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Computing heavily depends on QM effects now. Storage for example - look at video titled Boy and his atom to get the idea of how "deep down" electronic device companies go in search for more computing power and storage. No way to develop new microprocessor process without QM for example - https://en.wikipedia.org/wiki/3_nm_process

I think I figured it out - it uses two 90 degree prisms to do the focusing. Top prism is moving back and forth thus changing the focus position by twice it's movement

I was not aware that spotting scopes have internal lens. Would that not change focal length and hence magnification as well? I have 100mm Svbony spotting scope "on loan" from a friend. It's not so much of a loan as trying to get it in working order as it's missing eyepiece and some bits, so I'm employing 3d printing to sort out those things. I've made adapter to 17mm plossl - which works very good. I was hoping to adapt a zoom eyepiece to it, but most zooms seem to have Smyth lens or something and their focus position is not compatible as they can't be pushed in further than protective clear window (which probably holds nitrogen filling as well) stands in the way. In any case - I did not notice any magnification shift when refocusing.

Here is an interesting question I can't find answer to online (I guess I'm either bad at searching of people simply don't write on this subject). Let's for example use cheap Chinese spotting scope - like one from Svbony. Let the scope be 80mm with range of zoom of x20-x60. On the label it says - close focus 5.5meters, so I'll guess focus range from infinity down to 5.5 meters. A bit of simple math tells us that focal length of such scope is, if we assume 7-21mm zoom eyepiece to be FL of 420mm, or F/5.25 scope. It might even be F/6 instrument if we take 8-24mm eyepiece. In any case we have a range of focal lengths that we can work with and let's go with 420mm or 0.42m 1/focus_distance = 1/focal_length - 1/object_distance 1/focus_distance = 1/0.42 - 1/5.5 (for close focus or) 1/focus_distance = 1/0.42 - 1/infinity (for infinity focus) Second is easy - focus_distance = 420mm (as we would expect for lens with 420mm focal length) and first one is, If I'm not mistaken: 0.4547m or 454.7mm or about 34.7mm over original position. As far as I can tell - neither eyepiece nor objective lens move - yet spotter is able to accommodate at least 35mm of change of light path. How does it do that? Does it have a set of mirrors that change the distance?

Look at spot diagram for RASA8 to see where the lack of sharpness comes from. It has nothing to do with additional central obstruction (which impact will be negligible given other factors - it acts on order of magnitude smaller stuff - like for planetary where normal F/ratio is over F/10 not F/2). Small pixels used with RASA8 are a waste. Ideal pixel size for this scope is about 9-10um if I'm not mistaken. Consult spot diagram for details.

We don't use darks to reduce noise. That is common misconception. Darks are there to remove dark current. They even increase associated noise somewhat when applied. If we don't use matching darks we will not properly remove dark current. This as a result has wrong calibration (any value that we read of from image will be skewed) and also - flat calibration will fail because of residual dark signal that was not removed. Best way to ensure that we remove dark current is to match the temperature as dark current is temperature dependent. Yes, we can try dark scaling - but it is not guaranteed to work with every camera (or indeed with every set of data). We need "well behaved' sensor for it to work (not much messing in firmware and trying to optimize things or remove amp glow and such). Here is procedure: 1. we first need to remove any bias / offset that is common for both ligths and darks. For this to work we must have stable bias and exposure must be truly linear with exposure length - measured mean ADU values for dark frame must be straight line starting with bias and then moving on to longer subs 2. Once we remove bias we can take dark and use arbitrary starting scale factor (usually 1 or we apply the rule of ~6C doubling of dark current mentioned by @sharkmelley above). We apply that scaling factor to darks and do calibration of our data - meaning scaled dark removal and then flat calibration. 3. We take resulting sub and calculate its entropy (information, see here: https://en.wikipedia.org/wiki/Entropy_(information_theory) ). Since we will be using 32 bit floating point precision, it is useful to round pixel values to fixed point number of bits in order to be able to properly calculate entropy of the image (say 16-20 bits per choice) 4. We then adjust scaling factor using some search algorithm - like gradient descent type and go to step 3 until we find scale factor with least entropy level Rationale in this approach is that improperly calibrated image will have higher entropy level / more information then properly calibrated image because there will be additional things present in image - dust shadows, gradients from poor flats, amp glow, .... Of course, poor data can mess up this process - if we for example have wrong flats - algorithm will be thrown off as it will try to both compensate for dark current (correctly) and for poor flats (incorrectly) and will end up with mess.

