula and whirlpool galaxy last night with my C11 (with 0.7 reducer) and ZWO asi 2600 MC camera, and almost all the frames were rejected for both targets. I kept getting the error message "would not align." Any idea why alignment failed? On both targets the image was in focus. The stars looked good on the screen- round and bright, and the targets were visible. I have successfully used livestacking before many times with my C11 plus reducer and I am curious why it didn't work last night.

For some added info, there was a really bright (almost) full moon. Could that have contributed? Also, this is the first time I have used the asi 2600 for livestacking. I used a ZWO asi 294 MC successfully before to liveatack with this telescope. It seems strange that with a change to the 2600 it failed to align. Is the gain too high? (I had it around 400). Maybe the stars were bloated? Was the exposure (1-5 sec) too high? What are some common causes of failure of alignment and corrective actions I can take if it happens again?

Please let me know if there is any info I can send that would help diagnose the problem.

Thanks.

[admin]

Hi,

in that situation where you are getting alignment problems in live stacking, there are two things to check/try

1) Just reset the stack - perhaps the first frame added was bad somehow (blurred stars?) - that can make it hard for the subsequent frames to align no matter how good they look. By resetting you get a new first frame which might fix things

2) Look at the 'Alignment' tab in live stacking and check on how many stars are being detected in both the added frames and the stack so far. You may need to tinker with the star detection settings to get the number into a reasonable range (at least 10 to 15, probably no more than 100). You can also tick the box to highlight stars to make sure what is being detected is real stars, not noise, etc.

cheers,


Robin

[ChrisR Oz]

Do you have “optimise for faint stars” checked. I always need that selected, else have similar problems.
Cheers, Chris.

[Moonstruck]

Thanks for the feedback! I adjusted the star detection setting to 15 and also adjusted some of the other parameters, and was able to get an image without frames being rejected. Chris - next time I'll also be sure to check the "optimize for faint stars" box, so thanks for that.

However, I am having another problem. Due to the intense moon glow (brighter than I have ever imaged under before), once i got an image, the livestack was bright white, way over-exposed. I could barely see the target (M101) it was so bright. When I moved the white/mid/dark sliders, I was able to tone it down a bit and get the target to appear, but the sliders were so sensitive just a tiny bit of movement made it go from bright white to dark. I think I need to experiment with making fine adjustments to the histogram (as explained in your manual) such as pressing down the shift key while moving the sliders next time to get more range in the adjustments.

Other than that, do you have any suggestions on how to deal with bright moon glow when livestacking? Or is it a useless battle? I was reading from a poster in CN that the color noise control was useful for getting a better image. But it seems like that one reduces just color noise (as the name implies) and wouldn't do anything for moon glow.

Its strange, ever since I started using my new asi 2600 MC color camera I have been having problems livestacking. I used to use my 294 with C11 all the time for livestacking and got spectacular images almost all the time, with no issues with alignment, over exposure, etc. Is the 294 (bigger pixels, but less sensitivity) a better choice for this?

[admin]

Hi,

normally I'd say that the 2600MC (IMX571 sensor) is a camera that is head-and-shoulders above the IMX294 sensors, and I haven't had any problems with it - in fact I find it's remarkably reliable and easy to use for live stacking.

I suspect that there is some additional setting being applied here - either in the camera settings or elsewhere in SharpCap - that is brightening the image and causing the problems you are seeing. One possibility that comes to mind is that you have both the display stretch on the right and the live stacking stretch enabled by mistake - sometimes this can be useful with a weak display stretch to just tweak the output of live stacking a bit, but if you have a strong display stretch turned on then it is applied on top of the live stacking stretch and can cause the sort of excess sensitivity that you are seeing.

A good thing to try would be to close the camera and re-open with CTRL held down to clear any settings that are being restored from previous sessions -then re-set the settings that you need like RAW16, exposure, etc. and try again.

cheers,

Robin

[Moonstruck]

Thanks-I’ll make sure I’m not applying the display and stacking stretch at the same time. That could very well have been the cause as I use both often. I’ll also try clearing/re-entering the settings if it’s not an issue with stretching. I have to get this working the best I can since I’ll be using it for public outreach event soon! Thanks again.