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I can't really comment on filter wheel from experience - I use filter drawer with my setup. I do know however that ASI1600 can get away with 1.25" filters if mounted fairly close to the sensor and I would choose filter wheel not based on size of filters but rather mechanical quality. You want your filter wheel to be precise so you don't have to take flats every time. This means that it should repeat exact position every time. Any small shift in filter position will move dust shadows and you won't be able to get good calibration. Flattener is something that you will need for larger sensors in order to have good stars all the way to the edge.

No, not a mistake. Many people that try (or have tried) such combination will find it works wonderfully. With choosing camera scope combo - it's not like on/off switch - one combo will work, while other won't. There is continuous range of performance, and sometimes when we talk about optimal setup - difference between it and "next best thing" will be more in theoretical domain than in practical. You will be hard pressed to tell the difference in SNR of let's say 5-10% in your data. It will be there, but for intention of image rendering it will be minimal if noticeable at all. 80mm scope and 1.54"/px sampling will need something like following conditions in order not to oversample: - 0.5" RMS guide error - rather difficult thing to achieve on HEQ5, it can be done but probably not consistently. It would involve modding the mount (belt, tripod/pier, saddle plate ....) and wind protection (or a calm night). - 1.5" FWHM seeing. This is something that you can in principle get on some nights almost everywhere. Getting such figures most of the time requires very good location (in terms of seeing). All this means that you will oversample a bit at 1.54"/px most of the time with 80mm scope on HEQ5, but like I said above, sampling rate is also not something that will either work or not work, it is continuum, meaning slight undersampling or slight oversampling will not be an issue that one will notice. If you have budget large enough, then do look at triplet scopes of 80mm range. While 80ED is fine scope, there are scopes out there that are optically better, will produce tighter stars and will get you into more comfortable zone in terms of sampling rate. For example Esprit 80, with 400mm FL and ASI1600 will give you 1.96"/px. There you go - probably better scope optically (and mechanically) and gives you about 2"/px.

You are correct in difference between cameras in terms of pixel resolution and FOV, but there is important BUT there - resolving power of scope and atmospheric conditions. 80mm aperture simply won't be able to resolve 1"/px under almost any circumstances (real ones that you might encounter - meaning HEQ5 mount and regular, even pristine skies). Even going for 1.54"/px is going to be a stretch in most circumstances. With 80mm scope you should really aim for around 2"/px. You can do 2"/px with ASI183 - just simply bin x2 your pixels and you will be there - question is, what would be the point? If you already have ASI1600 model and there is a scope that will give you 2"/px - I would go for that combination. In fact I have such combination and it works well. With larger sensor, you'll probably want a flattener as well.

That is quite normal. May people dread amp glow in cmos sensors but I think you have nothing to worry about, as long as it is repeatable (no huge variations between subsequent subs - and so far I think it is always the case). Even dark current in amp glow section is order of magnitude of read noise in most cases - again not something to worry too much about. Offset 15 is probably too low. Since you already did your bias subs, you can put them to good use - estimate if offset is too low. Do minimum stack on bias subs and then do stats on that resulting stack - if you get value of 4 that is not good. You want your bias values to all be above minimum value for camera. I think that minimum value that you can read off in single sub from your sensor is 4ADU (14 bit ADC, min value of 1 multiplied by 4 to fit 16bit format should be 4). IF you find that offset is too low - raise it but be aware that you will need to reshoot all your calibration subs for next session (this session you need to calibrate with subs that you have - with same offset of 15).

I found that dithering helps with this. Telegraph type noise is confined to pairs of pixels - at least that is the case with ASI1600. With dithering you spread them around in the same way as hot pixel - sigma clip deals with the rest.

Please do include both dark and flat calibration. CMOS sensors have pixel to pixel variation in QE as each pixel has its own amp so you will benefit from flat calibration even if you don't have any dust shadows on your optics. Don't need bias with CMOS sensors (it can even mess up your calibration). Use darks, flats and flat darks only.

Forgot to add - you'll need a coma corrector for 130PDS for AP - something that you can add later.

Yes, ST120 is going to be very nice wide field scope. In principle you can do AP with it, but there are several things that let it down in this regard - chromatic aberration being first, and sub standard focuser being second. If you plan attaching light weight camera onto it, then you can get away with stock focuser. CA can be controlled in variety of ways - using aperture masks to stop down aperture to 80mm or similar and use of specialized filters. It is not going to provide apo like shots, but it will be usable for AP. Having said all of that - there is better scope that is almost like ST120 in what it can offer and is much better at AP. Have a look at SW 130PDS. It has a bit more aperture 130mm vs 120mm, so it's better at light collecting and focal length is similar 650mm for 130PDS vs 600mm for ST120 - you won't loose much of wide field for additional 50mm of focal length. Focuser is much better / dual speed unit. Only drawbacks are collimation and diffraction spikes you will have in your images.

