michael.h.f.wilkinson

I see the error in the forgetting the ADU count/e correction of 256. Note however that when talked about the 1.65 e read noise I said it was equivalent to 2.7225 thermal electrons, I did not say the thermal noise was anywhere near that high (in fact, I stated that that is very low indeed). However, you should not compare standard deviations of noise sources linearly, as standard deviations do not add linearly, variances do. The variance in the signal is ten times that of the read noise, so the read noise makes up only 10% of the variance in the signal. Using the value reported in the FITS header of 0.11447 I get a signal = variance = 29.3, or a standard deviation of 5.41, which includes read noise. Subtracting the variance of the read noise we get a sky variance of 26.58 or noise level of 5.16 . So yes, there is a degradation, but not by a third. Going to the example of the 1x 600s vs 10x 60s exposure, we get a noise of 16.39 or S/N of 16.22 in the first case and noise level of 17.12 and S/N of 15.53 in the latter, or just 10 % worse S/N, requiring 21 % more data (not ideal, but doable, nothing like the 140% more subs you mentioned). Doubling the exposure time doesn't do much, and increases issues like tracking errors, requiring me to dump a lot of subs, which has a much greater impact on the total amount of useful data captured. Regarding sky quality, the slightest haze immediately causes trouble, by reflecting city lights. On really good nights I get nice skies, but humidity or dust in the air totally wrecks the views. I need to get to dark sky sites, but curfew doesn't allow, and I need to get guiding sorted, but MS-Windows doesn't allow access to the COM port. I have a third mount I am setting up drivers for, but I haven't had a long enough spell of decent nights to want to waste any on experiments. I just set-up stuff that works reliably. I was thinking mid visual band, as used in lunar and planetary imaging, where anything between F/10 and F/12 is considered good for the ASI178 and ASI183. I do not want to vary sampling too much per wavelength. It's impractical. I do intend to see if my 0.6x reducer could be used with this sensor, as F/3.6 would be better. I tried once and got slightly eggy star shapes at the corners, so maybe the distance to the sensor is off. The thing is, I don't want to waste rare clear nights faffing arround experimenting with spacers. If i get a stirng of clear nights, i might try this out.

Thanks! The concentric rings are the results of different halos through different filters, combined with a lot of stretching. I must remove the stars before stretching, I suppose. I need to tackle those. What I did yesterday was first do a stint in H-alpha before it was perfectly dark, then switch to O-III as the moon had not yet risen, and the moment the moon was high enough to be a nuisance switch back to H-alpha. I was thinking of something similar tonight, as the moon rises later. A bit of a moot point now, given clouds have appeared, and show no sign of buzzing off. Maybe I will get a chance tomorrow. We will see

I did some calculations @vlaiv, and I do not think you are right. I am looking strictly at the noise in terms of electrons, so before any stretching by the ADC. The amplification by the gain setting does not alter the ratios of the noise contributions, it is just a linear multiplier. The read noise of 1.65 electrons corresponds to the noise caused by 2.7225 thermal electrons (using Poissonian noise statistics). The darkest sub, calibrated for dark current and flat-fielded has a background of about 4100 ADU counts (also without flats), or roughly 256 electrons (using your division by 16). The latter (which includes the read noise) has a Poissonian noise contribution of 16, or ten times the read noise. If we subtract the variance due to read noise from the total variance, and take the square root of the result, the photon noise and dark current (truly low) is 15.915. Thus read noise is negligible. Let us stick with the 256 electron/min signal. If we take 1 600s sub, we have a total noise of the sqrt(2560 +2.7225)=50.62 which means S/N of 50.57, whereas if we take 10 60s subs we have sqrt(2560 + 10x2.7225)=50.86 yielding S/N = 50.33. Regarding the sampling, Nyquist suggests the 2.4 micron pixels are optimal at F/12, so this 80 mm is undersampling by a factor 2 at F/6, and by 2.5 at F/4.8.

I have used the TMB Paragon 40 mm (of which the Aero is a clone), and that was fine in an F/6 APO triplet. The 40 mm is reported to be the best of the bunch, but sadly no longer available. If you can get your hands on the MaxVision 34 mm 68 deg, that would be a good option (same optics as ES)

Haven't done so yet, may do so in the future. Key issue here is that this mount carrying the lighter scope is an EQ3-2 without goto system (it does have an ST-4 guide port) for which I cannot find any ASCOM driver. The GP-DX mount has an RS232 interface for which I have a USB-RS232 cable, and for which drivers have been installed, but Windows 10 does not allow ASCOM to use the COM port. Permission settings are nowhere to be found. Thus, for the time being, I am stuck with tracking. Sometimes I get polar alignment close enough I can go to 120s, but beyond is unknown territory for now.

Sky background completely dominates the read noise and dark current here, even in narrowband (they are 12 nm filters, BTW), especially around full moon.

The 600D is an upgrade of the 550D, but for astrophotography the main thing is the sensor, which in this case is the same. In a modded version, the filter in front of the sensor is replaced or removed, gaining a factor of three in sensitivity in H-alpha.

I was working at F/4.8, using my APM 80mm F/6 with focal reducer. Given I haven't got the mount on speaking terms with the computer, I just use tracking, and this limits me to 60 s subs. I just stack loads of them (this is only 3 hours of H-alpha and 2 of O-III). I use a fairly high gain (300) which lowers readout noise, but of course reduces dynamic range. I am thinking of using 2x2 binning on the O-III as it is so faint. I hope to grab another 3 hours total tonight. My main question is how to use that time to optimally improve the image in the short term. Do I go all-out for one of the bands, or do I split the time between them? Would adding S-II help, or even just RGB (2x2 binned) for an hour each to get the star colours right. Of course I want to gather a wagonload of data in all bands, but the question is where to start.

