symmetal

After all my troubles with the RASA 8 and dropping my RASA 11, I'm finally back in business. 😊 Had a few days of clear nights with no Moon a few weeeks ago so managed a few targets which I'm just now starting to process. I also bought PixInsight a few months ago as I wanted to take advantage of BlurXterminator and with the help of Warren Keller's book and YouTube tutorials I've got it figured out to a useable degree. 😁 I also only discovered the Generalised Hyperbolic Stretch add-on a few days ago which makes stretching much more controlled, though you need to view the tutorial videos a few times to understand how it works. The 'Symmetry Point' control is very powerful in deciding where you want to apply the most stretching. Also first time of using star removal which was great at reducing the rather flarey bright stars effects RASAs produce. Had trouble with it removing all the stars until I realised that StarXterminator works on a linear and not a stretched image like others do. This is useful as BlurXterminator and NoiseXterminator can be used fully on the starless image, and a modest BlurXterminator on the star image alone. I found NoiseXterminator produces significant star artifacts on a normal linear image with stars, which can be seen if you look at the before and after linear image, where a host of clipped coloured pixels appear where unclipped stars existed before. Running NoiseXterminator on the stars only extraction produces horrendous results as I suppose there is no real noise to analyse and it goes haywire. Here's my first image of the Dark Shark Nebula which is composed of 2hr 44 mins of 2 min exposures with the RASA 11 and ASI2600MC in Bortle 3 skies. PS was used to blend the stars back in and clone/patch out any obvious residual star artifacts on the starless image. I haven't posted the annotated image as it just found one entry of PGC67671 on the right. Alan

That's a very interesting image. 🙂 If you reduce the stretching I imagine Polaris B becomes distinguishable, but can you also resolve Polaris Ab? Alan

You confused me as the title says Sh2-76 while the image is Sh2-73. Sh2-73 is in fact a reflection nebula and classed as IFN. It was included in the Sharpless catalogue by mistake. You managed to get something though which is quite a feat. 😊 Alan

By the size and the sheer number of 'craters' i would also go with dew on the sensor window. The 26C does have a variable setting for window heating I believe, so make sure it's turned on. If they're on the sensor itself the spots would be in focus and if on a filter, which you're not using anyway, they would be significantly larger. They possibly changed size or position between imaging and taking flats leading to the cratering effect. As long as the camera gain is the same you can use any software to take the flats, the gain is specific to the camera and not the software. Alan

Excellent. That's one of the best Moon images I've seen. 😊 What's the bandwidth of the 520nm filter and the exposure used. I've used a Baader 10nm solar continuum filter at 540nm for the Moon with good results, FLT98 and 2x Powermate, but it doesn't quite match yours. Your extra 40mm aperture would make a significant difference I imagine. 🙂 Alan

Yes, I prefer your latest version too. The previous one, to me, looked like a picture of IFN in which lurked a couple of galaxies struggling to make themselves seen. 😊 Personally I would still bring the IFN down more so that it's just a noticeable variation in the background, seen when you examine the image more closely, with the galaxies being the main subject and significantly brighter. 🙂 Alan

Here's two more from the same time, with different filters, showing different structures. These are actually from Goes 18 but I forgot to edit the captions. Alan

The GOES-R weather satellites also have a SUVI (Solar UltraViolet Imager) sensor. They transmit solar images every 4 minutes using 6 Extreme UV filters and NASA posts them to download around a day or so later after processing. The L2 (level 2) are the best to use as they are HDR composites of short and long exposures. The sensor is 1280 x 1280 pixels. and the images appear to be rotated, leading to blank triangles on the image corners though these may be calibration features. The SUVI images are fits files, encoded as 32 bit floating point, so many programs that work with 16 bit integer fits files won't load them. Fits Liberator will though and you can save them as 16 bit tif files, as long as you move the histogram sliders to their end limits to avoid clipping data beforehand. Here's the extent of the prom that erupted on 20 Apr after stretching and colouring using PS. I used the colour NASA associates with each specific filter, red is used for 304 angstroms. This wavelength shows proms and CME the best. I'll post some of the other filters later. 🙂 Alan