Should be able to do if such feature is implemented - it's really nothing special, subs are interpolated when alignment is performed, you can upsample RGB data in the process of resampling. If you are using software that does not have this feature - you can do it yourself. Take calibrated RGB subs and enlarge them x2 in some other software. Use nice resampling method like Lanczos or Spline resampling for that. Be careful not to use software that can't handle 32bit data - you want your subs to keep all the information.

Yes, binning will reduce pixel count in height and width. People do it with RGB data because of following: - Larger pixel surface (4 adjacent pixels joined) will gather more light. It enables you to achieve almost x2 SNR in same imaging time versus regular pixel size - Human eye/brain is less sensitive in variations of color than it is in variations of brightness (luminance) This enables you to get color data in less time and still have acceptable quality of image. Larger pixels means that you will probably be under sampling so you wont capture all the sharpness that you possibly could, but that is in color data - and eye/brain won't be bothered too much as most of sharpness that it can see will come from luminance data due to way our vision works.

Not sure if this is going to help, but I suspect that motorized rotator is not going to be easy thing to make - at least not by adapting simple mechanical one. In order to have relatively smooth rotation, mechanical rotators have certain slack between parts and also screws to tighten it to prevent any accidental rotation (due to gravity or cable snag). These screws remove any further slack when tightened (no rotation possible without use of excessive force) - it is a bit like focuser lock screw which is not used with motor focusers as they are expected to hold focuser in place by holding torque. Holding torque will hold rotator in place - prevent any accidental rotation same as with motor focusers, but in order for it to work and have no tilt - you need a design with some sort of ball bearings to allow for rotation - simple design like mechanical rotator will probably have tilt if you loosen up screws and leave them loose and rely on motor holding torque to stabilize rotator. Here is idea of mechanical side of things, fairly "simple design" - and you can adapt it to both worm drive or belt:

Already good advice given. Here are a few more tips that can help: - Note how LP changes over the course of the night. If you can - stay out till late in the night when most of the neighborhood goes to sleep. People tend to turn off the lights past some time in the evening / night. There will also be less traffic, so less headlights contribution to LP. Of course, try to match this with astronomical darkness - no point of staying up until morning hours if astronomical darkness lasts only until 2 or 3am. To that effect - begin observing after astronomical twilight has passed. - Make schedule of observing and wait until selected target is in best viewing position for the night - this means as high above horizon as it will reach (near zenith is the best) and also away from main LP. If you are not situated in center of LP (like city/town center) there will be side of the sky less affected by LP - wait for target to get there if possible. - Check forecast and mind transparency. If it is poor - don't expect too much. Poor transparency both attenuates light from target but also scatters LP more.

I would rather go for 90mm of aperture and 900mm focal length than a smaller scope, but second hand one is OTA - which means you will need to mount it somehow. If you already have suitable mount - I think it is better option. Main problem with such a cheap small refractor is going to be diagonal. Focuser is not going to be very good either (although usable) but there will be no difference between dob focuser and this one (in terms of quality). Diagonal is likely to be usable at best. Newtonians do have secondary mirror so no need for diagonal, and it is very likely that secondary is going to be of a better optical quality than cheap diagonal, so that is a plus for Newtonian. There is option that will bring best views in WL and solve diagonal in the same go - but it is expensive. It is herschel wedge - special kind of diagonal that passes only small percent of light (around 5% and it is equipped with additional neutral density filter). It gives sharpest WL views, but can only be used on refractors (which is probably better choice with such small apertures). When using this herschel wedge you don't need baader solar filter - it does all filtering you need (just make sure ND filter is included with wedge). But, like I've mentioned - it is fairly expensive piece of kit - it can cost more than scope it is being used on. I have this one and it is fairly good: https://www.firstlightoptics.com/solar-filters/lunt-white-light-herschelsolar-wedge.html You can couple it with polarizing filter, because light coming from the wedge is already polarized and additional polarization filter screwed on EP can be used to "tune" amount of light for comfortable viewing (and best contrast) - just rotate EP for desired light level before you tighten it in diagonal.

