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Yes, sorry, my bad All correct except one thing - bin x3 will give you x3 improvement in SNR - not x2 which equates to x9 imaging time and not x4. SNR improvement is related to imaging time by square root function, so x4 imaging time (or x4 number of subs) - gives you x2 SNR improvement, while x9 imaging time gives you x3 SNR improvement. Since you are binning x3 (joining 9 pixels - which is equal to stacking x9 subs or imaging for x9 longer) - you get only x3 improvement in SNR - or rather, SNR improvement is equal to bin factor. I know this fear exists with people - but that is just because people don't fully understand blur / resolution part of astronomical imaging. Resolution is not there to begin with. If bin x3 is proper sampling and you wonder what you've lost over having 6000x4000 instead of 2000x1333 - answer is noting. If you want to have 6000x4000 image for say printing purposes or whatever - just take 2000x1333 image and upscale it to 6000x4000. Result will be the same as if you've shot 6000x4000 under original conditions.

No, you are quite right - binning does not change FOV. One of things that focal length impacts is of course FOV, but I commented that which you quoted coming from purely sampling rate perspective under assumption that targets you want to image will fit the FOV. Sampling rate is function of pixel size and focal length. If we keep focal length the same and increase pixel size by factor of x2 - we get the same thing as halving focal length and keeping pixel size the same - in terms of "/px or sampling rate. Similarly if we increase pixel size by x3 (binning x3) we get the same effect as using 1/3 of FL and keeping pixel size the same. 1600 / 3 is roughly 500mm (or 533.333 to be precise) hence my assertion. RC will be faster than your current setup even if you want to quadruple FOV (double it in each height and width). When we did "speed" calculations we concluded that RC + x3 binning is about x6 times faster than your current setup. If you image target for 6h with your current setup - equivalent will be 1h with RC. If the target does not fit ~ 50' x 33' that 8" RC gives you natively, you can still do 2x2 mosaic for example - that will give you ~ 1° 40' x 1° 06' FOV (probably a bit less due to overlap needed to make mosaic but still 1.5 x 1 degrees) and if you image each panel for 1h (giving you same quality as current setup in 6h) - you will end up with total of 4h of imaging.

You can already do this with different tools that do PE Analysis and PEC curves - and they all have incorporated filters to remove high frequency motion to combat the seeing. Problem is - this high frequency motion can also come from mount roughness - and there is no way of telling as it will be masked by seeing fluctuations. It is really tug of war between exposure length which averages seeing effects and loss of high frequency detail. It is similar to guiding. I use 4s to 8s exposures to average the seeing - and it works, but I have no idea how my mount performs in those 4-8s. Is it smooth running or has some sort of vibrations?

It can but then you have seeing and weather to contend with. I wanted to see if there is "lab" method that does not require certain time of day (or night rather) and is not subject to seeing noise.

It does not really need to be that expensive. I would personally go for something like 8" RC + x3 binning - for very nice working resolution of ~1.4"/px. Speed wise, if we apply formula that you posted, we get: 203^2 * (3 * 3.76 * 206.3/ 1624 )^2 = ~84600 (1600mm FL and 203mm aperture, pixel size is x3 3.76 as we bin x3). Even if we account for massive central obstruction - things don't change much. This system will be x4 faster than most listed and costs fraction of the price of most of them. Speed of system plays only a part in total imaging speed. Light pollution is major factor to consider. I did some calculations and loosing just 2 magnitudes of sky brightness - like going from SQM18 down to SQM20 is equivalent to ~x6 speed increase! If we have dark skies - then speed of system is not that big of a deal, but for someone imaging from city - it is very important as they are already at disadvantage. By the way - there are a few other factors that are major contributors to speed equation, that most people don't consider. Take for example target position and transparency. We might not think much of those, but let's run some numbers. Say we have target that passes thru zenith as some point in the year but we are impatient and want to image it early (or don't want to wait for next year) and decide to image it at 60 degrees above horizon. We also don't want to wait for very transparent skies (say AOD 500nm of 0.1 and instead image at 0.3). How much speed did we loose? Instead of imaging thru 1 air mass - we image thru ~1.1547 air masses. We loose 0.16 magnitudes per air mass so we have 0.1547 * 0.16 = ~0.02475 magnitudes loss due to angle alone. Using AOD (aerosol optical depth) of 0.3 instead of 0.1 we have 0.2 magnitudes of AOD - we multiply with 1.086 to convert to stellar magnitudes so that is 0.2172. We add two together and get 0.24195 of magnitudes fainter target. If we convert that into intensity we get ~0.8, or only 80% of light from target reached us instead of 100% - reciprocal of that is ~1.25, or we need 25% more time at best to get same SNR. So imaging in right conditions is like swapping FRA400 with ~24387 telescope (none of ones you listed manages that)

