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Jon you are never using the setting 0/10 for long exposures? I can do my shooting under a 20.8 mag/arsec sky (Unhidron SQM) and I am only using the 0/10 setting for exposures from 300-600 sek. Should I use the 75/15 setting? I have opted not to use the lowest gain setting. You actually do not really gain any dynamic range (because of the 12-bit ADC, 12 stops is the effective max), however read noise AND quantization noise increase. On top of that, the amp glows increase with time just like dark current, only at a different rate. Beyond 600 seconds they become problematic, beyond 900 seconds they become quite severe. At low gain, especially under dark skies, the amp glows can become very problematic when imaging at Gain 0. My personal recommendation is to stick to Gain 75 as the lowest gain setting. You will benefit from the maximum DR the camera can offer (12 stops), lower read noise than gain 0 (~2e- RMS), lower quantization error, better gain, etc. Gain 75 is better all around, IMO. Depending on where you are, you may only be able to get 20 second L exposures (like me, f/4 in a red/white zone), or you may be able to get 120 second L exposures (a slower scope, or at a dark site, etc.) With both a slow scope and a dark site, you should be able to get even longer exposures. Something else to keep in mind. More subs is not bad. Actually, up to a point, more subs is quite beneficial, especially for this camera. Stacking increases bit depth and dynamic range. The more you stack, the more bits you recover and the more dynamic range you have. I highly recommend discarding old patterns, such as 1200 second or longer exposures...for any reason (with high gain on this camera, you can use as little as 45 second subs for NARROW BAND!!) Long exposures WERE only necessary in the past because of high read noise. At higher gain settings, this camera has 2e- read noise or less, and as low as ~1.1e- at Gain 300. You simply do not need long exposures. Stacking more subs, especially dithered subs, has many benefits with this camera (and with most cameras, really). Sigma clipping or linear fit clipping work better with more subs. Drizzling, which is a way to increase resolution and detail when integrating dithered subs, works better when you integrate LOTS of subs. And of course there are the bit depth and DR gains mentioned before. I generally recommend that people get 60-80 subs with this camera, at least. Personally, I've stacked up to 200-300 with shorter exposure higher gain images. Even at gain 75, which I use for very faint objects, I try to stack at least 80 subs. Stacking more subs can mean more "costs"...you need more disk space, more processing time. But in the long run, I do believe there are distinct benefits. |
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David Dvali:Jon Rista:Jon, isn't the Gain 50 with FW capacity > 10k e and a RN 2.5e would give you more CCD like performance? Why did you choose 75? Yes, the main reason is the 12-bit ADC. Lower than Gain 75, and you actually start losing more. You can't really get more than 12 stops of DR (there may be some caveats there, but in general, 12 stops is what you get), and read noise keeps increasing as you go to lower and lower gain settings. The other reason is the read noise is actually quite low at 2e- @ Gain 75. I have found that i can properly swamp read noise at Gain 75 with as little as 600 second exposures @f/4. I end up with background sky levels of around 20-25ADU, and going by the 20x rule, 20 ADU is 40e- which is 20x greater than the 2e- read noise. Achieving skyfog limited narrow band subs in 600 seconds is unheard of... Also keep in mind, the longer the exposure, the more severe the amp glow will be. The glows grow relative to the temperature of the circuits causing them, which is out of sync with the baseline dark current. Very long exposures with this camera tend to be detrimental to IQ due to the glows, as once they overtake the dark current, they can introduce significantly more noise. If you are imaging at a slower f-ratio, you should be able to get NB exposures that are even longer than 900 seconds, although to be quite frank, i personally do NOT see that as a good thing. ;P I prefer shorter subs myself...safer, easier to keep things in focus, less loss to frame intrusions, wind, other environmental losses, or cable tug or mount issues, etc. What matters is whether you have sufficiently swamped the read noise. Doing that with this camera is FAR easier than pretty much any DSLR or CCD camera on the market, with the possible exception of just a couple. |
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Thanks for the great discussions regarding the Gain/Offset for this camera. I've just taken my first shots with my 1600MM cooled and Celestron EDGE HD 8 with 0.7x reducer at Gain 0/Offset 15 and found I had bloated stars with 300 sec exposures (with DGM NBP filter). I will try Gain 75 /Offset 15 and see if I can reduce the exposure times and hopefully the star bloat. It's quite different from a traditional DSLR! The reason for bloated stars could be oversampling. At 1400mm FL you get 0.56"/pixel resolution. I would try binning, reduced exposure times would also work though. |
