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First light on Iris Nebula 42 minutes with my new ASI071


gorann

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Finally we have some astrodarkness up here, almost three hours of it. So on Friday night I could test my new ASI071 MC pro (a cooled APS-C sized OSC). First hour went into polar aligning and star aligning the EQ8 on the pier (it has been stored inside over the summer). Earlier in the afternoon I had managed to get rid of most of the backlash by finally being brave enough to fiddle with the Dec gear. So then I had a bit less than two hours remaining for imaging. I hooked the camera onto my Esprit 150 and set it on gain 90 (unity gain), offset to 20, and chip temp on -15°C. I started with an hour of 2 min exposures and then 1 min exposures. In the morning I found that the first images looked quite bad and realized I must have had dew on the camera window. I had missed to tick the anti dew box in the ASICAP programme. Fortunately, the dew spontaneously went away after about an hour so I ended up with 9 x 2 min + 24 x 1 min = 42 min of imaging. I think it looks promising enough. Very little noise in this camera. I did do darks but they were very clean and probably not needed.

Earlier in the day I had also figured out that my Dell Windows 7 computer could not handle PHD2 (with a QHY5LII) and ASICAP for the camera at the same time. I think it was the PHD2 (or the QHY) that messed it up or some USB crash. So I ended up running the ASI071 on my Mac Powerbook.

I feel that I learned a lot even if I did not get great deep data. The EQ8 did rather well especially since it was essentially pointing the scope straight up, with RA and RSM between 0.5 and 0.8". Next time I will tick the anti-dew box and image for longer, maybe with a bit longer subs.

Any comments most welcome especially regarding settings and exposure times for this camera.

IrisNeb ASI071 0139-0222 PS24smallSign.jpg

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Congrats on your new CCD and a very promising first lights!

I still need a few more clear nights to sort out my gear after 2 years of almost no use, but it's very nice with astro darkness slowly returning to our altitudes.

/Patrik

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On 27/08/2018 at 13:53, poogle said:

Congrats on your new CCD and a very promising first lights!

I still need a few more clear nights to sort out my gear after 2 years of almost no use, but it's very nice with astro darkness slowly returning to our altitudes.

/Patrik

Thanks Patrik!

I know the stressful feeling of getting the gear and procedures sorted, including finding everything, even after just a summer break in imaging. I have to say that the ASI camera with the ASICAP programe was very much plug and play. My main problem was that the stupid Windows laptop I am forced to use with the QHY guiding camera (QHY has still not made a Mac driver) refused to also run ASICAP at the same time so I hade to run two laptops, using my trusted Mac for the ASICAP. Need to solve that since I like to retreat indoors while imaging and use my Mac for other tings.

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Nice to get everything working on a first light and to iron out the mistakes. Great that you managed to get an image from such limited data.

I like gain 50 as it's a good trade off between dynamic range and low read noise. I've found 150 seconds to be my limit for the gear and location. Looking forward to seeing more with the new camera best of luck.

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34 minutes ago, Allinthehead said:

Nice to get everything working on a first light and to iron out the mistakes. Great that you managed to get an image from such limited data.

I like gain 50 as it's a good trade off between dynamic range and low read noise. I've found 150 seconds to be my limit for the gear and location. Looking forward to seeing more with the new camera best of luck.

Thanks for the suggestions! Do you know if the gains comparable between ASI 071 and 1600? On ASI 071 unity gain is 90.

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The sensors are different brands.

ASI 1600 has unity gain at 139.

It would make more sense to refer to gain in e/adu, with unity gain being 1 e/adu. This is the only way to compare gain of different cameras, and as a reference for exposure time.

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10 hours ago, gorann said:

Thanks for the suggestions! Do you know if the gains comparable between ASI 071 and 1600? On ASI 071 unity gain is 90.

No the two sensors are not comparable with regards to gain. I use gain 50 with the 071 and gain 0 on the 1600 when shooting broadband as the 1600 saturates too easily. I was using gain 0 with the 071 for highest dynamic range but i found gain 50 to be a nice reduction in read noise while sacrificing very little in the way of dynamic range.

zwo_asi071mc-cool_read-noise.thumb.jpg.b9234a7653038a62c45c7afdd8aaec41.jpg

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12 hours ago, wimvb said:

The sensors are different brands.

ASI 1600 has unity gain at 139.

It would make more sense to refer to gain in e/adu, with unity gain being 1 e/adu. This is the only way to compare gain of different cameras, and as a reference for exposure time.

