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It's not bad example - it is realistic example. We can never have exact conditions what we want, so there will be variability even if your guiding is spot on and always the same. What you really want to know is whether you'll be able to make good use of the kit and under which circumstances? Well, to answer that - maybe it would be best to put it in perspective and compare it to some other piece of kit? Or at least set certain goal? Maybe you want to image fast and don't really care about resolution? In that case, just determine resolution that you want to image at, and just make sure you are not over sampling in majority of conditions. In most cases with such aperture, you won't be oversampling with 2"/px, so you'll need to bin quite a bit, but you'll get very fast system (254*254*2*2 = 258064 - just compare that with any of the "Speed" numbers above to get the idea). However, in order to do that - and still get sensible field size for 2"/px - you'll need very large sensor. Maybe you want to image with at least HD pixel count (1920x1080px) as final image, and with modern cameras that have say 3.76 pixel size you need to bin at least x5 - that means you need almost 10000 x 5000px camera - or ASI6200 (and field flattener to be able to properly illuminate full frame). Maybe you don't want that, maybe you want some balance - and want to image galaxies at 1.5"/px. Then you need bin x4 (or perhaps bin x3 if you use some sort of reducer) and you can get away with APS-C sized sensor or maybe even 4/3 if you want to image smaller galaxies. In this case, however, if you expect your mount to perform only to 0.8" RMS, you better only image on nights that are 1.5" FWHM seeing (or very good seeing nights). If you get your guiding down to 0.5" RMS - then you'll be ok even at 2" FWHM seeing for that resolution. Even if you don't achieve these - you'll get image, don't get me wrong and you'll get it "fast" (compared to other setups) - but it will be a bit more soft than what is possible at given resolution (now, when I say a bit more soft - that is what I really mean. Most people produce much softer images because they over sample by fair a bit more than this - and this softness is only visible at 100% zoom - it might not be visible when image is looked at full screen if image pixel count is bigger than monitor pixel count). If you however want to be serious about high resolution work and want to attempt to really capture image at say 1.15" FWHM (this is just number when you bin x3 above pixel size without reducer but it is close to what can be achieved in very good conditions), you'll need to guide very good and have very good seeing (and it will take longer as you are now using "slower" setup than either of cases above because you'll be working with 254*254*1.15*1.15 = ~85000). You'll need to guide at 0.4" RMS in 1.5" FWHM seeing. If your seeing is say 2" FWHM you won't be able to achieve that resolution with essentially perfect mount (one that has 0 RMS). When I say you won't be able to achieve - I simply mean in mathematical terms of close to ideal sampling - it is probably best read as "your image won't be as sharp as it is possible given 1.15"/px sampling rate, but a bit softer when viewed at 100%". Hope this explains things a bit better?

I'm not sure that I understand what you are asking? Guiding is independent of resolution at which you are imaging. You can guide the mount and not have scope and camera on it at all. What you want to do is get your guiding and mount performance in general to the best level you can comfortably achieve. Guide RMS is contributing factor in overall FWHM that you'll be able to achieve. Other two being seeing and aperture size (for diffraction limited scope or spot RMS in general). Those things combined will determine how sharp your image is and whether you are over sampling or not given your target sampling rate. It is the only factor that you have some influence over after you've chosen our scope. You can't influence seeing. Once you have decided on your scope, only way to change its aperture size is to replace it (same thing goes for mount of course). Only thing that you can somewhat tweak is guiding parameters and mount in general (like some mods to make it more stable, more precise). We often say things like "You need to guide at half of our sampling rate", but these are very rough guidelines. What we should really be saying - make your mount performance the best you can (and that is really inline with other recommendation - and that is that mount is the most important part of imaging kit) as it will in part be determining factor whether you should bin x3 or x4 later (if your primary goal is high resolution).

This seems to be the answer: https://www.firstlightoptics.com/adapters/astro-essentials-m54-adapter-for-sky-watcher-newtonians-and-72ed-refractor-m54.html but probably best check with FLO before ordering if it will truly work for our use case.