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Thanks for the great discussions regarding the Gain/Offset for this camera. I've just taken my first shots with my 1600MM cooled and Celestron EDGE HD 8 with 0.7x reducer at Gain 0/Offset 15 and found I had bloated stars with 300 sec exposures (with DGM NBP filter). I will try Gain 75 /Offset 15 and see if I can reduce the exposure times and hopefully the star bloat. It's quite different from a traditional DSLR! Aye, different from both DSLRs and CCD. This camera actually probably has more in common with a DSLR than a CCD, however it still is mono, so operationally you use it more like a CCD (i.e. with filters, etc.) The main difference with CCD is the variable gain, which can be thought of as a very finely delineated ISO setting on a DSLR. You have 300 "ISO" settings, instead of just 10, or maybe 30 with third stop settings. You also have a variable offset, which is usually fixed in a DSLR. Just as higher ISO on a DSLR is usually better, so, too, are higher gain settings on a mono CMOS camera. Just beware...increasing gain on this camera also comes with a loss in dynamic range, same as with a DSLR, so choose wisely (slower scopes can usually benefit from higher gain, while faster scopes will benefit more from a lower gain, however avoid going below Gain 75). |
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Jon Rista: Jon, you were asked by several people (including me  ) , why Gain 75 and not 50 or even 0 for long exposure? Could you please explain?
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David Dvali:Jon Rista:Jon, you were asked by several people (including me Read my last couple of replies. I quoted and responded to your question directly. ;) |
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Jon Rista: Thank you Jon, I overlooked it somehow |
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I know we've discussed this at length over at Cloudy Nights but feel I should comment on why I choose to image for the last few months at zero gain. I agree with everything that has been said about quantization and read noise, but I think there may be other considerations based on the user. I, for example, have been broadband imaging (LRGB) from a moderately light polluted area. For broadband, the skyfog noise is by far the largest noise term. In this use case, I feel the contributions from quantization and read noise can be considered negligible. I'm not arguing that low gain will ever be as good as a higher gain, but rather that the apparent difference isn't significant once you stack 100+ subs. I say this because it brings up another point about the camera. At zero gain, in my area, I'm limited to 180s subs. In rough numbers, at 75 gain, this turns into 72sec subs (2.5x) and at unity this turns into 36sec subs (5x). Unity gain turns into 100subs per hour! Now any user of this camera can appreciate the data storage requirements can become a problem. It's easy to dismiss zero gain as sub optimal, but there are other considerations that may be worth thinking about. Now, get back to setting up that NAS and compressing files for archiving. |
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| Since we have the same setup (telescope + camera), I'll try a few of your settings Jason. So far I've found that is not only the # subs/hour, its the accumulated download time too. What USB 3 speed do you typically use? |
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| Excellent point about high LP, Jason. If you have enough of it, it should be easy enough to drown out the read noise. And at 180s, the glows won't be a problem either, so it sounds like a viable solution. I think I'll give Gain 0 with LRGB a try myself. Pleiades is coming around. I grabbed some Gain 75 data on it a couple nights ago...I was at 20 second subs with my L filter at f/4... O_o |
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Yeah, the camera makes data at an amazing rate. Regarding the USB3, I use the lowest setting of 45? (I think that's it without looking). Downloads should happen in less than 1 second. If not something may be wrong. Some capture programs analyze the frame before displaying it (like SGP). This can take a couple seconds more. Are you using a hub or have more than one device on that USB port? But it's still a good point about the benefit of longer sub exposures. It reduces that interframe overhead which can seriously eat into integration time. |
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Yes - you're right Jason - With SGP, it does a star analysis even though one is doing flats, darks, etc. and that adds a several seconds to each frame. Regarding USB3, I just have it plugged into my USB3 port on a laptop. It seems to work just fine. Thanks again to you and everyone else for assisting us Newbies! The discussions are very informative. |
