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NGC 7822 Red


Rodd

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I am still trying to get a handle on the asi 1600's method of imaging for broadband.  Spoiler alert:  DO NOT VIEW AT FULL RESOLUTION (or limit such viewing to the brightest areas).  I am struggling with exposure times.  I find that due to download times and "wait" times (what ever that is), coupled with dither delay times, plus adding 10 min or so for refocusing, the collection of 1 hour of data using 30sec exposures takes almost 2 hours.  So, what ever time benefit I gain by shooting at F3 over F5.4, I loose due to the infernal delays.  I have my dither delay set at a bare minimum 10 sec.  I have not been able to determine what the "waiting" delay is for--download perhaps?  15-20 sec seems exorbitant for download.  Any way, this image consists of 100 30sec Red subs and 30 60sec Red subs (conditions were too poor for Lum).  I am seriously considering going to 2min.  Much longer than that and we get into "what is the benefit of F3 territory".  On the other hand, the longer the subs, the less a 20 sec delay between subs adds to the total imaging time.  So this image contains 1 hour and 20 minutes of data.  Conditions were deplorable in general, with a moderately clear zenith, which is where most of this data came from.  

Bottom line...80min should be enough to render a smooth, low noise Red stack .  The total integration times between the STT-8300 and the ASI 1600  are typically said  be comparable--the 8300 requiring less subs of longer duration and the asi 1600 requiring more subs of shorter duration.   Combine this with shooting at F3, and I expected the total integration time of a stack to be 30-40 min.  Maybe an hour.  This is far from the reality I have seen.  For bright areas it seems to be closer to truth, especially during pristine conditions (ie M8/M20, M31).  But if I am ever goin to attempt the IFN, I need to dial it in better. So far, all attempts have been at unity gain.  Offset no longer variable.

integration.thumb.jpg.db7db36aa470360ffe8dd804108fbfcb.jpg

 

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Nice monochrome. It will be interesting to see the colour version.

I think the total integration time depends more on local sky conditions than difference in gear. Imaging from a light polluted site will require more total time on target. I recently saw an article by Jerry Lodriguss (thanks, @Firas) arguing that for every unit decrease in magnitude, you need to image 2.5 times as long, to compensate for the added noise of the light pollution. Someone with magnitude 20 sky will need to image 2.5 hours for each hour with mag 21 sky, and with mag 19 sky, 6.25 hours. Faster optics don't just collect more target photons; they also collect more light pollution photons.

For my imaging sessions with the ASI and guiding, I found that dithering ate a lot of imaging time. I don't always use it, even though I should.

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6 hours ago, wimvb said:

Nice monochrome. It will be interesting to see the colour version.

I think the total integration time depends more on local sky conditions than difference in gear. Imaging from a light polluted site will require more total time on target. I recently saw an article by Jerry Lodriguss (thanks, @Firas) arguing that for every unit decrease in magnitude, you need to image 2.5 times as long, to compensate for the added noise of the light pollution. Someone with magnitude 20 sky will need to image 2.5 hours for each hour with mag 21 sky, and with mag 19 sky, 6.25 hours. Faster optics don't just collect more target photons; they also collect more light pollution photons.

For my imaging sessions with the ASI and guiding, I found that dithering ate a lot of imaging time. I don't always use it, even though I should.

That explains allot.  Dim target and bad conditions, translates to allot of time. Yes dithering eats time -especially when subs are short.  In Maxim there is no way to dither every 3rd frame, or every fifth frame, or what ever--unless you get the really expensive software that controls everything (CCD commader?  something like that.  I understand that PHD can dither every other frame--or whatever frequency you want.  That would help.

Rodd

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I don't think I'd have the patience to dither every frame with only 30 s exposure time. I use the linux software INDI with Kstars running on my windows computer. INDI is installed on a Raspberry Pi, and is near my scope, while Kstars controls it from indoors. INDI/Kstars allows dithering any x frames, either with phd or its internal guiding software. Best of all, it's free. It does require a basic knowledge of linux, but very much "learn as you go". (There's also a pre-installed commercial version called stellarmate.)

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3 hours ago, Rodd said:

That explains allot.  Dim target and bad conditions, translates to allot of time. Yes dithering eats time -especially when subs are short.  In Maxim there is no way to dither every 3rd frame, or every fifth frame, or what ever--unless you get the really expensive software that controls everything (CCD commader?  something like that.  I understand that PHD can dither every other frame--or whatever frequency you want.  That would help.

SGP will do that as well, as indeed with APT (which is free) - FWIW, PHD doesn't control when to dither - the client software that connects to PHD has to tell it when to do the dithering. 

 

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I use APT and this allow dithering a different frames and is a great bit of kit. With regards to image download are you using usb 3 or 2 and what speed have you set for usb?. I seem to have similar issue when taking a single shoots it can just hang and needs cancelling, after a few attempts its all okay. I do get the feeling that these cameras may be a bit sensitive with usb connections and for some reason my startek usb 3 hub only seems to runs it on usb 2.

Make sure the usb speed is down to 40, if you are running a hub try a direct connection and possibly another usb lead.

 

Mark.

 

ps I would not expect too much detail from rgb as this will come from the L or Ha. If you use bias frames try it without and just have your darks, flats and dark flats.

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7 hours ago, spillage said:

Make sure the usb speed is down to 40, if you are running a hub try a direct connection and possibly another usb lead.

How do you set this?  There is not a setting in Maxim.  

Rodd

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You should be able to do this via the zwo settings. In apt you click on the camera tab then click settings, this opens up the zwo program enabling you the adjust gain, offset and usb speed. Sorry have not used maxim so maybe some here can help.

 

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3 hours ago, spillage said:

You should be able to do this via the zwo settings. In apt you click on the camera tab then click settings, this opens up the zwo program enabling you the adjust gain, offset and usb speed. Sorry have not used maxim so maybe some here can help.

 

They changed the camera--offset is no longer variable--the only thing I can change is Gain.  There is not a option for USB setting either.  Maybe in sharpcap or one of the other planetary platforms.

Rodd

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3 minutes ago, spillage said:

I knew about the offset change but did not realize the usb speed change. Mine is as below. Although pulling my hair out trying to get it to connect via usb 3.0.

 

I have never used the ZWO interface.  I use Maxim for capture and the available camera controls are limited.  If I open another platform (ZWO) and change settings, will they carry over to Maxim?  I am not even sure how to open the ZWO interface.

Rodd

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