Projection setup might be better for any sort of measurement and "precision" sketching - you put a tracer paper and then you draw "to template". Regular observing is going to allow you to sketch, but in the same way one might be sketching the Moon and planets - there will be some skill involved there to get decent rendition. Although Heritage 76 is probably good basis for the cheapest WL setup, I'm not sure it would be my first choice. What you save on scope and filter, you will probably loose on eye pieces / barlows. In order to have decent view of the Sun, you will want to start with something like x60 power for full disk and go upwards for detail (you need something like x100 up to see granulation). With 300mm scope that means 5mm FL ep and "lower" (or addition of barlow). About same aperture (hence resolving power) will give you this scope: https://www.firstlightoptics.com/evostar/sky-watcher-mercury-707-az-telescope.html and it would be even better if you could find 3" F/13 or something like that for such work. Maybe see if you can get a second hand refractor with such specs (doubt you will find a new model with such specs that is going to be in "cheap" category).

To me, this "delayed" reaction points to error in radius calculations? Maybe things that we expected to have happened on both S2 and G1/2 approaches did happen but "further down the hole" - meaning that time dilatation of black hole - delayed consequences in our reference frame?

My guess is that it is this EP line: with a slightly different housing. Probably Chinese made EP branded under different brands. I think this line is probably the same (different only by housing and possibly QA / coatings some minor internal improvements): https://www.teleskop-express.de/shop/product_info.php/info/p4924_TS-Optics-Eyepiece-Expanse-17-mm-Wide-Angle-1-25-and-2-inch-connection.html Also look at Celestron Ultima LX As for FOV - 70 degrees in 17mm FL fits 1.25" format, so FOV won't change as you are effectively not using 2". 2" connection is there for convenience - if you have 2" diagonal it just adds a bit of stability for large EP and you don't have to put in 2"/1.25" adapter if you have other 2" EPs when exchanging them.

I guess this is latest theory and is backed up by above paper: https://www.newscientist.com/article/dn24886-natural-ball-lightning-probed-for-the-first-time/ Sand in soil gets vaporized, or rather carbon from leaves and other carbon sources steal oxygen from sand to form pure silicon that is vaporized that re-oxidizes and that makes it glow (according to article and lab tests in 2006).

Not sure, but this is interesting paper on the subject: http://depa.fquim.unam.mx/amyd/archivero/Articulo-fenomenos-tormentas-electricas_26310.pdf There is interesting observation in that paper, to quote: Now, in first video that I posted above, there is section "Ball lightning in the lab" where they show sparks and miniature "ball lightnings" that look like coming from welding machine - like a piece of metal burning really hot - maybe like Thermite mixture - which creates plasma bubble that bounces around when in contact with solid objects? Maybe ball lightning is similar thing when lightning strikes ground and there is sand and iron present - forms similar thing?

Disclaimer: I don't do DSLR AP, but understand what happens, so will try to explain. Let's first talk about what ISO is. ISO is in principle multiplicative constant. As such it does not impact your image in any way with regards to SNR - which is important thing in AP. If you have some sort of signal that is let's say 100 units, and associated noise is 10 units (photons / electrons, whatever), and you apply high iso - you will be multiplying with some number like 10, so resulting signal will be 1000 and noise will be 100. Signal to noise ratio remains the same. Image remains the same once you scale it to display range 0-255. So in principle nothing major happens with high / low ISO with regards to captured data. On the other hand, there are things that happen when you change your ISO settings - read noise depends on ISO, and usually low ISO has higher read noise, and higher ISO has lower read noise. This will have some importance later in discussion. Another thing that ISO does is change your effective full well capacity. Let's say you have 14 bit DSLR. This means that digital values produced by your camera can have values in range 0-16383 (integer values). Actual signal that pixels detect can and usually is higher than this. In order to map hole range that pixel can receive to limited range of 14 bits - you need to divide it with something. Let's say your actual full well capacity is 60000 electrons. You need to multiply that with 0.25 to get values in range of 0-15000. Such values fit 0-16383. But when you select higher ISO, you will be using only portion of your true full well capacity. Sometimes with very high ISO you might end up having less than 14bits effective full well capacity. For example if certain ISO has multiplicative constant of 2, then actual electron count from 0-8191 gets mapped to output of 0-16383, and you end up having smaller effective full well capacity. Now back to your question about blow out. Only thing that makes a difference between stacking a few longer subs vs many shorter subs (of the same total exposure) is read noise. Or to be precise, how "important" read noise is. There are a few sources of noise (shot, thermal, LP, read noise) and difference between few longer vs many shorter comes down to how "big" read noise is compared to other noise sources. Maybe best way to illustrate this is by using triangles, as noise adds as linearly independent vectors: If read noise is close in magnitude to other noise sources like LP noise this happens: Total noise is larger than both read noise and LP noise. But if read noise is far less in magnitude to some other noise source - in this case LP noise, than this happens: So difference that read noise makes gets minimal and there is almost no difference between few longer subs vs many short subs. With lower ISO you will effectively have larger full well capacity, and LP signal levels will not occupy significant portion of the range, so single sub will not look blown out, but lower ISO will have larger read noise - which means you need to again swamp your read noise with LP noise in order not to make difference. What all of this means is: yes you can change ISO but there won't be any significant improvement in stacking result. If you have high background LP signal at 90 seconds - just use those exposures - going longer simply won't produce better results.

