symmetal

Oops. Your right Wim. Forgot the k The FLT98 and ASI6200 images at 1.2"/pixel so gives fairly detailed images near the limit of seeing, and due to the full frame sensor has a wide FOV of 2.3 degrees. I can crop just the object in question which I've done below for you, 🙂 though I find the wide field views show many extra little galaxies and features, so I've posted the full images. I've found that not all images show full size when clicked on, so I usually right click the image and select show in new window, which does allow the full size image to be viewed. Dwarf galaxies are very faint objects so are not easy to see, which is one of the reasons I've imaged them, being a bit different to the usual deep sky images imaged, and get overlooked. 😊 They need fairly long image durations, and plenty of them, to reveal the faint galaxy stars and a single sub will show nothing of it. The LX200 is on a fork mount and so isn't really suitable for long exposures. I just use it for planetary. Here's a full size crop of the Draco Dwarf from the full size image. It's the rough cluster of faint stars in the centre 'behind' the Milky Way stars in the foreground. Like all the local dwarf galaxies they are not very spectacular and have no 'wow' factor, but are interesting in their own right. If I stretch the image too much the stars lose their colours and even longer integration will show more of the stars. Draco Dwarf Galaxy (full size crop) Alan

Continuing my Dwarf Galaxy collection here's the Draco Dwarf Spheroidal Galaxy. Five hours total LRGB using FLT98 and ASI6200. Processed in Startools and PS. It's a satellite galaxy of the Milky Way, 260 ly distance, discovered in 1954. Some interesting facts are that the vast majority of its stars are variables, and it's the most dark matter dominated object known, (in 2007), so is a key object for the study of dark matter. It's also dust free, containing insignificant amounts of interstellar matter. Click to view them full size. 🙂 Given a heavy stretch there is some IFN visible. Alan

I did a test of the variation in Bias Standard Deviation from gain 0 to 100 on the ASI 6200 to compare with your bias Gain/SD chart you posted a while ago Tom. Here's the result which seems as expected. Gain 60 is actually 6dB and the range of min to max ADU changes from 204 at gain 0, to 418 at gain 60. This is roughly double, which corresponds to a doubling (6dB) of amplifier gain in the camera. Likewise the SD roughly doubles from 4.56 to 8.73. These are from single frames but if you took the average of many frames they would be closer to actually being double. Gain 100 is where the HCG mode kicks in and the ASI Ascom driver won't allow you to select a gain higher than 100, which is equivalent to 10dB. The ASI gain is in 0.1dB steps. I then plotted your Atik figures you posted and overlaid the ASI figures on top. I changed the ASI gain steps to dB to keep the same x axis. This suggests than your Atik gain steps as entered manually are not actually in dB steps as the increase in SD is far to small, and seems to be closer to 0.1dB steps like the ASI. If you plot the Atik 35dB SD value as 3.5dB the Atik and ASI graphs are of a similar slope. Tom, I think you need to query the actual manual gain step size with Atik, as well as the huge and unusable gain settings apparantly applied by the Atik Medium and High gain presets. Along with not allowing the built-in HCG mode to be enabled. Alan Edit: I've replotted the above graph assuming the Atik gain steps are 0.1dB and here's the result. The Atik is showing slightly higher noise overall for some reason, but the two graphs now agree closely on the change in SD with gain.

Hi Tom, Yes, those fits gain settings don't make any sense. The Sony datasheet for the IMX455 states max 36dB of gain. Can you confirm that the gain setting on Low is reported as 0 in the fits header. Also if you post the Low, Med and High EGAIN settings from the fits headers it will give an indication of the actual gain being used. I assume Atik haven't replied to your email yet. Alan

Can't complain about your new Redcat George. Good stars in all four corners too. Better than mine which has slight coma in one corner. Bet you're relieved. 😊 I like the 3 way dovetail splitter. 😀 Alan

I forgot to say that the fits header will show the GAIN and OFFSET values of the image, hopefully with actual values for the gain, and the EGAIN entry will show the electrons/ADU value from which the gain can also be determined. If you post those values for the LOW, MEDIUM and HIGH presets it will be useful Tom. 'Astroart' or 'Fits Liberator' will display the fits header. 😀 Alan

It would be interesting Tom to see if SGP reports the actual gain setting used in the filename, when you do a test image with Medium and High Gain presets. As it stands Medium and High seem to have a far higher gain than you'd ever want to use. Alan

