vlaiv

If price difference is significant for you - go with cheaper - 290 might be a bit better - but certainly not twice better - not even 10% better in my view.

If diagonal is preventing you from seeing airy disk and rings - change diagonal ASAP!

Never really compared the seeing mask on / off. People say that smaller aperture fares better in poor seeing, and there is some merit to that in theory, but I don't have any hands on experience in that field.

I would not bother with barlow lens. x300 is way too much magnification for a scope like that. If it was perfect optics scope - I would not recommend going beyond x240 in magnification. As it is fast achromatic refractor - it won't do well over say x100-120 - maybe x150 with fringe killer. Alternative would be to stop it down to 80 or 90 mm and again go with say x150 max. Instead of barlow lens - maybe look into getting one really wide field eyepiece like this one: https://www.teleskop-express.de/shop/product_info.php/info/p2334_TS-Optics-35-mm-2--UFL-Eyepiece---69--Field-of-View---6-Element-Design.html As far as eyepieces go, maybe best option would be to get BST starguiders: https://www.firstlightoptics.com/bst-starguider-eyepieces.html These are very decent quality affordable 60° AFOV eyepieces that have enough Eye relief and work ok with fast scopes like F/5 Aperture mask works wonders on fast achromats. I tried it both for imaging and visually. With ST102 if you just take cap of the middle of the scope cover - it leaves hole that is 2" in diameter and you get 2" F/10 achromat. If you observe Jupiter say at x70 or so (500mm FL and 7mm EP) and then switch to this view - you instantly get sharp image free of chromatic aberration.

My first impression was that your collimation is not very good. If you look at your image, stars somewhere right and below globular are the most round ones. Opposite corner to that shows most coma / elongation. I would first collimate the scope without CC to get round stars in center of the FOV and equal amount of coma in the corners (so that image is symmetric) and after I would work on CC spacing to get best correction.

First thing to try out would be to rotate the camera by 180° and see what happens. If there is tilt in camera / camera adapter - it can be revealed that way as aberrations will rotate with camera. If they stay the same - then it is collimation issue. 8" version has primary mirror fixed to back tube and those are aligned at factory and should not get out of collimation. Larger models have decoupled primary and back port and have tilt adjuster at the back. I doubt that back port is out of collimation with primary - as they are "one unit" and move together - therefore you should try primary collimation using single star positioned in different corners and looking at defocus - you want level of defocus in each corner to be the same / minimal - compared to center of the field.

Yes, that is poor collimation. Although central part is not problematic - edges are and that is due to primary mirror tilt. When collimating RC - you go thru set of adjustments - you adjust primary to fix peripheral issues and then align secondary to get round defocused pattern in the center and then you repeat until no further alignment is necessary. I have found this guide to be particularly useful: https://deepspaceplace.com/gso8rccollimate.php

ST120 is interesting scope, and although ST102 has 2" focuser as well - ST120 simply has more aperture and can quickly be turned into sharper scope - by using aperture mask. You can make mask that goes over the front of objective lens that has smaller aperture than the scope itself. Say you want to lower chromatic aberration and get sharper higher magnification view. Your scope is 120mm F/5 and thus 600mm of focal length. You can easily make 90mm aperture mask that will turn your scope into 90mm / 600mm - F/6.66 scope that is better suited for high power viewing and lowers chromatic aberration. I used to do that with my ST102 by using simple PVC water sewer pipe plug like this: Here ready to be drilled. You can say choose to make 100mm mask and at F/6 that will give you better planetary performance than ST102 that is F/5. It is good choice - but do be aware of the size of that scope, and also - if you can, get it on AZ4 rather than AZ3. I had both of these mounts - and AZ3 is really very basic mount and not very good. I don't recommend it. Your new account at Astronomski Forum is also approved and you should be able to login to it now (although it is experiencing some technical difficulties - beyond my control, admins should be dealing with it).

In Registax there is option to align RGB channels. It may help to improve image somewhat.

Does scatter change as you move your eye around? If so then you might need to clean your eyepieces. I often have such issues with my eyepieces because of long eye lashes - it is very easy to grease up eye lens of the eyepiece and that creates distinct light scatter. Another thing that creates scatter is dust / smoke / humidity in the air. These present more like halo around objects (both planets and stars) - that does not move / change as you move scope and you eye around. If there are forest fires near by or you have large body of water like a lake, swamp or river and temperature is high - you could be having issues from the atmosphere.

I don't know for sure. What I do know is that I've seen images taken with that scope and GPU CC and ASI1600 and I had no objection to correction of the field. I usually have objection to stars on images taken with fast newtonian scopes. Rarely are stars tight and without distortion over the whole field. When I look at spot diagrams - they rarely represent anything close to diffraction limited optics. Have a look at this comparison of performances of coma correctors: https://www.astrofotoblog.eu/?p=856 Do note that camera used has Kaf8300 sensor - which is 22.5mm diagonal sensor - so 4/3 format and look at corner stars. Telescope used is F/4 10" newtonian.

I think it is a good scope - but not sure if it will be that good with APS-C and Full frame sensors. I would personally use it as wide field instrument for imaging with 4/3 sensor and suitable coma corrector (GPU CC for example). One thing that I really like about F/4 version is that it has longer tube than other F/4 newtonians - which is good. What I don't like is gap around primary mirror. It is good for cool down but care needs to be taken when imaging and taking darks - as there is great potential for light leak.