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[img width=545,height=396]http://cdn.astrobin.com/images/thumbs/7ccbfa152f743ea4c8aad1fa0b8d187e.1824x0_q100_watermark_watermark_opacity-10_watermark_size-L_watermark_text-Copyright%20Carlos%20Uriarte.jpg[/img] I love my serius first image with ASI 1600MMC. Settings: 200gain/60offset 12 subframes 600s at -30ºC Without darks and 60 bias. I think that it's a gamechanger camera 8) Love USB3.0 speed with maxim DL and 2 USB2.0 HUBS from camera. My telescope is an William Optics zenithsar 10th aniversary edition Fluorite Doublet. With W.O. flattener IV. 440 focal lenth.at f/5.6 I waiting for arrive my new telescope: Takahashi FSQ106 with 3,9 focal reducer. <3 |
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 Here is my first image with my 1600MM Cool. The camera is everything I hoped it would be. This is 40 x 120sec at f3.9. Gain 200 & Offset 60. Thanks to everyone for sharing their thoughts on settings that allowed me to go straight in and get this. Borg 125SD & Super Reducer. Chroma 3nm Ha. |
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Here is ins mine, first light, zwo asi 1600mm-c, skywatcher apo 120ed, 1x 600s Ha, OIII, SII gain 110, offset 0 (i didn't knew ...), 20 darks, 20 bias  |
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Dear all, I don't know but may be I am wrong here with this topic. Regarding creating BIAS/Offset frames: I used Unity gain settings with the shortest exposure time (1/320) My question: Should I use gain 0 for BIAS/Offset frames? Because the frames aren't completely dark! I am using APT 3.33 as Imaging software. Regards Thomas |
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| You should use the same gain and offset that you use for imaging. The shortest exposure possible with the ASI1600 is 0.000032 seconds. |
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Don't think I've seen this published anywhere, but based on the presets loaded in the ASCOM driver and the suggested 75/15 gain/offset, it appears there is a relatively simple formula for determining the offset for a particular gain. offset = 10^(0.00233*gain+1) Does anyone know if there is a way to save new presets, such as 75/15, in the ASCOM driver? Ron |
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Hi all, i've received new Asi 1600 mm-c pro but I have to learn a lot of things. I'm reading this very interesting post and I have a question: if I change gain, I have to do change dark frame too (I'va done library of 50x30", 50x180", 50x300", 250 bias at -20°, gain 139). Sorry for my english :-) Vittorio - Venice, Italy |
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Hi Vittorio, yes when you change gain I would definitely use different darks for that. It is actually quite easy to see, when you shoot 60s darks with gain 0 and 60s with gain 139 and stretch the darks you will see a lot higher amount of faint amp glow. Actually the ASI is my first cam where I needed to use "correct" darks. Normally I only used Bad Pixel Maps but with the amp glow the calibrated subs only look great when I also substract the darks. Also have a look at this topic here: https://www.cloudynights.com/topic/573886-sub-exposure-tables-for-asi-1600-and-maybe-qhy163/ The ASI is so sensitive, you burn stars quite easily. I (more or less) follow the above guide and only expose with 30s with gain 139, for L and RGB with my bortle 4/5 sky. In theory I would even have to go a bit lower for my L but I will try first to see if there is a difference. Thanks to Andrea Alessandrelli who actually helped me finding out all this Best Frank |
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Thanks Frank, I have to learn how evaluate noise level (I use pixinsight, but I'm not sure about the setting to use :-( About flat frames...there is a correct ADU range? Thanks Vittorio |
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I had good results with flats shot at 0.01s but I didn't approach this very scientific. Other people propose an ADU count of around 9-12k. https://www.cloudynights.com/topic/545128-flats-exposure-for-asi1600mm-cool/ Will also have to try this tonight |
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Thanks, I think it depends by used filters too. :-) Now I'm trying just narrowband, too much things to do  |
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This is a great thread. I am new to imaging, at least with this camera. But can anyone tell me that with each gain/offset setting do you need to have a different series of bias & darks? I assume that you would have a new series of flats. Thanks, Brent |
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Hi, I did get my 1600 in February and have taken som images with my Boren Simon 8" f/3.6, mostly at unity gain. Now I have got a WO Spacecat 51 which I will try with the camera. I have read that it is not an ideal combination but will try to see what I can obtain. I would like proposals to gain and offset for the combination, I planned to use 200/50 with NB filters. 6nm HA and 3nm OIII and SII. Plan to take 180-300 sec. exposures with dithering. Could that be OK? Proposals to LRGB would also be very welcome. Erik |