HCG is a feature in the latest Sony sensors. It's built in to the sensor circuitry itself as one of its readout modes. There is a LCG (Low Conversion Gain) mode too for use in bright conditions but astro cameras don't enable that mode. 😀 All the ADC conversion circuitry is built into the CMOS sensor chip too. Each sensor column has it's own ADC circuitry, so there are 9576 ADC converters on your IMX455 sensor, unlike CCD sensors where there is one ADC which is on a separate board to the sensor. So the HCG mode is there if Atik choose to enable it. As you use SGP Tom, like me, you probably aren't yet aware that the gain and offset can be set in SGP too which can catch you out. I just set it in the Ascom driver and don't let SGP change it but I do enable the gain and offset to be inserted into the image filename as a convenient check. If you insert _%cg_%co_ as part of the SGP filename template you'll get a filename similar to this M31_Lum_60sec_gain_100_offset_50_1x1_-15C_2021-09-06_frame44.fit In the SGP control panel you can set gain and offset for the whole sequence here, though I leave it 'Not Set' so it uses the Ascom driver value. You can set higher gain when binned for quicker autofocusing if you wish. In the Sequencer itself you can click on the cogwheel next to each event here which will bring up another panel like this where a different gain and offset can be set just for that event. SGP checks the event setting first and if it's not set there it checks the control panel setting, and if it's not set there it uses the Ascom driver setting. Hope this helps. 🙂 Alan

As the camera gain increases the noise range from min to max will increase as well, likewise the SD. You therefore need to increase the offset to ensure the min value stays above 0. Your Medium and High presets both seem to have a very high gain setting so even with the higher offset applied it's not enough to avoid the black clipping. The power settings could be USB speed settings as you say. The Atik manual doesn't mention whether ROIs can be set for planetary imaging. Without a ROI the frame rate will be very low on such a large sensor. Alan

The SD values on MED and HIGH are fairly similar but both way higher than on LOW. As these don't match the SD values at higher gain when set manually, which as I mentioned before seem too low at the higher gain settings, it's a bit of a mystery. It looks like the preset LOW setting is the only preset to use for DSO imaging. It would be useful to test the manual gain settings using a flats panel or similar, to see if the manual gain settings do work as you would think. At gain 6 you should get a signal gain of x2 compared to gain setting 0, so your flats ADU peak value should double. Likewise gain 12 should give a x4 signal gain over gain 0. Gain 30 is a x32 signal gain. Alan

Yes there seems little real difference in the noise in the three power modes. I'm not sure what the LOW, MEDIUM and HIGH settings refers to as Medium and High show a large min to max change with black clipping present. Power Save Medium and High show black and white clipping too. I'll be interesting to hear what Atik say concerning the HCG setting. Alan Edit: It looks like Low, Med, High are possibly preset gain/offset settings with Low being gain 0 as the SD figures agree with your SD table. Med and High show much higher SD values than your SD table on the right. I'd have thought the SD would be significantly higher at higher gain settings than your right SD table shows, so not sure if the higher gain values are being set correctly when entered manually. The preset offset value of 200 is a bit low at LOW setting though is just avoiding black clipping. At MEDIUM and HIGH the preset offset is too low but in Power Save mode it white clips anyway so no offset value entered here would be much good. 🤔 Does it display what the actual gain settings are when you preset MEDIUM and HIGH.

You can do it at room temperature just for the test. Just try gain 0, 10, 20 at offset 500 with the different power modes. Alan

Possibly. It's worth doing the tests in normal mode and see what the SD figures are for comparison. Alan

Hi Tom, From your results there is no indication than HCG mode has been enabled at any gain setting. The noise SD just increases with gain just like with a camera without HCG. HCG is built into the sensor though I expect there is an option to enable/disable it via software. I think it's worth dropping an email to Atik to query this as this is a major selling point of cameras with HCG sensors. However, your SD figures are similar to what I have at gain 100 (your gain 10) when HCG is enabled on the ASI, which may imply that HCG is enabled all the time on the Atik. 🤔 At room temp I have SD 5.9 with HCG on and SD 12.9 with HCG off. Regarding offset I would think that 500 is a reasonable figure which would give you ADU minimums of around 350, though offset 400 would be OK too if you wish. Alan