I have the 550D (modded) which has the same sensor as the 600D. It has been quite a stalwart performer these last years, and only recently have I switched to a cooled mono CMOS camera. I still use the 550D for its larger sensor. Here is an example that an unmodded camera should probably (roughly) equal, as it is a galaxy. The modification shows up best on emission nebulae like this one

Managed to get roughly an hour of usable H-alpha, and just over 2 hours of O-III on the Jellyfish, and combined this with the 2 hours 2 minutes of H-alpha of the 29th. Stacked and combined the lot in APP, and boy, is that O-III faint (not that H-alpha is that bright). I really should get data from a darker site. Still not totally unhappy with the result after some tweaks in Gimp Much more data is needed. Questions for tonight (forecast to be clear again): should I try for more O-III, or beef up the H-alpha signal first? Is there any point in going for S-II?

And we're off Faintest hint of Jellyfish to be seen

Up and running, just about to finish shooting a new dark library at -10°C, and hoping to get at least one more hour of H-alpha data and 2 hours of O-III on the Jellyfish Nebula, to add to yesterday's 2 hours of H-alpha.

I have just spotted those with my Coronado SolarMax-II 60. The top one on the northwestern limb is absolutely huge

That is amazing!

I agree that no 80 mm is going to best a 127mm mak-cas on planets. Even my 6" Schmidt-Newton is way better on the moon and planets than my 80 APO triplet, and that is not primarily a planetary scope. A long focal length achromat is not going to best a good quality apo or ED scope with a faster focal ratio in my experience (although they can certainly come very close or perhaps even equal them). Especially in imaging, aperture is king on planets. Regarding cool-down time: store the scope in an unheated room or garage, and it will reach ambient temperature much quicker. Also, the Schmidt corrector plate in my Celestron C8 is way thinner than the meniscus lens of the 180mm Mak, which means the tube cools down a lot faster (but also dews up faster, so dew bands are often needed). It also means the OTA is much lighter which is nice when setting up, and requires less from the performance of your mount. This is Jupiter with the C8 This is with the 80mm

Got 2 hours 2 minutes on the Jellyfish Nebula (IC 443) with my APM 80 mm F/6 , Tele-Vue TRF2008 0.8x reducer, ASI183MM-Pro and Astronomik 12 nm H-alpha filter. Stacked in APP, quick stretch in Gimp. Needs more data (perhaps also O-III), and some suppression of the halo around Propus Still, pretty pleased how this turned out

I much prefer narrow-band imaging in moonlight, especially H-alpha, as moonlight doesn't contain much, because of the strong absorption line in sunlight. Backgrounds become very dark indeed.

Gathering H-alpha data on IC 443, the Jellyfish Nebula, with the APM 80 mm F/6 triplet, 0.8x focal reducer, and ASI183MM-Pro

I am going for the Jellyfish tonight and tomorrow night. I am not going after galaxies with a full moon. H-alpha should be doable, perhaps O-III, but I will see how that goes with a full moon. H-alpha on the Flaming Star Nebula works well too

I much prefer the result without filters, as reflection components and dust are filtered out too much, although with a full moon it may be needed. On the same camera, with loads more exposure (7 h 11.5 min) I get this or with unsharp masking

I have been using the Optolong L-eXtreme filter at F/4.8 and used 30s subs on my Canon EOS 550D on M42 without issue. I did find the neighbouring reflection nebulae and reflection components in M42 itself were severely attenuated, so stopped after a few minutes of imaging, and switched to another target. Here is the resulting stack of 6 subs: The core isn't blown out, so 30s works, but you could use shorter subs if you like.

Fo rme it is FireCapture and AS!3 for capture and stacking (sometimes using PIPP to preprocess the stack before AS!3), For planets Registax 6 works best, but for lunar and solar I prefer ImPPG deconvolution and sharpening

Nice shot. ICE is an excellent tool for lunar mosaics. You don't actually need to get so much black area around the moon, using the auto-complete function the program readily adds black bits to the background as needed. That saves quite a bit of capture time too, especially if you do take 500-1000 frames per to stack for each sub (240 GB data for a whole moon, but stacking can be done in AS13 overnight in batch mode).

I don't quite get your point. The initial question was about full-disk imaging without the need for mosaics. Focal ratio in imaging planets, moon, or sun is mainly of importance in selecting pixel size. The ASI178MM and ASI183MM, with their small pixels, work best at a focal ratio between F/10 and F/12, so the LS35 and LS40 would work optimally out of the box. The LS60 will allow full disk imaging with the ASI178MM (just), but you lose some detail (undersampling). You would need a Barlow to reach full resolution, but then you need a bigger chip for full disk.

I could get full-disk images with the little LS35 I had with the bigger sensors, (actually, the ASI178MM would do that easily, at a very good resolution) I made the mosaics with the LS35THa way back then because I was using a much smaller sensor (using a DMK21), so to get sufficient resolution, this was needed. An LS60 would be fine on modern, bigger sensors. Currently, if I barlowed an LS60 with a 1.5x Barlow I would get the whole disk on the sensor of an ASI183MM. The reason I do mosiacs with the 80mm is purely because that system is more Quark like, has a narrower FOV and operates at F/27 or so, and requires larger pixels, so the ASI174MM is best.