Moon is excellent suggestion (as it is very bright and hard to miss), but in principle you need a fairly bright star and longer frame and focus exposure. When you have star light out of focus it will spread over larger surface and signal on each pixel will be very low - that is why you need long exposure, but principle is simple - you will get a large doughnut from a bright star - or very very large circle with soft edge from the moon. Make a turn of your focuser and see if doughnut / circle increase in size or decrease - go in direction of decreasing size until you end up in a single point for a star or sharp moon disc for the moon.

Planetary imaging is a fine balancing act - on one hand you want to go as short exposure as you can, but on the other hand you want to achieve the best SNR that you can. Short exposure brings you frozen seeing, but also increases number of good frames - seeing is changing moment to moment, and at those good moments you want to be at very high fps to record as many frames of good moment as you can. It also gives you more usable frames - if for example you shoot 30ms subs and seeing conditions change rapidly it can happen that out of those 30ms - 20ms was decent and 10ms was poor, with 10ms subs there is a chance that you have two good subs, but 30ms sub will be blurry. On the other hand short sub means less SNR per sub. This is bad in two ways - first is read noise. Every frame has one "dose" of read noise - more frames, more total read noise there is in the end. In ideal world there is planetary camera with 0 read noise. With such camera it makes no difference if you stack 1000 x 5ms for total of 5 seconds, or 100 of 50ms subs. Result will be the same. In our not so perfect world, planetary cameras have read noise and this read noise makes difference between a stack of 1000 x 5ms vs 100 x 50ms - first stack will have 1000 doses of read noise and second stack will have only 100 (total light and associated shot noise will be the same). This is the reason behind recommending very low read noise cameras for planetary imaging. Second reason is related to actual shot noise - shorter sub, less signal you will capture in that sub, although in the end stacking enough frames will get you total needed signal, you need to stack them first and that means that software that is stacking subs needs to have enough signal per sub to figure out how to stack each sub. When you do planetary stacking - you assign so called "alignment points" over the planet. Software uses this points, or rather part of image under those points (and in vicinity) to try to figure out where to move pixels between different subs to align them properly. Due to seeing successive frames will "wobble" and planetary features will shift randomly. Software examines alignment points - finds features under each alignment point in all frames, calculates mean position and then shifts pixels in all subs to this mean position. In order to be able to do that software needs each sub to have enough signal, or rather high enough SNR as noise in the image makes feature detection and alignment less precise. If software can't properly align alignment points (or features in that position) - it will produce blur due to stacking - which is a bad thing. You want your subs to have at least some signal for stacking software to work properly - that is why you can't go very short, unless you image the moon for example and there is plenty of light to produce enough signal with even very small exposures. This is also reason why it is bad to over sample when doing planetary imaging - you will spread signal over too many pixels and SNR will be poor - there will be trouble with alignment (and if you over sample you won't have any benefit of additional detail because scope is not able to produce it - it is aperture limited after all). All this means that you adjust your exposure to given seeing conditions - you need to lower your exposure until you effectively "freeze" the seeing, but no less than that as shorter subs will just have lower SNR and you want the best SNR that you can get.

I think that on this particular night, going for 10ms made a difference. Btw at what focal length are you recording? Using a barlow or native? I'm asking because you seem to drizzle images for some reason, but I think that SW Mak102 has F/12.75 - that is even a bit over critical sampling for ASI178, particularly in red part of spectrum. That means that you are getting all the detail that you possibly can with this pixel size - there is certainly no need to drizzle as it will lower your SNR and it won't improve things.

I would not be too much worried about that. 0.4' PA error will cause max of 0.1"/minute drift rate - that is something that can easily be guided out. What I am slightly worried about is this: I would expect less of measured backlash for friction drive and I wonder why is it so?

I've got one as well - what if complex plain is not "complex" at all - but just a two component vector that has addition and other operations defined in a slightly different way. Thinking in complex numbers produces that sort of feeling - and it's not proper number at all - it contains imaginary part!