First of all, I would not think of terms of focal length but rather working resolution / pixel scale. Mount has no idea what is the focal length of telescope that it is carrying nor it cares - it will behave the same (if weight and size of scope is the same). Second thing - I would not think of mount as being hard limiting factor for certain resolution, but I would rather think of mount being able to do two things: 1) support the weight of the scope and accessories with certain ease (overloading mount just makes second point worse) 2) being able to be guided to certain precision With respect to first point EQ6 is step up over HEQ5 class mount, but with respect to second point - not really. Given certain care for the mount (tuning and modding) - both of them are capable of guiding down to 0.5" RMS. Next tier up, mount wise would be something like iOptron CEM 120 (maybe we can even consider CEM70 to be step up over EQ6/HEQ5 in both points, but I'm not 100% certain of this - not sure if it will reliably guide below 0.5" RMS most of the time). Following tier for me would be mounts like Mesu 200. It does not need be that bulky or expensive - there is mount that is same tier but is less weight / cost - take a look at E.fric for example: http://www.geminitelescope.com/efric-friction-drive-mount-german-equatorial/ With that last tier you basically remove mount from the equation, or at least that second point. You get mechanical side of things - tracking / guiding as well as it can get. In any case - these could be steps up the mount ladder: 1) 1" and above RMS (EQ3 / EQ5 type mounts) 2) ~0.8" RMS - this is common for stock EQ6 and HEQ5 mounts 3) down to 0.5" RMS - this can be done on tuned EQ6 / HEQ5 mount 4) ~0.4" RMS - I think iOptron CEM120 should be capable of this (version without encoders - I'm not considering encoders in this) 5) ~0.2 - 0.3" RMS - this is really top tier for mounts - this is where guiding is good enough - it stops being determining factor for most part You have idea of what your current RMS is and this will help you decide what would be step up for you (I'm at point 3) with my HEQ5 that is tuned and modded, and hope to jump to number 5) at some future time). Yes, that is what speed of optical system is in nutshell. How much effective aperture you have (surface) to capture photons and how much you spread those captured photons (surface of pixel). F/ratio is good measure of speed if you keep pixel size constant. This means F/7 scope will be slower than F/5 scope in that case. However, F/ratio is not general measure of speed. This is because we don't need to keep pixels at constant size. We can use different camera, or we can utilize binning. When we do that - things can change drastically. Take for example 4" F/10 refractor vs 4" F/5 refractor. F/10 is way slower, right? "No one in their right mind would image at such slow speed" , right? Just for a moment consider this. Both scopes have exactly the same aperture size, so they gather same number of photons - same amount of light for given time. Neither is "faster" in that respect. F/10 will have longer focal length and will spread light over more pixels. Each pixel will thus have less photons and signal goes down. This is why it's slower, but what if we make pixels twice as big (simple as bin x2)? Focal length is twice as big in F/10 versus F/5 and if pixels are twice as big - then effective pixel size remains the same. Suddenly F/10 scope is as fast as F/5 scope - it gathers same amount of light and it spreads that light over same number of pixels. Most people would not image with 4" F/5 achromatic refractor due to chromatic aberration, but never even consider using 4" F/10 achromat for imaging - believing it is "too slow" - although it has decent color correction (not perfect). In fact F/10 achromat with 80mm aperture mask and x0.67 reducer is cheaper than SW ED80, equally good for imaging and more versatile scope (but I'm starting to digress here). So yes, just because scope has larger aperture - it does not mean setup with such scope will be faster (as scope is only a part of setup). Similarly - just because scope has "fast" F/ratio - it does not mean setup with such scope will be faster than one with slower scope. We often don't consider binning and long focal length because we are afraid of loosing FOV or having too few pixels in our image - but in reality, majority of target out there are rather small. This is why I asked you in the beginning what do you expect. Diffuse nebulae (Ha regions, dark nebulae and alike) in Milky way are among largest targets and require wider FOV, but if you want to do general imaging - most targets span only dozen or so arc minutes - x5-x6 less than one degree, or about 1/2-1/3 of a full moon. Even target like M13 is less than a degree in FOV. APS-C sized sensor will cover one degree with something like 1200-1300mm of focal length.