The main contribution of the luminance is in improving the S/N of your image as it will gather signal around three times quicker than the RG or B. Hence them being overexposed if you used the same exposure time. If the background noise in your processed image is more noisy than you would like then adding some luminance will certainly help. Depending on how well colour corrected your scope is, the luminance may actually be softer than the colour channel images as it can't separately focus for the specific colour bands when using luminance and must use an 'average' focus position which best manages the full spectrum. Alan

It's the EQASCOM driver you need to install from EQMOD. This is the EQ5/EQ6 and their variants driver which also works with EQ3 and EQ8 models. There is no other driver needed for the mount. You have the EQDirect (EQMOD) cable too so you're all set. When you've installed EQASCOM and you select your mount in your capture software, select 'EQMod AscomEQ5/6' as the mount. On the driver configuration screen before you can connect to your mount you need to enter the COM port used by the EQDirect cable and set the baud rate to 9600. Chris Shillito (author of EQMod) has a useful video on setting it up and getting it working. 🙂 The GS Server is a more recent substitute for EQAscom so if you have installed that you don't need EQASCOM but will still need the cable. GSServer is free to download though you have the option to donate something to the developers as a thank you. Alan

That's most impressive George. Is that with the 2 min L and 3 min RGB subs? Be interesting to see what the ASI6200MC and L-Pro does as a comparison, to see if the LRGB looks better. Alan

As you have a OSC, yes, that would be the best bet for you to use along with the L-Pro. Much less subs and flats to deal with. In the past mono LRGB gave better results than OSC, but the more recent cameras have narrowed that gap considerably. Your ASI2600MC is a newer camera compared to the ASI1600MM so is even more efficient, leading to shorter exposures as optimum, which isn't really what you need, so if 2 min exposures are still badly overexposed you can use the 2600 at 0 gain rather than the usual gain 100, and 3 min exposures or so should then give good results. You lose the lower read noise feature of HCG below gain 100 but with your light pollution that won't matter, as your exposures will still swamp the higher read noise at zero gain. Even at gain zero the ASI2600 is above unity gain, so the discarding photon issue of the ASI1600 doesn't apply. 🙂 Here's the exposure chart for the ASI2600 (MC or MM) which gives you the optimun ADU values so you can judge your results. Assuming you're using the default offset of 50. Alan

Yes, the wind was annoying last night. I had to give up in the end and discarded all the subs. 😟 Your latest postings are a little difficult to interpret as the sky brightness seems to vary quite a bit between exposures as they're pointing in different directions due to the time difference, and the light pollution is probably changing. I've posted the results after loading into SGP and on the preview I put the black point at 0 and brought the white point down to around 30000 ADU so a direct comparison can be made. The Green image was the best as far as exposure goes. It was taken at 01:00 so the sky was likely at its darkest. The sky background is still at around 7000 ADU though. The Blue image has a much higher sky background at around 13700, much the same as your 600s Red from the previous postings. It's taken at 04:00 so not at the darkest hour, and it's possible the scattering from the light pollution has produced a higher blue sky background like sunlight scatter gives a blue sky. The Luminance taken at 22:51 has a similar sky backround to the Blue at 14300 ADU and is just after astro dark has begun so not as dark a sky as the Green. It's not peak white like your previous Luminance post was though. 😊 You posted two green rather than a red so can't assess the red this time. In conclusion I'd recommend you use even shorter exposures, around 1 min for L, and 2 mins for RG and B. They'll still be overexposed compared to optimum exposures as calculated where 2000 ADU background is preferred, but if you can cope with having all the extra subs to work with it should be beneficial. If you use dither you can set to dither, say every 8 frames for L and every 4 frames for RG and B to avoid wasting too much time having the mount settle after a dither. With your skies, the narrowband imaging you normally do is the best choice, but at this time of year there aren't many NB targets so you're stuck with wideband for galaxies. With your skies, a OSC camera would have likely been better for you for wideband, as you would have less subs to deal with, but as you have the mono camera and filters you may as well make use of them. Some may suggest using 0 gain on the camera to enable longer exposures, but I'm not a fan of exposing below unity gain as all you're doing is throwing away photons. At unity gain 1 photon gives 1 ADU in the camera (at 12 bit). At gain zero, 5 photons gives 1 ADU in the camera so you're just discarding 4 photons out of 5 in reality, and you'd need to expose for five times long to get the same signal as you get at unity gain. The increase in well depth at 0 gain is not so significant in practice. Hope this helps. 🙂 Alan