Not silly question at all. Some glass wearers can observe without glasses and some can't. It really depends on what sort of eye problem we are talking about. If it is simple near/far-sightedness then you don't need glasses when observing. Telescope focus compensates for this and one can get perfect image (but people not wearing the glasses will need to refocus the telescope to get sharp image). Cylinder / astigmatism type of eye problem can't be solved with refocusing alone and one needs to wear eyeglasses. If wearing the eyeglasses will be problem when observing depends on eye relief of the eyepiece. There are eyepieces that are designed to have long eye relief (meaning position of the eye can be further away from eyepiece itself to fit the glasses in between) and can be used with eyeglasses. Out of two eyepieces that come with scope - I believe that 25mm one has enough eye relief. Shorter 10mm one - won't have for sure. For shorter FL, different eyepiece can be purchased. These are very good and have good eye relief and won't break the bank: https://www.firstlightoptics.com/bst-starguider-eyepieces.html With above scope, I would not go below 8mm. 5mm will give too much magnification, and won't be usable. 8mm or 12mm can be purchased to replace stock 10mm as they are close enough in focal length and have enough eye relief (16mm).

Just to add - there are a few reviews of that telescope on youtube which are worth checking out:

Hi and welcome to SGL. Based on what you've said, I'd recommend this scope to you: https://www.firstlightoptics.com/sky-watcher-starquest/sky-watcher-starquest-102mc-f127-maksutov-cassegrain-telescope.html It is light weight and can easily be moved It has a tripod that is sufficient given the size of telescope Telescope can operate in alt azimuth mode (simpler for beginner), or equatorial mount - better for planetary observation but needs a bit getting used to, which can come with time. It is in price range, but can be upgraded with tracking motor for better experience when looking at planets at higher power. With suitable diagonal prism (amici / erecting prism) - it can be used during daytime as a spotter scope as it will provide upright and properly oriented image (for astronomy it does not matter how image is oriented, but this scope normally reverses left and right when used for astronomy - so needs special addition for daytime use. Most telescopes have this or similar reversal, but with this it is easy to correct with relatively cheap part if one wants spotter). In general - this telescope's strong side are planets / moon / stars. I would not recommend however that you use it from within a room (nor any telescope for that matter). Image seriously degrades when looking thru the window glass, and temperature difference causes issues. Telescopes work the best when the are outside and cooled to ambient temperature - so garden it is.

Ok. That is good - but I would check few things. First is attachment. As far as I can tell - you can unscrew 2" nose piece on that flattener to reveal M54 thread according to Flo: From what I quickly gathered around the net - 72ED also has that thread on focuser (once you remove clamping ring). Maybe it's not the same thread and you'll need adapter - but it might be the same, in which case you can just directly screw it in. Screw in connection is much much better than clamping one as clamping one can easily introduce tilt. I would also experiment with 55mm back focus - back focus depends on field curvature of the scope which in turn depends on focal length of the scope. 55mm should be seen as a guide line - not as a precise thing, unless reducer/flattener is optically matched to the scope. Here are stars in corners of your first uploaded image: defined core + ring is sign of either very poor chromatic correction (like when you don't use UV/IR cut filter) or sign of defocus. other corner shows similar thing - but astigmatism as well. Third one is not as bad: still a bit defocus but not as bad as other two - which suggests there is tilt On the other hand center of the field shows nicer stars compared to corners: All of that is indicative of tilt and field curvature (different focus position for center and edges of the frame) - which flattener is supposed to correct. If it's not correcting, but is present - it usually means spacing issue. For tilt - check if you can switch to threaded connection For curvature - try playing around with spacing to see if you can get better results.

I'm guessing that there are several issues with this image. 1. Poor transparency / high altitude clouds or perhaps even foggy conditions at the imaging site - there is certain "softness" to the image that indicates this 2. Lack of field flattener and some tilt issues. What can be seen as poor focus is actually due to field curvature and tilt in my opinion 3. Lack of flat fields

I haven't really payed much attention to that new SA GTI. For some reason, I'm not really a fan of whole SA series, but this one seems to be much better in terms of what it can do than previous versions?