This? It is a "seam" - over extrusion after priming the nozzle for new layer. I'm using SuperSlicer and there is a setting on where to place those seams. There are several options - one of which is "Aligned". It places layer beginning always in the same place and that creates a seam. If you want to avoid such feature in your print - choose random option. It will spread this beginning in different places and instead of single seam you'll have odd bump here and there.

Before getting any new equipment, I would revisit this bit. How far away are you driving and where? Can you find your favorite spot on this map: https://www.lightpollutionmap.info And what is the reading on it? 5-6" of aperture is quite plenty under really dark skies - it will show you hundreds of objects if you get dark adapted properly. Find a spot on above map that is green or at least green/yellow transition (SQM > 21.3-21.4) and see what can be seen from such location. Don't forget to get properly dark adapted.

With device for auto bed level - like probe attached next to print head - z offset is how you control things. ABL device always determines absolute bed position regardless of how you level it (regular z end stop is not used any more). There is some distance between tip of ABL probe and where you want your nozzle to be once print starts. This will determine distance between nozzle and bed and therefore thickness of first layer depending on amount of filament extruded.

I tweak it after flow calibration for example. Granted, very new to all of this, but I did have to do multiple flow calibrations to date. Once because I just got the printer, next time because I changed position of filament spool and changed tubing (much smoother extruder movement after that). Third time because I messed up calculations - I measured 1.1 flow multiplier instead of 0.9 (wrong direction for those 10%). I guess, that using different filament will require similar tuning to be done as well. As will changing the nozzle once this one needs changing, or perhaps when I upgrade to bi metal head break because I want to print some ASA and so on. It is not day to day activity but it happens ...

I guess that this depends on quality of printer itself. For something that is not of very high quality, constant thermal cycling will quickly throw things out of whack. I've found that bed level changes by couple tens of microns between room temperature and 60C that I use for PLA.

I've found auto bed leveling to be very very very useful feature (I'd call it essential upgrade). It helped me diagnose issues with z-axis. If you can have repeatable measurements and somewhat warped bed - then you can create mesh and see what is down to tilt (x axis gantry tilting due to z-axis issues) and what is down to warping of the bed. It also helps a lot with z-offset and getting that first layer just right. I still do manual bed tramming - and it helps with that as well - it checks all corners and reports measured heights / offsets - adjusting wheels after that is really easy - you get visual feedback on how much each needs to be adjusted.

It is, but it is apparently stopped down internally due to secondary size / and or / baffling.