Here's the histogram of your 10 min Red image. The top one is the full black to white range. The signal starts well away from the left (black) edge of the histogram so you're throwing away about 20% of the dynamic range capability of the camera. You want the histogram peak corresponding to the sky background close to the left edge with just a bit of white space below it just to ensure the black signal isn't being clipped. The ADU measurement method in the previous post are just a more accurate way of getting the optimum exposures. See what your 3 min RGB exposures histograms look like. The gap before the histogram starts will likely be about a third the size of the image above which will be better but still larger than optimum. It's a trade off between optimum exposures and how many extra subs you're willing to deal with. Your luminance will be the most critical on exposure, so see what the ADU values and histograms look like for your 1, 2 and 3 min tests. I suspect that even the 1 min exposures will still be longer than optimum but will likely be the best compromise. Alan

For your narrowband or dual band filters your 300 or 600 sec exposures are fine, as those filters let through much less light than broadband filters and long exposures are needed. There's no chance of overexposing with narrowband filters. The L-Pro would likely be better with around 2 mins or so in your skies. 🙂 In your capture program just hover the mouse over a patch of background sky in the image preview and see what the ADU reading is. The median ADU value from your image statistics will likely have a similar value if there isn't a lot of nebulocity around. If this ADU figure is between 2000 and 3000 then your exposure is fine. Exposing for significantly longer than this will just blow out your highlights more and reduce the image dynamic range. Alan

Yes, your exposures are much too long for CMOS cameras using broadband filters, particularly luminance. You only need to expose for long enough where the noise from the sky background is significantly higher than the read noise of the camera, ( a factor of 5 higher is considered a good figure to use). I've made spreadsheets for various cameras detailing this and this is the one for the ASI1600. At unity gain 139 (as you've used) and the standard offset of 50, a sky background of 1965 ADU is all that's needed to swamp the read noise by a factor of 5. Inputting your 600s exposure and 14000 sky background ADU into the calculation below the chart, your optimum exposure for Red is only around 54 seconds. You must have significant light pollution where you are, which keeps your optimum exposure durations fairly short. As luminance lets through around 3 times the light of red, (probably higher as the camera will be more sensitive to green, your optimum luminance exposure would be only around 15s. This would mean taking loads of exposures to get your wanted integration time so to save having hundreds of subs, compromise by trying 2 min each of RGB and 1 min for luminance. That should get you better looking subs. Alan

Plenty of detail there Olly. Thanks. Is it just RGB or is there some NB added? I see you caught the spider but not the fly. 😁 Alan

I have a set of 2" Astronomik 6nm MaxFR Ha, OIII & SII filters (f1.8 to f2.2) to use with the RASA 11 (f2.2, 620mm) and ASI6200MM so can give it a try, when it comes around, if it's confirmed to be a genuine feature. 🙂 Alan

If the ASIAir allows you to do a two or three star alignment then it means it has the capability of keeping its own internal sync point map of the night sky to correct for polar alignment errors. There may be an option to sync the mount with every successful plate solve which you can perhaps turn off, or to have an option not to maintain an internal map of successive sync points and just use the last one, which is the better option if you're always using plate solving. Another ASIAir user may be able to say what options are available. Alan

I use SGP and it includes a useful 21x21 sample under the cursor. The whole image mean and median is quite close to the more accurate sky background sample under the cursor as the vignetting tends to counteract the highlights, if there's plenty of sky background in the image. 🙂 This is a OSC image. If the mean and median are close the whole image values are pretty good to use. Alan