Still use it, although I've upgraded counterweights and I've got myself 3d printer since (must have for any serious DIY astro amateur), so it now features several 3d printed bits Those are x3 0.5Kg weights from Decathlon. I believe they were like 1 euro each or there about. https://www.decathlon.co.uk/p/cast-iron-weight-training-disc-weight-28mm/_/R-p-7278?mc=1042303&c=BLACK 3d printing helps with bore diameter and makes for nice hand adapters for nuts for easy height adjustment. In any case - that is probably most cost effective upgrade on my equipment so far

I think they are roughly in the same category as far as imaging performance goes. I would not image on either with anything but the smallest scopes or just camera and lens (up to say 200mm). AZ-Gti has advantage that is dual type mount - you can use it for quick grab n go observing sessions, with even long focal length scopes like maksutov for planets. It is also very compact and portable. SA/SA2 is star tracker that is very portable. You can put it on photo tripod. EQ3 is much more heavy / bulky, but it performs roughly the same as far imaging goes. For visual it will probably hold a bit larger scopes. I would put 6" F/6 newtonian on EQ3 for visual - but no way I would put it on AZ Gti. AZ-Gti runs on AA batteries, but you'll need power supply for EQ3 or run it of 12V battery. AZ-Gti probably guides a bit better - but I can't be 100% sure on that. This is based solely on their construction. I own AZ-Gti and have opened it to adjust it and clean it. It has spring loaded worm gears which help with backlash. I haven't yet guided mine (although it sits ready for guided imaging - just waiting for me to come to my senses), so I can't really tell how good it will be, but I think that both mounts guide around 1.5-2" RMS? SA/SA2 can only be guided in RA direction (which means that it can also be dithered only in RA direction). Hope this helps

So it is two stage after all! Even so, very thin driving pins can't be avoided - these look like 2mm ones.

Friction drives are prone to slipping if they are not balanced well enough. I agree with you, but as far as I know - all friction drives out there are in fact single stage. I also think that there is no rubber involved either. It is precision machined steel against steel with enough tension. Worm is intentionally avoided with these designs because of backlash. Pure friction drive has no backlash and it guides exceptionally well because of this - it is very responsive. This is primarily design intended for imaging and as such even suffers from "random" periodic error (misnomer, I know - can't be periodic if it is random) - but tracking error is small enough and smooth so it is easily guided out. This design is intended to be guided for imaging. If I were to design friction drive, I'd probably go with two stage design. CNC machined cycloidal drive for motor reduction and then 50:1 - 100:1 friction drive.

That is alt-az mount that can be turned into equatorial mount for long exposure imaging. It is this mount: https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/sky-watcher-az-gti-wifi-alt-az-mount-tripod.html It has a lot of features - like wifi connection, ability to be controlled via computer and tracking in both axis. EQ mode is rather simple conversion. You need to load special firmware (that lets you select if you want mount to be in EQ or AZ mode - so you don't loose alt-az capability), addition of wedge to be able to polar align and addition of counterweight shaft and counterweight. You can either get dedicated wedge and CW bar - or you can DIY one for start like I did here: (wedge is simple ball head and CW shaft is M10 thread with some washers acting as counterweights).

Hi. Friction drive consists of large disk and very small diameter "pin". Top view looks like this: It is a bit like spur gears - but without teeth: Ratio of diameters of large and small roller is reduction. You need to have enough reduction to be able to achieve sidereal rate. I've done calculations for stepper motors and if one wants better resolution than one step per arc second (and usually for high end mounts you want at least 10 times higher) - you need around 200:1 reduction (if stepper is 200 steps per revolution or 1.8 degrees and one uses micro stepping of 32 or more). I don't know much about servos, but I believe they also have resolution? Right? They have internal encoder that is making sure servo is at correct position? Either look up for that to be enough compared to tracking precision - or see what is lowest RPM that motor can achieve and see to make it some fraction of sidereal (like 0.1 of sidereal). In any case, for higher end mount, I believe that you need at least 300:1 reduction. That would mean 300mm disk and 1mm pin. Pin needs to be pressed against large disk somehow. Maybe spring loaded or something like that. I believe there is open source version of friction drive, let me see if I can find that for you, maybe you'll get some ideas there. It looks like I was wrong and that OGEM is not in fact open source: https://www.cloudynights.com/topic/612391-open-source-gem-from-jtw/ However, take a look at E.fric as well for ideas, although I'm not sure if you'll be able to see the friction drive itself in the images. http://www.geminitelescope.com/efric-friction-drive-mount-german-equatorial/

