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What am I doing wrong?


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Did an imaging run on M101 last night, just a bit of practice- 30 X 30 second lights plus some darks and bias. ASI290MC on SW150P.

Came to do a bit of processing tonight and DSS keeps telling me only one of 26 images will be stacked. I've lowered the star detection to 2% and raised it to 97% but still no change.

An example of a light is shown below- I can't understand why it is so dark with only what seem to be hot pixels showing as the native image. Open it in GIMP and adjust the levels and some detail is revealed. 

I will also try an load a raw data file of one of the lights.

Light_ASIImg_30sec_Bin1_10.3C_gain0_2022-03-24_221230_frame0030.thumb.png.142357d5d971f4398059944d6dc3bf40.png

Light_ASIImg_30sec_Bin1_10.3C_gain0_2022-03-24_221230_frame0030.fit

Thanks for looking.

Matt

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As far as I'm aware the star detection threshold is only for aligning of frames by utilising a percentage of detected stars, it has no bearing on the resulting signal of the stack, I could be wrong.

Your image is extremely dark, it's darker than a dark sub, I did m101 the other day with 30 sec subs with a 224mc and you can see before editing slight hints of the galaxy, there's also a few stars surrounding it clear to see.

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I can actually see the galaxy in your sub, but DSS can only detect 1 star so can't align your stack. I don't know much about CMOS sensors, but you had the gain set to 0 which might be too low for 30s subs?

One solution is to process each linear sub individually to brighten it up and safe it to TIF before stacking.

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@Shibby- gain settings etc. are things I still need to get my head around.

My problem is I am a dinosaur and dislike on line manuals etc. with a passion. I much prefer having a hard copy manual in front of me whilst I set kit up. Look at manual, make adjustments on software as opposed to look at on line manual- switch to software screen- forget what I needed to adjust- return to on line manual- re-read instructions- switch to software screen- rinse and repeat 🙄

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As a general guide:

1. Most if not all CMOS cameras have a median type value of gain called unity, it's a good place to start. For my 183mm this is 111 on a scale from 0-300.

2. For full dynamic range (maximum number of distinct colour/grey values which can be defined based on the bit rate capability of the sensor electronics) you set the gain as close to zero as possible. By doing this the read noise (how much electronic noise is generated by the electronics per pixel) will be at its highest. The full well capacity (how many photons can hit a pixel before it gets fully saturated to white) will be at its highest potential. The images you will notice will appear dim like setting a DSLR camera to low iso.

3. For lower read noise you set the gain closer to maximum. The dynamic range will be reduced and so will the FWC. The images will appear bright like setting a DSLR iso on higher setting.

It's a balancing act between what you're imaging, your local light pollution levels and what you want the result to be like. There's no one rule and there is also a point of diminishing returns for each camera so you'd never set the gain within the final third/quarter of its gain range. Zwo include graphs for each camera on their website.

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