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This is good example of how math was discovered rather than invented. If we invented certain imaginary unit, let's call it i with property that i^2 = -1 (i squared is equal to -1) - then we would also invent its properties, however, we found out that complex numbers - which are numbers that consist out of two parts - real part and imaginary part - follow the same set of rules as other numbers do. How come? Well rather simple really - real numbers that we discovered before are in fact a subset of complex numbers. Any real number is just complex number with imaginary part set to 0. If we were inventing things - we would only invent things that a) useful - which this one is not - because as you put it - in physical world it has no obvious meaning or b) have certain traits that suit us, but what are the odds that something that suits us perfectly fits with things that we already "invented", on such a deep level? What are the odds for example that this imaginary unit that we "invented" fits perfectly within this identity: That joins together 5 of what we could call fundamental constants - 0 which represents absence of things, 1 which represents singular (special state of existence - there are many plurals but only one singular ), base of natural logarithm, constant of circle and imaginary unit. If we invented i - we would need to invent above equation at the same time, at the time we were describing i and its properties (here is i, it's square is -1 and it fits above equation like so, and has all these other properties ....). Otherwise we are discovering that i that we just invented (and did not exist prior) fits something that we later discovered - but if we invented it just now - how could it possibly be part of something that we discovered later - it must have existed and been part of that equation all along - we did not invent it - we merely discovered it. I know this sounds confusing when I write it like that - but think of it - above equation was discovered much after i was defined to be what it is.

"Problem" that I'm seeing with this approach can be summarized in that old question: "Did we discover or invent math?". I personally think that we discovered rather than invented math, and as such, our formal mathematics is only one way to express rules of math - true underlying system of relationships. Similarly, cellular automata can be used to describe the same. There are number of such different approaches to the same thing. In programming we have imperative and declarative languages which are different ways to accomplish same thing - write down an algorithm or "rule" of how to solve particular problem. In some sense traditional/formal math can be thought as declarative language while cellular automata as imperative language. Physics laws further depend on mathematical formalism, and if you have some sort of math language - it is very easy for physical law "to emerge" from these set of rules - simply because set of rules describe mathematical thing and mathematical thing describes physics law. Question is - does system of rules that we observe produce only certain set of physics laws or does it produce vast landscape of possible physics laws - string theory has this issue if I'm not mistaken - it can be used to create almost any set of physical laws.

Biggest one that you can afford / carry / use ... More important than the size of telescope is dark sky. This is why people often say that tank full of gas is much more important than the size of the telescope. If you can drive away to remote dark location, then even something like 4"-5" will show you all the things you listed. Take 12" in white zone and you'll be disappointed with views. Another important thing is to learn how to observe - it is a skill and longer you observe - easier it is to see things. Eyepiece don't need to be expensive - nice set of BST StarGuiders will be all you really need. Even stock eyepieces that come with telescope will show you these targets nicely under good conditions.

Stars in third image: in focus ... Stars in first image: very out of focus Stars in second image: even more out of focus. In any case - you should not compare DSS score between different sets - within a set - it gives you some sense of how good frame is compared to other frames in that set.

Not related to object, but there is rule that covers it generally: Expose until sky background noise (light pollution noise) is significantly higher than read noise (meaning of significantly higher is open to interpretation here). That is rather general rule - but it works rather well for all use case scenarios. More general rule is - expose until any time dependent noise is significantly larger than read noise - most people use cooled cameras, so thermal noise is not going to be first to be significantly larger than read noise. Likewise, most people image faint targets - so target shot noise is not going to dominate read noise - but light pollution noise is ever present and for most people presents source of noise that will first swamp read noise. You want LP noise to be x3-5 larger than read noise - and you don't have to expose for longer.

Was reference to that professor saying that there is no single sentence that was reproduced correctly - a joke or it actually happened?

Well, this has been interesting. First part looks like it is just a pop science presentation with bunch of wrong views/interpretations. Middle part with that professor refusing their interview to be used with following explanation: "There is no single sentence in this account that has been reproduced correctly or is grammatically correct" does make one wonder why on earth are they spending half an hour of their virtual existence on this video. Luckily, last part actually holds some value and some very interesting ideas have been put forward.

FF/FR is most definitively cause of reflection. You can calculate total path of light to and from reflection by inspecting what diameter reflection is and taking into account F/ratio of telescope. If you do that, it is very likely that you'll find it is back side of reducer that is causing reflection. If it is matched FF/FR then I don' think it will be responsible for poor color correction.

Indeed, I expected to see less of it too. This one has CA on the level I would expect from 102ED model (one that uses FPL-51 glass) - not 102ED-R. What FF/FR are you using? Maybe try couple of subs without it to see what happens. I believe it is also responsible for reflection, but it could as well cause issues with CA. I'm no optical expert so I can't claim that, but I've seen that specific model of FF/FR is recommended for F/7 ED doublet by TS. Not sure why particular FF/FR would be required and if regular one would work as well - but it might be something to do with above CA levels?