I don't think that you'll need M90 extension tubes, but it might also mean that you'll need to counter sink the reducer further down the focuser tube - depending on what reduction factor you decide to go with Use this calculator to get rough idea: https://www.wilmslowastro.com/software/formulae.htm#FR_a Just a few pointers - CCDT67 has around 303mm of focal length. Working distance is about 10mm shorter than actual lens to sensor separation, so if you put sensor at ~91mm from M48 thread - you'll be at 101mm optical distance. That will give you factor of x0.67. Depending on sensor size you are using, this might be too much. People often choose to go with x0.72 - x0.75 reduction instead. For that you will need to use 1 - X / 303 = 0.75 so it will be X = ~76mm. This is optical distance, actual distance will be 66mm. In that case, focus won't move so much inwards - it will be only: -25mm (so one 25mm extension removed. But do keep in mind that if you have threaded connection with your focuser (you replaced stock focuser) - it will be difficult to reach focus even in this configuration as distance from front reducer thread to camera will be around 100mm. It is best to either sink whole lot into focuser tube (loosing threaded connection part) or if you have 2.5" focuser - do some fiddling with different adapters / threads.

Was just looking at that eyepiece today (9-27 version) Unfortunately - seller might not ship to Serbia (as per ebay notice) Anyone fancies the trouble of getting one and then reselling / posting it to me

There are couple of issues with your reasoning there. First - who says that something can't be made out of nothing? As far as we tell, with present "configuration" of our universe, general rule is that something can't be made out of nothing, but at the moment of creation - we don't really know or understand conditions and there is no reason to extend our current experience to that "region" of existence. Things are different enough that our rules of physics might not apply there. Maybe in those conditions quantum fluctuations lead to popping into existence more permanently then they do nowadays. Second - there is a good chance time popped into existence in the same time as space as two are related into single entity called space time (as far as we can tell - at least they appear to be connected). In that sense - there is no "prior" to popping into existence and rules of causality as we knot them need not apply. Way we think that cause predates consequence may not be correct in that case and there might not be a cause for consequence that is our universe. In any case - big bang does not say how things came into existence, nor it aims to explain that part. It starts some time after supposed popping into existence or some other event. It starts when things are bunched up at very high temperatures in what we might call dense "ball" of energy.

If you are yet to get the camera - it's better to go with camera that will match your current scope. You don't want to go overly small with your pixels to avoid binning. Binning is ok when doing solar or lunar (in particular if you do Ha, in which case - above x4-x5 rule changes to x3 rule as it uses longer wavelength of light with less resolution) because you have enough signal to swamp the read noise in short exposure. Read noise is dominant factor in lucky imaging. You want to freeze the seeing - which means very short exposures - like 5ms or there about. In such short exposure planets don't give too much light (unlike Moon and the Sun) so read noise becomes an issue. For this reason you want low read noise camera and you want to avoid binning (as it increases read noise with CMOS sensors).

No, seeing is for all intents and purposes "ignored" when doing lucky imaging. This is under assumption we are talking about lucky planetary imaging (which only makes sense). What determines best focal length is pixel size. In fact - not focal length but F/ratio. You want to be between x4 and x5 pixel size in micrometers with your F/ratio. Say you have 3.75um pixel size, then F/ratio to aim for is 4* 3.75 = 15, so F/15 and 5 * 3.75 = 18.75 so F/18.75

Laptop with SSD and SharpCap No, it is not worth the money, use manual focus (and learn how to focus while looking at live stream on your laptop) Makes no difference - use one that is easier for you / feels more comfortable.

Out of interest, what sort of evidence would you consider prove existence of Black Holes? There is so much evidence on them that I really can't see term "unproven" being used for their existence. We have detected gravitational waves from their merger. We have tracked objects gravitationally influenced by massive black hole in center of our galaxy, We have seen massive jets being ejected from some galaxies. We have even two images from radio telescopes of phenomena associated with black holes. What else must there be to "prove" their existence? Not sure what people have on Big Bang that's confusing them. I do think that there are some aspects of Big Bang cosmology that need further explanation (like inflation / inflaton field), but idea that stuff was very dense and was "condensed" at one point - is pretty much backed up by observational data. We have CMB, we have baryon acoustic oscillations, whole idea fits well with GR which we have rather good understanding of and bunch of evidence.

There is no such thing as underexpose in astrophotography. Overexposure is not a good thing because you loose information, but, again, overexposure is not the same thing as in daytime astrophotography and there is a good chance that some parts of image will be overexposed even in what we would normally consider proper exposure. With astrophotography we have very powerful tool at our disposal - which we don't usually use in daytime photography (in general it is best to "unlearn" all you know about photography when doing astrophotography as most if not all concepts from daytime photography are inapplicable and often wrong in astrophotography). This tool is called stacking. With daytime photography we take only a single exposure and as such - we might be concerned with under / over exposure. With stacking and astrophotography - we simply don't think in terms of under / over exposure. We control single exposure length in such way as to overcome read noise of our camera with some other noise source (often sky noise but can be thermal noise in DSLR / non cooled astro camera). Once you swamp the read noise - result after stacking won't be different no matter how long individual exposures are as long as total cumulative exposure is the same. We deal with over exposure by simply using shorter exposure and then using only parts of shorter exposure in places where we actually have pixel saturation. This is mostly cores of very bright stars, but can sometimes happen on cores of very bright DSOs - M31 Andromeda galaxy and M42 Orion Nebula being two prime candidates for this type of "core burnout".