 

3 hours ago, Allinthehead said:

No the two sensors are not comparable with regards to gain. I use gain 50 with the 071 and gain 0 on the 1600 when shooting broadband as the 1600 saturates too easily. I was using gain 0 with the 071 for highest dynamic range but i found gain 50 to be a nice reduction in read noise while sacrificing very little in the way of dynamic range.

zwo_asi071mc-cool_read-noise.thumb.jpg.b9234a7653038a62c45c7afdd8aaec41.jpg

If I read these curves right, it would be an advatatge to set a high gain if there are no really bright stars or objects in the image since I then do not need a big full well capacity. Having a high gain gives med more ADUs per photon so I can see fainter stuff and I also get less read noise. And I could take shorter and more exposures with a high gain. Are these interpretations correct? If that is the case, then the only reason for not using a very high gain is the presence of bright objects (but that could be handles by adding a series of short exposures).

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1 hour ago, gorann said:

 

If I read these curves right, it would be an advatatge to set a high gain if there are no really bright stars or objects in the image since I then do not need a big full well capacity. Having a high gain gives med more ADUs per photon so I can see fainter stuff and I also get less read noise. And I could take shorter and more exposures with a high gain. Are these interpretations correct? If that is the case, then the only reason for not using a very high gain is the presence of bright objects (but that could be handles by adding a series of short exposures).

Yes but your dynamic range suffers. I suppose there's always a trade off. I've never tried really short exposures so experiment might be the way to go. Having said that i got tired of short exposures with the 1600 due to massive amounts of data and longer stacking times. Sometimes hours to create a stack.

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Somewhere on the ZWO site (forum, I believe), someone made a comparison between fewer long subs at low gain, and more short subs at higher gain. The endresult was quite similar. While each sub has a lower dynamic range (bit depth), the large number of subs leads to an increase in dynamic range, without losing SNR.

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15 hours ago, wimvb said:

Somewhere on the ZWO site (forum, I believe), someone made a comparison between fewer long subs at low gain, and more short subs at higher gain. The endresult was quite similar. While each sub has a lower dynamic range (bit depth), the large number of subs leads to an increase in dynamic range, without losing SNR.

So then low gain and few subs would be to prefer to save time on stacking and harddrive space...... I wonder if guiding error should come into the equation somehow?

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There are several factors at play:

Noise reduction, depending on total integration time.

Dynamic range, depending on gain.

Bit depth recovery, depending on number of subs.

These factors affect each other, and are affected by local conditions (gear and sky). I'm sure there is a theory behind all this, but it's easier and safer to just experiment. Personally, I prefer lower gain, longer exposures and more dynamic range.

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4 hours ago, wimvb said:

This may be of interest:

https://astronomy-imaging-camera.com/tutorials/cooled-asi-camera-setting-in-ascom-driver.html

Not sure if this was the article I had in mind, but interesting anyway.

 

4 hours ago, wimvb said:

There are several factors at play:

Noise reduction, depending on total integration time.

Dynamic range, depending on gain.

Bit depth recovery, depending on number of subs.

These factors affect each other, and are affected by local conditions (gear and sky). I'm sure there is a theory behind all this, but it's easier and safer to just experiment. Personally, I prefer lower gain, longer exposures and more dynamic range.

Interesting Wim and I get the feeling that we are all a bit confused and that the new CMOS cameras give more adjustments to play with than are good for us. I assume I will stick to the middle ground to start with (around unity gain) to play it safe (set the camera to a "lagom" level as we say in Swedish). Total integration time is probably still the king.

Still, what do you think about guiding. Would poor guiding be less important with many short subs?

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The ZWO CMOS cameras are certainly a whole new area to get to grips with.  

I am a newby but the low noise of the cooled ZWO cameras completely changes the game. 

Unity gain is fine for me. I haven't tried it on a relatively bright target yet so not sure thats the only answer.  

Good guiding is always going to be important regardless of the camera if you are doing long exposures.

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8 hours ago, gorann said:

Still, what do you think about guiding. Would poor guiding be less important with many short subs?

On occasions when I can't get guiding to work, I resort to short exposures at high gain. That way I don't lose a good night.

There is a wide variety between ASI cameras. My ASI174MM-COOL has considerably higher read noise than yours. Some have 14 bit, pixel size varies widely, and the ASI1600 has an entirely different sensor. That's why it's important to experiment, and create one's own method of operation.

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