Yes, the stars, or rather blue part of the spectrum. I highly doubt it is due to camera. It can be due to processing somewhat, but even then it needs to be in the data in order for processing to emphasize it. That is just too much blue bloat around stars. On the other hand, it is fast at F/7 for doublet scope even if it has FPL-53 glass. On the other hand TS in Germany placed this scope in their Photoline series - which clearly means it is meant for imaging. In any case, you might want to look at Astronomik L3 filter to try to see if it will reduce star bloat. It is UV/IR cut filter but cuts off a bit more on far ends of spectrum where telescope has the worst color correction. To give you idea of why I say that - this is image taken with very simple f/5 achromat and guide camera: That is attempt at Crescent nebular, and while image itself is very poor - it does show you level of bloat that you'll find in very cheap fast achromat of the same size. Telescope costing about x4, being slower and having exotic glass should not have the same issues with stars. While my image above is not really good, here is another one that I've found via google - credits go to SGL member here: you can see other work here:

Of course - this is just AFOV test - to see if it is as stated, but it has noting to do with how the eyepiece performs except to tell you how much of the sky you will see.

You can easily check AFOV of the eyepiece compared to another by looking thru it without a telescope - just hand held against white wall / ceiling. That way whole FOV will be white while field stop will be black - swapping between two eyepieces ( even holding against different eyes and swapping eye that is open) will give you idea of size of FOV compared to another eyepiece. Magnification will not play a part there as there is no object to be magnified. Take any plossl and compare the FOV size - if it's less than that - it is less than about 50-52 degrees.

What is primary interest? Is it planetary? If so, pixel size and pixel count as well as format of sensor - have absolutely no bearing on decision - main two parameters should be QE and read noise. If you plan on doing a bit of lunar as well - then you should take sensor size into account also - because it will take less panels to create full moon mosaic. For solar, things again change as for EEVA / DSO imaging. For last two - sensor size becomes dominant factor as it enables you to pair camera with much larger telescope and get larger aperture for same field of view (which also requires heavier mount, etc, so all things need to be considered there).

I don't think I'll be much of a help there. It's the first time I've ever heard of a "Digit" being used as unit for something and I don't know much about mV as a unit. I have an idea of what mV could be, but it is not "sensible" unit to compare to other units - it is "internal" measure - for Sony cameras, as far as I understand. Sony has developed some sort of sensitivity measurement protocol where they use their "standard" light source, their "standard" lens and use something like 1/30 or 1/60 exposure and then measure voltage from electrons gathered in a pixel. At least I think so. What we can do is try to figure out values from your table above. ASI178 has saturation of 945mV and 15000e FW, so we have 15000/945 = ~15.873 ASI224 has 1210mV and 19200e FW => 19200e/1210mV = ~15.868 ASI290 => 14600 / 913 = ~15.991 ASI183 => 15000 / 942 = ~15.924 I would say that most pixels have ~15.9 conversion factor between mV and e. As far as sensitivity goes, I'm not sure where you have your figures from, but here is for example screen grab of IMX178 sensor info (sensor in ASI178): found here: https://www.1stvision.com/cameras/sensor_specs/IMX178.pdf In any case, that value is not telling much. Here is why: and look at QE graph of ASI224: Green captures all the way up to 1000nm having significant peak (more than 50% of its max value) at 820nm. These wavelengths you won't be using in astrophotography unless you are doing IR imaging and using particular filter to capture only light above 800nm If we have F/5.6 lens and 1/30 exposure - both cameras should capture signal that is in relation to their pixel surface and their peak qe. for ASI178 this would be 2.4 * 2.4 * 0.81 /425 = ~0.011 for ASI224 this would be 3.75 * 3.75 * 0.8 (quoted value for peak QE is between 0.75 and 0.8) / 2350 = ~0.0048 It looks like ASI224 is twice as sensitive as ASI178 somehow, but what happens is: ASI 224 has twice the surface under green QE curve than one would expect from regular camera that covers about 500-600nm for green channel. Will this be useful for astro photography? if you use IR cut filter - no. Don't look at published results from Sony (and others) - they are OK if you want to use camera in both day and night surveillance applications or similar - then yes, it will be twice as sensitive. Btw - this is where partial answer to original question lies - surveillance sensors often need to capture large horizontal areas - and not much in vertical axis - hence those wide formats. Pixel size, peak QE, read noise - these are the things that you should compare. If camera has some "perks" like - ASI224 for IR imaging - that is a bonus if you plan to do that sort of thing.

I'm quite surprised with poor color correction for FPL-53 doublet.

Given that universe is all there is - I maintain that the size of universe is precisely 1.