Thanks vlaiv. In my previous mentions of this subject I did say that in heavy light pollution the exposures in NB may be achievable, but didn't mention it here. In Bortle 3, I found I would still need around 2 hours NB exposure even with the RASA 11. It looks like you've sorted it out with vlaiv's help, but to recap. You shoot to a required ADU as given in the table, as at that ADU the sky background noise sufficiently exceeds the read noise, making the read noise contribution to your image insignificant. You can then start another exposure, rather than continuing with the first exposure, and so avoid blowing out the highlights more than necessary, or risk tracking errors or aircraft etc. spoiling your image. All my calculator does is avoid you having to do multiple test images to achieve that ADU value. Say you need to achieve 3000 sky background ADU as read from the table using your gain setting. Checking a previous image of say 2 mins exposure, (at that same gain setting), you read off the sky background as being 2600 ADU. Putting these values in as the sample image, and 3000 as the required ADU the calculated exposure is the exposure needed to achieve 3000 ADU with your setup. It just subtracts the bias value from the ADU values entered and proportionally adjusts the ADU/exposure values. Nothing fancy. If you put the sample exposure in seconds the result will be in seconds. If the sample is in minutes the result is in minutes. Alan

Yes, it's the noise from that sky background that does the read noise swamping. Different filters would just need different exposure lengths to achieve those same ADU values. If using separate RGB filters it's easiest to use one exposure for all three colours and choose an exposure that perhaps works for the 'dimmest' filter, probably Blue. Red and green will then be a little overexposed compared to the 'ideal' exposure but not enough to make any difference. It saves having to have separate darks for each colour. For OSC the same applies as you're 'stuck' with one exposure for all three colours. For a test image with no significant nebulosity and not satutated with stars the mean of the image will be close to the average sky background ADU for all three colours which should be fine to use. You can check sample pixels on your capture program to see the actual difference between RG and B pixels for more accuracy but it's not necessary to be spot on with ADU values as no two nights will have the same sky background darkness so a compromise needs to be reached that's fine for the 'average' night sky. These exposure calculations are really only of use for broadband imaging. For narrowband imaging the exposures required to reach these ADU values will be much longer than 10 or 20 minutes commonly used, so for NB it's best to expose for as long as you can get away with and accept that read noise will have some impact in your final image. Alan

Here's the chart for the ASI533 using ZWO's figures, and a link to download the Excel spreadsheet to make your own charts. The graphs are plotted from the data entered so you can quickly see if you've made an error. If you want a different swamping factor just change the factor number at the top of the column. To quickly enter all the e-/ADU gain values just enter the top value and the others will be calculated from that. ASI533, Sky Background ADU (SGL).xlsx Note that the camera offset contributes to the bulk of the ADU values calculated for most gain settings, as almost all of the bias ADU is from the offset. @900SL With regard to your initial question, I would say that for the ASI533 there's no point in using a camera gain setting below 100 (unity gain). Below unity gain you're effectively throwing away incoming photons. At gain 0 you need to receive 3 photons to register an increase of 1 ADU. If you receive 5 photons you still only register 1 ADU so you're throwing away 2 out of every 3 photons received. Also the read noise is higher and there's no real improvement in dynamic range. With the ASI 6200 or ASI 2600, gain 0 can be useful as I mentioned before, as it hasn't achieved unity gain at gain 0, so every photon received gives a corresponding increase in ADU. Here's the calculation for the ADUs shown in Excel format. 🙂 Alan

@900SL. No problem. I'll make the spreadsheet. I get all the info needed from the curves published by Zwo. I'll use the offset/bias figures you've quoted for an image you can download. I'll give a link to download the excel file too so you can make any changes you want to print your own sheet. The formula used is on the third line of the image I posted. Vlaiv provided the formula as an improvement on the one I originally used and he approved the latest spreadsheet contents too when I last posted it. 😊 The gain value used is the e-/ADU figire of course and not the camera gain in 0.1dB steps. I can use the data provided by @ONIKKINEN to provide another sheet using actual values to see how it compares to the published specs. Alan

@BrendanC I've produced Excel sheets for some cameras giving exposure times for specified read noise swamping factors like this. If you wish I can make one for the ASI533. You just need to input your mean bias ADU value ( and camera bit depth if not 16 bit) and optimun sky background ADU values are calculated. Swamping factor 5 is what I use, as vlaiv has recommended this in the past. With the calculator top right you can get an exposure time for a specified background ADU by inputing the values from a test exposure, or a previous sub you've taken if the sky darkness is similar. I also use zero gain when using luminance filters with the RASA 11 as at gain 100, it will swamp the read noise in 15 seconds, (in bortle 3). At gain 0, around 60 secs is required which is better to avoid 100s of subs. Alan