You don't have to have similar focal length. Similar focal length is important if you want to keep the pixel size the same - but you don't have to do that. Imagine you have F/5 scope of say 4" and F/10 scope of 4". 99% of people will say that F/5 scope is faster than F/10 scope - but that is not true. In fact there is no true statement. F/5 can be faster than F/10 F/5 can be equally fast than as F/10 F/5 can be slower than F/10 F/ratio is not indicator of speed. It is only useful for comparison if we keep pixel size fixed across setups (use the same camera). If we use the same camera as is on F/5 and F/10 - F/5 will be faster If we use the same camera on F/5 and F/10 - but on F/10 we bin pixels x2 - they will be the same speed (twice larger pixel cancels out twice longer focal length - as sky surface is the same and aperture surface is the same because both are 4" scopes). If we use camera with larger pixels on F/10 and bin x2 and we use camera with smaller pixels on F/5 natively - F/10 will be faster.

Well, how about 8" RC on Heq5? You see, if one wants to image galaxies - one does not need much in terms of FOV. Most galaxies will be nicely framed by FOV that is half a degree or so. There are only hand full of galaxies that are larger than that. Now, we have half a degree - say in width. That is 30 arc minutes or 30 x 60 = 1800 arc seconds. If we assume that we are going to obey physical limits of what the telescope can resolve in long exposure - then there is no point in going above 1.5"/px. That is only 1200px in width. Most newer DSO cameras will waste FOV on such a fast scope. On the other hand, If we bin camera to get larger pixels - then it really makes sense to get camera with say 3600px or 4800 px in width. Then we need scope with enough focal length to bring those binned pixel to wanted resolution. Fast scopes come with their fair bit of headache inducing problems. For one - they are not diffraction limited, which means that their spot diagram will further limit sharpness of the image / achievable resolution. Speed is not always in F/number, and once you account for everything - newtonians might not be the cheapest scopes . Both 6" RC and 6" CC are less than £500 - and don't need corrector over 4/3 sensor. They are light and compact and will ride well on HEQ5

No Ok, on one side - you might be right, and it could be faster as is - but we would need to calculate that. Speed is defined as "aperture at resolution" - or to be more precise, aperture surface times pixel surface (in arc seconds) So LZOS would natively be 130^2 * 0.63^2 = ~6707 Units and 10" RC would be 254^2 * 0.38^2 = 9316 Units 10" RC would be about x1.5 faster natively (if everything else is equal - QE of sensor, transmission of optics and so on). However, part of original post is quoting what can be achieved in terms of resolution - and I advise for both scopes not to aim over their maximum. I would bin 130 at least x2 to get 1.26"/px and I would bin 10" RC at least x3 to get 1.14"/px When we do that, applying again above formula we get: 130^2 * 1.26^2 = ~26830 254^2 * 1.14^2 = ~83845 That is 83845 / 26830 = ~3.125 times faster. (if you wonder why we multiply squares above - from each point in the sky - all photons that fall on aperture are focused in single point - aperture surface is proportional to square of diameter, and all those photons in all points that fall on one pixel are added up to form pixel signal - there is "surface in the sky" that is covered by pixel number of such points - which is again proportional to pixel side squared). That is why I said that 10" scope can be roughly x4 faster. In fact, if you exactly match sampling rate between the two (by binning or using appropriate sized pixels) - 10" scope will be exactly x4 faster than 5" scope (10 * sampling rate / 5 * sampling rate)^2 = (10/5)^2 = 2^2 = 4. Make sense?