What phone are you generally using for this? There is a chance that phone is not the best of tools for taking images like that. Most phones have small fast lens. Here, emphasis is on small diameter. If lens diameter is smaller then exit pupil, phone will act as aperture stop and it might render better image than it actually is for observer. Say you use iPhone 13, it has following specs: Primary: 12 MP sensor, 1.9µm pixels, 26 mm equivalent f/1.5-aperture lens, sensor shift OIS, Dual Pixel AF Ultra-wide: 12MP sensor, 13mm equivalent f/1.8-aperture lens, PDAF, 2cm macro Tele: 12 MP sensor, 77mm equivalent f/2.8-aperture lens, OIS You use primary camera. It has 26mm equivalent at F/1.5. Sensor is 12MP with 1.9um pixel size. Let's say that ratio of the sensor is 16x10 for sake of argument square root of(12MP / (16x10)) = 274px per 1 unit, so it will be 16 * 274 x 10 * 274 = 4384 x 2740px sensor It has diagonal of ~5170px and at 1.9um that is 9.8mm sensor size. That is about 43.2 / 9.8 = 4.4 crop factor, so 26mm equivalent lens will actually be 26 / 4.4 = 5.9mm lens. It has aperture ratio of F/1.5 so actual aperture size is 5.9mm / 1.5 = 3.9mm Any exit pupil recorded with this lens will be stopped down to 3.9mm exit pupil, so long focal length eyepieces that produce larger exit pupil will be rendered better then they are in reality.

And just like that (phrase that sounds familiar for some reason?) we jumped from focusing to this: https://en.wikipedia.org/wiki/B-theory_of_time

And that was before I even saw that you edited your post

Further you are from the axis of rotation - smaller angle for the same linear motion. So you can make fine adjustments with lever much more easily.

I'm not entirely sure you'd need dual speed focuser for telescope that slow. Here is a handy table: If MCT has focusing screw with standard pitch - say even 1mm pitch (but 0.75 or 0.6mm would be more realistic) - it would take half a turn of such focuser to move across critical focus zone at F/15

I'd go with classical Cassegrain. I have 102 Mak and I put it to test once on Jupiter against simple 100mm F/10 achromat and achromat pulled ahead despite having residual color. I expected Mak to perform just a tiny bit better than achro, but it was the other way around. This shows two things: - Skywatcher Maksutovs have some sample to sample variations of course, and it really depends how lucky you get. - That particular Maksutov design is a bit of a tradeoff. Maksutovs should really be F/15 or slower and ones by Skywatcher are Gregory Maksutov type. They have secondary aluminized spot on back of corrector plate and not separate mirror. This limits how well corrected particular scope can be - and they are a bit too fast at F/12. This tells me that design itself is probably capable of being better performer then these particular executions by Skywatcher. On the up side - they are affordable for what they offer.

That is tall order. Mount that will handle (hopefully happily) 10Kg of scope and track for 1000e. I'd consider one of two options: SkyTee2 + DIY stepper motors and a custom controller. I know people have adopted steppers to SkyTee2 because it is actually EQ5 inside (internals / worm gear are from EQ5) so motor kits for EQ5 fit, but I'd probably go fully DIY. Other would be to go with dob mount with tracking. You can get ready made dob that tracks and just swap the OTA - sell one that came with scope and use dob mount for tracking. Other is to DIY. Here you can DIY the whole thing. Probably best budget wise - it is just a question if you like the dob mount with 6" F/6 scope (a bit short - but not as short as F/5).

Is motorized mount mandatory? What would be the budget? I'm thinking either SkyTee2 on low budget end or Rowan AZ 75 / AZ 100 depending on how much you want to spend and if you want to have some margin for future upgrade payload wise. Motorized / goto versions, I'd look at AZ-EQ5-GT or AZ-EQ6-GT, again depending on budget and future weight requirements (and possibly weight of the mount itself). For budget tracking variant, I'd consider adding steppers to SkyTee2 in some sort of DIY alt/az configuration

Doesn't look like one - but it is one. It calibrates out though, so nothing to worry about - just use matching darks.

For very large dobs where observer must climb a ladder to observe - it is usually on the opposite side. Rationale being - less chance of accidental fall. We are more likely to go out of balance and fall if we "chase" the focuser rather than if it "presses" into us as we track the sky. We can lean forward but most people get uncomfortable when leaning back very quickly and there is more chance we will notice that we must change ladder position. On the ground - I guess there is more "viewing" time if we lean somewhat forward before we adjust our chair.

It is a tradeoff. Longer wavelengths are less disturbed by seeing. Longer wavelengths offer less resolving power (800nm will have only half of resolution of say 400nm as there is linear dependence on max resolution vs wavelength). Most sensors are less sensitive in longer wavelengths. Bandpass also plays a part. Wider filters are less sharp then narrow band ones (all else being equal).