That's disappointing Tom. Without the camera cooler running the power consumption is less than 1A and the ASI can be powered just from the USB3 connection, though a laptop may not supply enough current via USB3. I assume you were using the cigarette connector too. It does look like a power issue though as USB speed issues only arise while downloading and you have difficulty connecting. My mini-PC on the scope will often hang downloading if the USB3 speed setting on the ascom driver is at 100%. I have it set to 75% and have no issues. You don't seem to have that option though so that must be set automatically on connecting. The Atik has a standard 2.1mm centre positive connector so any generic 12V power supply you have supplying 2A or more would work for testing if you don't have the cooler running. Alan

TIFF or TIF files, (they are the same thing), can be in many different variations with multiple layers and compression types and many programs just accept basic uncompressed tiffs. If I have this problem I just load the tiff into Photoshop and resave it as an uncompressed tiff file. This usually solves the problem. Any good free image processing program like Gimp or Irfanview etc. should be able to do this as they should be able to load any tiff file format. Alan

A quick check to see that the HCG mode is enabled in your Atik Tom is to take 2 bias frames, one without HCG and one with and look at the results in Fits Liberator or similar fits viewing program. On the ASI6200 HCG is enabled at gain 100 and above. Here are my results below for gain 100 and gain 99, (HCG disabled) Note the difference between min and max ADU values and the Standard Deviation. HCG on, SD is 6.0, HCG off, SD is 12.9. This is at room temperature too. As your gain settings appear to be in steps of 1dB, I suspect it will be enabled at gain 10 on the Atik, assuming it is automatically enabled on the Sony sensor chip rather than being set by the controlling software. You can take test bias frames at say gain 0, 5, 10, 15, 20 etc and see where the read noise decreases sharply, ie the SD drops noticeably. That's where the HCG mode kicks in. That's the gain setting I would use all the time. 🙂 Also, you can see if your offset is good too while looking at the bias frames. The minimum ADU value must be significantly above 0 to avoid black clipping. It's 368 ADU on mine at gain 100. My offset setting is 50, with an offset increase of 1 increasing the output ADU by 10. Offset 50 therefore adds 500 ADU to the output which you'll note is where the peak of the bias histogram is, also corresponding to the image mean or median value. If the offset was 0 then the peak of the bias histogram would be around zero too and the left half of the histogram would be clipped to black, which is bad. I could get away with offset 30 without clipping, but I left it at the default 50. The tiny loss of dynamic range due to the offset being too high is insignificant. As your offset is in ADU steps of 1 rather than 10, I would start with offset 500 and see what the bias looks like. Aiming for a minimum image ADU of at least 200 to 250 should be fine. Note that as the gain is increased the offset may need increasing too to avoid black clipping, but you'll most likely only use the camera at the one gain setting where HCG is enabled. 🙂 Alan

Yes, I'm surprised that the Atik manual gives no graphs at all. If it has an HCG mode I'd have thought the manual would have mentioned it. 🤔 The Zwo ASI6200 graphs are almost identical to the ASI2600 graphs apart from the read noise being almost constant above Zwo gain 100, implying there's no real point in exceeding gain 100. In fact the Zwo driver only allows gain settings from 0 to 100 The Zwo ascom driver has the USB speed setting if needed to get reliable downloads. I notice the Atik has gain settings from 0 to 36 and offset 0-4095. This implies the Atik gain is in dB steps while the Zwo gain is in 0.1dB steps. Also the Atik offset is likely in steps of 1 ADU (at 16 bit) while the Zwo offset goes from 0 to 200 and is in steps of 10 ADU (16 bit). There's no mention of an anti-dew heated front window in the Atik manual either. 🤔 Another difference is in the Dark Current. Atik quotes 0.03 e-/pix/sec at -10C This is the Zwo dark current graph Here 0.03 dark current is at 20C and at -10C has a dark current of around 0.00098 e-/s/pix. e-/secs/pixel and e-/pixels/sec are the same thing I would have thought. Here's the above graph plotted linearly. and the bottom section expanded Alan

Thanks again for the detailed reply @vlaiv I think I've got it. 😊 I was initially confused by the first line of your reply, which seems to contradict the equation from the linked web page, dark noise = SQRT( dark current * exposure length). Further down you said which again seems to contradict your first line. However, what you mean is that the noise component of the dark current signal increases more slowly than the target signal for increased sub length. The dark noise level you end up with is dependent only on the dark current signal which is dependent only on temperature. I was doing my initial calculations only on dark subs so there was no target signal to consider. For a single sub the read noise is fixed and I was comparing the increasing dark noise with sub length as something to be concerned about. But in reality the increasing target signal with sub length always outpaces the dark noise increase anyway. I found answers on the web saying thermal noise is white noise independent of frequency, and dark noise is shot noise which caused confusion. However from this lecture which agrees with what you said, they are the same thing. I'll discard all the excel files I've made as they don't mean much when actual target signal is taken into consideration. 😁 Thanks again vlaiv for taking the trouble in pointing out the error of my ways. ☺️ Alan