I would try other software for DSO imaging instead of SharpCap. SharpCap is my go to software for planetary and some quick work (and would be my go to for EAA if I wanted to do that now), but I prefer to use ASCOM drivers for long exposure imaging, and I'm used to other software with that. Give Nina a try? In any case, I'd use gain of 120 - I like working with unity gain. As far as exposure goes - as much as you can do without visible trailing. I don't know how precise is SA2, but there is a limit to exposure length that you ought to use. It depends on light pollution and you need to swamp the read noise with background signal. I believe that sharp cap has capability to calculate this value? https://www.sharpcap.co.uk/sharpcap/features/smart-histogram If you don't know how to calculate it yourself - I think above calculator will give you at least rough idea. Go with that exposure length if your tracking can make it work (no star trailing).

When you slew the mount with hand controller - you can select slew speed in multiple of sidereal. I think that SW mount supports from x1 up to x800 for slewing (even less than x1 for guiding). If your hand controller is set to this lowest speed - x1, then it will take quite a while for you to notice the move. With this sampling rate it will only move few pixels every second, so it would take holding that button dozen or so seconds to be able to notice the difference in position on the screen.

For me there is, if you can afford it and "field"/operate it, but question is - what do you hope to achieve? Sure, someone with excellent seeing and maybe not so good equipment (like 8" scope) will be able to match your image as far as resolution goes, but resolution is only part of the story. There is also speed part. Larger scopes have potential to be faster (if matched with appropriate camera and handled accordingly). Here is an example. You take 10" RC and pair it with say ASI6200, while someone else takes APO from LZOS 130 (so 5.1") and pairs it with ASI533 or ASI183 That will give you same FOV, so images will be comparable - but you will image yours with 10" of aperture for photon collecting while someone else will do that with only 5" - so 1/4 of aperture by surface - or you will be about x4 faster if you also match resolution / sampling rate (which I would advise you to do). Even if person with 5" APO uses larger sensor - they will need to crop on most galaxies to get nicely framed result. Most of the galaxies are small enough for smaller FOV offered by longer FL. While larger telescope and better mount can provide you with higher resolution - even if your seeing prevents that from happening - there is always speed factor to take into account.

If you can reach focus - you don't need additional extension tubes. In order to figure out if you can reach the focus - find bright star that you can easily see in short exposure. Iterate exposures and look at the disk formed by defocused star - moving focuser will make defocus disk either larger or smaller - go in direction when it's getting smaller. At some point it should reach "pinpoint" size and then it will start expanding again. If you can make that happen - you have enough back focus, but if you reach the end of focuser travel as it the disk is getting smaller - but you can't reach that turning point - you need more back focus distance. Is there a way to mount small finder scope next your scope? Even simple red dot finder will do the trick. First align it to main ota using an eyepiece and bright star. Then you'll be able to put target somewhere on the sensor. After that - you need to do frame & focus exposures. Short exposures where you'll be able to recognize target (in stretched image, capture software usually has auto stretch function for this purpose) - and then you manually move your mount to center it.

That is normal, there are several things that will make your goto be less than perfect. You really need to do test exposures to see if target is nicely framed (so called frame&focus exposures), or you need to do plate solving to have automated centering (that is advanced thing and requires use of computer to recognize star patterns and direct mount to correct location).

UHC is not very suitable filter for broad band targets like M31. It is much more suited for Ha regions and emission type nebulae. For above target - it will do more harm than good. IR/UV cut is necessary if you want to remove star bloating and get good color. In general - it might not be necessary with UHC type filter - but that depends on UHC filter itself. This is transmission curve for Optolong - UHC and we can't really tell (but it looks like it might need UV/IR with it as well) - because it seems to have transmission above 700nm (part of graph is missing, so we can't be 100% sure - but it does look like it is not falling back to zero). You can stack filters - and resulting curve is multiplication of two curves - if either one is zero - result will also be zero (no transmission, as 0 * any number = 0).