That part is down to display device rather than sampling rate. When image is properly sampled, one still needs to match resolving of their eyes as well as display device pixel pitch and viewing distance. Similarly - over sampled image can look rather sharp when viewed from a distance. Proper sampling is just ensuring that minimum number of pixels (or rather sampling points - better to think of it that way) is used to record all information needed. This helps with SNR and in turn that helps with sharpening as we need good SNR in order to process and sharpen data properly. I can make over sampled image look good - just by simply moving away twice the distance to my display device. For example - I use computer screen that has 92ppi (1920x1080 resolution on 24inch computer screen - that is ~2202 pixels on diagonal for 24 inch diagonal 2202 / 24 = 91.75ppi). That makes pixel ~0.246mm in size 20/20 vision is resolving about 1 minute of arc. If I'm 80cm away from my computer screen - I perfectly match pixel size to minimum resolving size of good vision (I actually sit a bit closer at something like 60-70cm). In above conditions, viewing at 1.5m away, overs sampled image will look similarly sharp as correctly sampled image at optimum viewing distance (of ~80cm). People viewing on mobile devices will have different experience as pixel pitch on those devices is quite different - often going up to 400-500ppi, and older people have trouble focusing as close as 20-30cm, so often hold their devices further away - which makes image at 100% on such device that is x2 over sampled - just right.

But also seriously sharp and detailed when you resample it to proper size.

That really depends on flattener used with it and spot diagram. 120mm of aperture can resolve something like 1.5"/px under right conditions - for example, in 1.5" seeing and 0.7" RMS guiding (good seeing and something HEQ5 should be able to achieve on regular bases, at least tuned version) - it hits 1.5"/px. It has 840mm of FL - which makes it operate on 0.92"/px when using regular debayering (and I would advise against this) - or 1.84"/px when using super pixel debayering or split debayering which is ok. Here is an example of what Esprit 120 can achieve as close up:

Sharper is closer but the problem is that people don't really think this way. We think of being closer in terms of FOV, right? Above image of M13 is not very close in, right? How about this image: That is close in, right? Same image. It was taken with 80mm scope. Sampling rate is 2"/px - same as your image. When it is zoomed in 100% do you feel it is soft and too much zoomed in by looking at the size of stars? I think it has good sharpness - and this allows for it to be cropped and looking much "closer in".

Well, yes. I often advocate at least 6" of aperture in order to push down to 1.5"/px and 8" for going below that value. However, given above spot diagram - I think that you will see a difference with 107mm scope. Not because of aperture size - but because of better looking spot diagram. First thing to note is that spot diagrams are given in micro meters and not arc seconds. Here longer focal length gives a bonus because it makes error in micrometers smaller in arc seconds (same thing as being closer in with longer FL - but in opposite direction). ~4.9um RMS spot diagram on axis for FRA400 is really 2.53" RMS ~3.16um RMS spot diagram on axis for 107PHQ translates into 0.87" RMS So spot diagram alone is x2.9 times smaller. That will improve things as far as detail goes. Mind you - adding focal reducer will most likely skew spot diagram and make RMS bigger again. I would use it at native FL. This won't really get you closer in to your targets, but it will get you sharpness. Given that you use OSC camera, I would do super pixel debayer and effective resolution would then be 2.07"/px - but I think it would be "true 2"/px".

