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INDI Library v1.8.0 is Released (27 Jul 2019)

INDI Library v1.8.0 is mostly a maintenance release to fix a few bugs in several drivers.

Excellent tutorial on minimizing noise and optimizing exposure parameters

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Replied by El Corazon on topic Excellent tutorial on minimizing noise and optimizing exposure parameters

fenriques wrote:

El Corazon wrote: Here is another informative (and at times spirited) discussion on the same topic. That one also addresses the effect of gain.

www.cloudynights.com/topic/573886-sub-ex...00-and-maybe-qhy163/

Thanks, I read the thread (well ,not all 188 posts...), argumentations are solid but the data presented are mainly empirical. There's another useful thread on CN that discuss the theory behind the calculations:
www.cloudynights.com/topic/536809-conver...o-photon-flux/page-2 (#38)

Do you have an excel file with simulations of suggested exposure times to share? I would like to compare to mine



Hi Fenriques,

Sadly, no, don't have an Excel file with simulations. That might be useful to build.

I only have the numbers I gave in my last reply, which fit the abhorrent conditions in my backyard in a white zone and which match closely what the sharpcap site says and what the formulas in the cloudynights blog also suggest. They were obtained recently with an RC-8" at f/8 using the ASI1600MM Pro at 240 gain. The ADUs come out a little higher than in the cloudnights discussion I provided the link to, I will continue tweaking times and gain some more until my results are optimized to the conditions (that doesn't say much!).

One drawback not discussed in the video presentations or the blogs is the time factor required for downloading and dithering. The shorter the exposure times, the more those come into play. By going to shorter exposure times one will progressively end up with less integration time, since progressively more time is being wasted downloading the images and dithering. That is especially critical when using a Raspberry Pi, which is much slower than a mini-PC, or when downloading the images over WiFi. Here, it becomes essential to use a mini-PC at least, preferably the more computing power one has the better. Also, USB3 becomes absolutely critical for downloading the images. For those reasons, it seems to me to make sense not to go below 30 s exposures and rather preserve dynamic range by using a lower gain for luminance, while keeping the median ADUs in the low 2000s.

That makes the scheduler more important than ever. With that, one can then program image acquisition at different gain values, i.e. perhaps 120 gain/30s for L, 180 gain/30s for RGB and 300 gain/60s for narrowband from the city at f/8.

Jasem, if you are reading this, that would be a useful addition to the capture module: Allow different gain values to be programmed for the different filter settings (rather than only one gain value for the entire sequence), without the need to set up separate entries for the same target in the scheduler.

What do y'all think?

Best

Jo
Atlas Pro AZ-EQ, ASI1600MM-Pro, ASI120MM-S, ES102ED, WO-Z61, Nikon D3300, ASI-EFW, ZWO LRGB,Ha,O3,S2 filter set
4 months 3 weeks ago #36935

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Replied by fenriques on topic Excellent tutorial on minimizing noise and optimizing exposure parameters

hi Jo,
I'm using a color cmos so I'm not really concerned about the gain issue you mentioned.
Anyway, having a different gain setting per sequence wouldn't increase time to take calibration frames too much? that could be automated of course but storage / download time would increase.

Ferrante
4 months 3 weeks ago #36967

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Replied by El Corazon on topic Excellent tutorial on minimizing noise and optimizing exposure parameters

fenriques wrote: hi Jo,
I'm using a color cmos so I'm not really concerned about the gain issue you mentioned.
Anyway, having a different gain setting per sequence wouldn't increase time to take calibration frames too much? that could be automated of course but storage / download time would increase.

Ferrante


Hi Ferrante,

Don't tell anyone (:blush: ) and don't post that fact on the internet, but I am a little lazy with my calibration frames. I am reusing my darks and flats for pretty extended periods of time and given that my area is light polluted, I have no problem with that. The noise is always much greater than the subtle difference from sensor shift over time. I have to use narrowband, one shot color is just not cutting it from the city, except for the very brightest objects like M42.
Anyway, given the dead time lost in downloads and dithering, exposure times of less than 30s seem to be counterproductive as they cut down substantially on total integration time achieved during the session. That was the main point I wanted to draw attention to.
Cheers
Jo
Atlas Pro AZ-EQ, ASI1600MM-Pro, ASI120MM-S, ES102ED, WO-Z61, Nikon D3300, ASI-EFW, ZWO LRGB,Ha,O3,S2 filter set
4 months 3 weeks ago #36971

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