Thanks @vlaiv for the quick and detailed reply. 😀 I agree that the dark current is dependent only on temperature, but the dark noise which is what affects our images is dependent on sub length. A short sub will have less dark noise than a long sub. At a low enough temperature the increase in dark noise for long subs is negligible which is why we can use bias as darks on some cameras. From here dark noise = SQRT( dark current * exposure length) I thought that thermal noise and dark noise were essentially the same thing, though dark noise does have a shot noise element to it so is dark noise = thermal noise + dark current electron shot noise, or are they separate entities? Getting a bit confused here. 🤔 Is camera Amp glow effectively due to varying dark noise and/or thermal noise over the sensor due to localised temperature variations which increases with sub length, so darks are a necessity? My initial reason for the post is that as the dark noise increases with sub length there comes a sub duration when the dark noise becomes significant. At low enough temperatures this doesn't matter. On this lecture by the author of Sharpcap at 22:18 he compares thermal noise contribution compared to light pollution and why it's unnecessary to cool beyond a certain temperature if you have light polluted skies as the thermal noise is insignificant. I just chose read noise as a figure to use for comparison to where the accumulated dark and/or thermal noise remains at an 'acceptable' level where the dark/thermal noise is not significant. Hope this makes sense. Alan

I don't think @vlaiv got my notification last time as it wasn't highlighted. 🤔 At least I'm hoping that's the case and that he didn't ignore me. 😬 Here's a graph of the above table. However, I now think the results as shown are valid only for unity gain and that dark current would increase linearly with camera gain. The ASI6200 has no unity gain setting, with ASI gain 0 having a gain 0f 0.79 e-/ADU, and the usual ASI gain setting of 100 having a gain of 0.26 e-/ADU. Should the dark current figures used in the equations above be multiplied by 3.85 (ie. 1/0.26) which implies at higher gain settings the dark current is more significant than originally thought? Alan

For something to do I thought of calculating the maximum exposure durations where the accumulated dark noise is not too high compared to the read noise for various sensor temperatures and so doesn't significantly affect the image. It's often stated that sensors needn't be cooled to -10C or below as the dark noise will still be insignificant at higher temperatures. I cool my ASI6200 to -15C but thought this may not be necessary. I thought of discarding my darks and using the bias as darks instead as there is no amp glow on the later Zwo cameras, so the dark noise needs to be determined. Here's the Zwo dark current graph for the ASI6200 These are difficult to interpolate as the dark current scale is exponential. I plotted the values on the right (taken from the graph) in Excel with linear axes here The low temperature values are still hard to interpret so here is that part of the graph expanded. I made some Excel calculations to work out the exposure duration where the accumulated dark noise is half the read noise of 1.5e- and so doesn't make too much of an impact. Here's the results and the calculations used. This implies that for L exposures up to 2 mins 0C is fine, for RGB up to 6 mins -5C is fine, though for long narrowband exposures -15C is preferred. It would be good for @vlaiv to verify my reasoning and that the calculations are correct, 😊 if he has the time. I've used read noise as a comparison as that's the figure used in sky background noise exposure calculations. If the dark noise adds little to the read noise it doesn't affect these calculations. Alan

"ALL YOUR IMAGE ARE BELONG TO US." Alan

Optimised for DSLR just means it has a 55mm backfocus distance. Any sensor, DSLR or not, placed 55mm from the FF would be fine. Using the 16.5 and 21mm spaces along with the camera's 17.5mm backfocus should give the 55mm required. Are you using a filter between the FF and the camera? The ASI071 response graph extends significantly into the IR with a similar response for RG and B beyond 800nm. It doesn't show the response of the protect glass, so there is no UV-IR cut filter in the way, which could lead to out of focus IR giving star bloating in all three colours. So a UV-IR cut filter is needed somewhere, possibly screwed into the rear of the FF. Note that if the filter is between the FF and the camera you need to increase the above 55mm spacing by 1/3 the thickness of all the glass in the way. The camera protect glass should be included here as well, so 56 to 56.5mm spacing is a better figure to use. Alan

I use a desk fan blowing though the camera vent slots if I'm taking darks indoors and struggle to reach the temperature. This gives me about 10 degrees more cooling capacity. Alan