It is not easy to summarize the differences. I can give it a go, but I'm afraid it will be all but "summarized" - in same conditions 107mm of aperture has potential to out resolve 72mm of aperture. How much? That really depends on other conditions as these don't add up linearly. I'll give you few examples (good seeing, excellent mount, then medium conditions and poor conditions). Mind you - this is for diffraction limited optics (we need to discuss in some detail what I mean by this). In 1.5" FWHM seeing and 0.5" RMS guide error 72mm aperture will produce 2.46" FWHM which corresponds to 1.54"/px 107mm aperture will produce 2.17" FWHM which corresponds to 1.36"/px In 2" FWHM seeing and 1" RMS guide error 72mm aperture will produce 3.45" FWHM which corresponds to 2.16"/px 107mm aperture will produce 3.26" FWHM which corresponds to 2.04"/px In 3" FWHM seeing and 1.5" RMS guide error 72mm aperture will produce 4.89" FWHM (3.05"/px) 107mm aperture will produce 4.75" FWHM ------------------------------------------- 72mm aperture performs 13.36% worse, 5.83% worse and 2.95% worse with respect to FWHM size depending on conditions (from best to worst). If you want to really take advantage of larger scope - you need to have good mount and good skies and difference will be significant. Another thing to notice is that improvement in sharpness is not proportional to aperture size - double the aperture and you won't get double the resolution, so even 150mm aperture wont help much in poor conditions. Mind you - above are theoretical values for diffraction limited aperture. Most scopes that we use for imaging are not diffraction limited! Most of them will in fact produce more blurred image. Primary optics is almost always diffraction limited in center, but we almost always use correctors of some sort - like coma corrector, field flattener, focal reducer - you name it. These often make optics perform under diffraction limit. Take look at Askar FRA400 spot diagram: RMS radius is 4.873um in center of the field and growing as you move away from center. As a comparison - RMS of Airy disk of 0.662" for 72mm of aperture, which at 400mm focal length gives 1.28um RMS (0.516"/um for 400mm). That is x3.8 larger Airy disk because you are using quintuplet astrograph instead of regular refractor. Note that in average conditions we calculated expected FWHM of ~3.5" for diffraction limited optics - and we measured about 6.75" FWHM in your image. How come that we have such huge difference? That is down to having optics that is not diffraction limited. If I do another calculation for same parameters (2" FWHM seeing and 1" RMS guiding) but this time instead of 72mm I use 19mm of aperture - which gives x3.8 larger airy disk - I get expected FWHM to be: 6.66" FWHM star profile - which matches what we measured in your image. What does this mean for 107mm vs 72mm comparison? Well, we can't really tell until we see spot diagram of 107PHQ and we run some calculations. Will there be some improvement - I think so. Probably most improvement will come from larger aperture coupled with very good field flattener with excellent spot diagram. Alternative is to use telescope with longer focal length that has flat field without additional corrector and already good spot diagram and to bin those to get to your target resolution.

Under sampling is never a problem. Over sampling - it's not a problem in itself if you accept two things: 1. You will spend more time imaging to get the same quality image 2. When viewed at 100% zoom - your image will not look as sharp Luckily - you can choose to correct both of these things after you are done imaging. With CMOS sensors there is no difference between binning in firmware and binning in software and you can choose to bin in software later on.

Above design did not work very good in PLA - material is not flexible enough. It can easily be shut but can't be released that easily (need to wedge little screw driver there to release it). I had some clearance issues (needed 0.4mm clearance and still some parts fused together and I had to apply the force to get the hinge working) - will need to re calibrate flow and still waiting for that z-axis upgrade to arrive. There will be a design change - instead of using snap mechanism, I'll put in thread and thumb screw for securing the clip in place.

AstroImageJ gives quite different results. Something else seems to be off Average FWHM seems to be around 3.5-3.6px. FITS header of that file is also very strange - it gives: Pixel size seems to be reported correctly, but focal length is set to 749mm and hence pixel scale is 1.0356"/px? Do you plate solve or did you manually enter 750mm FL for some reason? Is this image from that 400mm scope? If image is from 400mm and all else is correct apart from wrong FL reported - then your FWHM values are about ~6.75", which means that you should be sampling at about ~4.2"/px or image should be about 2.2 times smaller (it is over sampled by factor of x2). Indeed - if we reduce it to 50% (a bit less than it should be - but easy to do in order to remove bayer matrix), and crop it to 100% "zoom level": It still looks good and sharp (above is just linear stretch - white/black point to show what is there).

Do include SW MN190 and ES MN-152 There are few high end models from Intes Micro - but no longer produced and maybe only available second hand.

I'd say RCs have the lead in that field.

What units are those? Pixels or arc seconds? Btw, your stars are rather elliptical with ~0.7 eccentricity. Do you have big difference in RA and DEC guiding performance? Usually if you have elongation in X axis (RA aligned to X and worse guiding performance in RA due to backlash and good balance) it is hard to spot in image.