Just an idea - universe will not end. If we accept that "there was no before big bang" in sense that "time came into being together with everything else in the big bang" so it's pointless to talk about before the big bang - similarly there will be no "after universe" - as such, if there is no after and it is pointless to talk about after - universe will not end. Very similar to falling into a black hole, isn't it? Nothing can really fall into a black hole - at least as far as we are concerned. If something was on a trajectory tending to cross event horizon - it will never reach it as far as we are concerned - as we will witness, it's time will run ever so slower and it's speed will decrease asymptotically. In fact it will tend to fade out of existence as all the light that bounces of it will be slowly red shifted and after a while we will stop seeing it in visible light and only detect its echo via radio waves. How about that?

Orion SkyQuest XT and Skywatcher 200p should be basically the same scope - different packing. Most of other brands also come from same factory - there are really two major manufacturers of mirrors for these scopes - Synta and GSO. There is a bit of difference in how rocker box works I think - different tension system, but use is just the same. You just place it on ground - point and look. There is not much to it really. That size dobsonian telescope offers one of the most comfortable observing positions. Only thing that you might find problematic is straight thru finder as you need to bend your neck quite a bit to locate objects near zenith. People often replace stock straight thru finder with right angled version. Otherwise, it will be very pleasant experience. You might wonder if looking "at the side" rather than "down the tube" will somehow confuse you, but I really never felt strange while using mine and never thought about it. I can see how this can confuse perhaps a small child, but I never heard anyone complaining about having issues with that. I observe seated with mine and one of the things that you might like to get is simple height adjustable chair like this one: or similar.

I'm not sure I can do anything with this data, as it has not stitched properly - not sure what software / workflow was used for stitching, but here is deep stretch of luminance: Maybe try first to see if you can get decent linear data. My advice would be to use following approach: 1. stack each panel separately 2. wipe background of each panel 3. align panels to form mosaic (but don't stitch them yet) 4. do linear fit of all panels to one baseline panel (maybe central) in overlapping region 5. Then "flatten" the image to get linear stitched mosaic

Mars will look small even at x150. Even in proper viewing conditions - meaning not looking from warm room thru several sheets of window glass (you probably have at least 2-3 sheets of glass there - anything but optical quality) in colder air outside, there will be very few details of mars visible if seeing is not great. Mars is tough target even for more experienced observers in comparison to other three targets you named - Moon, Jupiter and Saturn. Best improvements in planetary observing come from optimizing your viewing conditions. It is very important not to have anything between scope and target and to be at equilibrium to ambient temperature. This means that you need to take scope outside and wait for at least 20-30 minutes until scope cools down. That is like step number one - only once you've done that, you can look for other factors to improve the views (and there are several that you can do "right out of the box" - like not observing across bodies of water, or concrete - if you have park near by - go there to observe)

How do you know if particular feature is noise peak vs regular peak? Could you apply both on reference spectrum polluted with noise to see which one fares better? How about adaptive smoothing? I guess you extract spectrum from series of images that you probably stack or maybe you stack spectra extracted from multiple images. Could you use standard deviation of samples and intensity itself to estimate SNR at particular point and then apply smoothing based on SNR (lower SNR - more smoothing, better SNR less smoothing)?

I've found that following works rather good for star blend with nebulosity if one uses StarNet++ to do starless image: 1. Work with luminance only - leave color as is and do either LAB or ratio RGB transfer of color 2. With luminance - do linear stretch first - until you almost hit saturation in brightest parts of target. Don't worry about stars clipping at this point. You want dynamics of image as best spread over 16bit range so you don't loose anything over limited precision - this would not be necessary if StarNet++ worked in 32bit mode - but it does not 3. Produce starless image 4. Take image from step 2 and subtract starless image. This will give you only stars. Save that image In the end, take image from step 4 - pure stars and as top layer - set it to max (or brighten in PS if I'm not mistaken - you want it to show if it is brighter than background layer - and stars always are). I think you should be careful with setting background removal parameters as it tends to produce dark halos around bright objects. Here is 1 hour of M31 from very light polluted location (border of red/white zone) done with color camera and Luminance extracted: I scaled it down so you can easily see extent of the galaxy (and since it was taken with wide photo lens - it does not look nice as at native resolution ). Even with this short exposure it's starting to show its true extent - and it is well beyond even those stars that I marked in your image. It almost reaches from the top to the bottom of this image. Note that M32 is completely surrounded with faint glow from M31 - it is not "detached", and even M110 looks like it is joined to M31 by faint nebulosity. I'll see what I can do with your files - at least demonstrate starless approach if anything.

I would definitively buy this one as oil on canvas Seriously, it has some special quality - it really looks like a painting / abstract piece of art.

Telescope that will give you best views of everything you want to see in that price range is simply this one: https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-200p-dobsonian.html However, it does not have goto / tracking and it is quite large. It can be transported by small car, so that should not be much of a problem for visits to dark spots.

ASI224 is much better. ALCCD5L-IIc - the same as QHY5L-IIc has the same sensor and performance as ASI120mc - USB2.0 model ASI224 has USB3.0, greater sensitivity and lower read noise.