Makes one want to get 16-20" dob just to image the Jupiter

As far as I know, hole on Mak102 is smaller than that on Mak127. It is about 22mm if I'm not mistaken. According to one image online for Mak127 it is about 26-27mm 32mm Plossl works in my Mak102 but I have a few objections to that combination. First is vignetting in daylight - I can quite notice it. Second is eye relief. It is by far the most eye relief that I had in EP/Scope combination and sometimes this bothers me. 32mm Plossl is otherwise very comfortable eyepiece for me, but with this scope - it is not so.

AS!3 lets you create multiple stack in single go (different percentage of frames stacked) If you put in some value in respective box - that stack will be created and if you leave 0 - it will not be created. You can thus create 10 and 20 percent stacks by specifying either 10, 20, 0, 0 or 20, 10, 0, 0 (not sure if other combinations work as well - I ever used only ones where unused slots were to the right. I did however use all 4 at the same time - and it works - it creates multiple stacks).

zDotUp is scalar value, but look what it is: It is product of length of both vectors and cosine of angle between them. a is celestial up and b is z. z has unit length so ||b|| is equal to one. a*b = ||a|| cos(theta) scaling is multiplication / division of length of vector with some scalar value. If you divide vector with its length - you get unit vector in that direction. What does scaleVector function do with its parameters?

Larger darker blurrier image that is the same as one at lower magnification. People seem to think that somehow magnification plays a part in telescope image - but it does not - or at least not in that way (it only impacts image after it has been formed by telescope - like if EP is not sharp enough). Telescope forms image of certain resolution at its focal plane - regardless what sort of eyepiece is in the focuser - or if there is even any EP in focuser. Eyepiece really acts as magnifying glass. You can tale EP alone and whatever you place at its focal plane (field stop of EP) - it will be seen clearly and magnified - you can try this at your computer screen - unscrew 1.25" barrel of simple EP and place it against computer screen showing some image - you'll be able to see individual pixels! What happens when you magnify too much - well nothing really except that image gets darker as light is spread over large area. This happens: If you see this with normal magnification: then you'll see this with x3 that magnification (roughly, I'm just simulating light loss - not doing proper calculation): Some low contrast feature will simply vanish because image is darker and there is less contrast, but they are still "there" and if you use camera instead of eye - you can enhance contrast and still see them.

Maybe this diagram will help: Given some vector that represents direction of zenith from where you standing - you want vector in direction of where is north - again along the surface of the earth. That vector is 90° away from Celestial Up - but in direction of Zenith. Green arrow is projection of Z along Celestial up and you need to reverse that and add to Z to get Celestial north vector. float zDotu = scalarProduct(upCelestial, z); part calculates full dot product which is cos(angle) * len(celestial_up) * len(z) If you scale celestial up with that value - len(celestial_up) cancels and you get only cos(angle) * len(z) - which is projection of Z along celestial up. Minus sign in trueNorthCelestial = addVectors(z, scaleVector(upCelestial, -zDotu)) serves to point green vector the other way so it can be added with Z. It won't be normalized from above calculations. Z is unit length - and from above diagram - you can see that celestial north is shorter than Z - so it is not unit length. If unit length vector along celestial north is needed in rest of the code - it is just simply normalized. Have no idea what you are asking here, but if you have two coordinate systems - like celestial one related to person holding the phone and phone coordinate system - related to phone orientation, then transformation from one to other is rotation, and rotation is multiplication by rotation matrix. So in order to transform from one to another - you need to calculate rotation matrix and multiply with it. Axes of phone are just regular X,Y and Z and they are not given by rotation Matrix. Rotation matrix serves to transform given vector from one space to other space by rotating it (same way that phone is rotated - or rather inverse of that). Here is simple diagram again: Right coordinate system is rotated by 45° - but right person sees arrow as pointing straight UP - so it has (0,1) coordinates in that coordinate system. But in left coordinate system it is no longer pointing up - it is pointing at 45° and has coordinates (0.71, 0.71) (or which ever is right number there). It is same vector on image, but if we want do draw it we need to draw it at an angle, but if rotated person wants to draw it - they need to draw it straight up - they have (0,1) coordinates, we have (0.71,0.71) coordinates - in order to switch between these two, one must use multiplication matrix that goes something like sqrt(2)/2 0 0 sqrt(2)/2 (as sin(45) and cos(45) are square root of 2 /2 or 1/sqrt(2)).

Indeed. Whole OTA seems like most reasonable way to go. I'm sure people will be interested in purchasing only collapsible OTA for travel and mounting on photo tripods and light weight Alt Az mounts as well - so it can be relatively easily exchanged.

Seems that clever people already thought of doing that and it works fine

I wonder how feasible would be to replace it with something like this: https://www.teleskop-express.de/shop/product_info.php/info/p7836_TS-Optics-1-25--Crayford-Newtonian-Focuser---metal---with-T2-connection.html That one has base plate that is removable: and what is left is probably the same size as focuser of Heritage 150? As far as I can see from images - it looks like stock one is cast together with upper assembly? That might be a problem for modding to most.

Indeed, I think it is best to go by 500 or 550nm - which would be teal or mid green as short wavelengths are the most affected by seeing and arguably will be most distorted. Difference in between 400nm and 500nm is only 20% and if you under sample blue by 20% - it will not matter really. Excellent spreadsheet.

What do you intend to do, planetary imaging or long exposure imaging? In either case - Dawes limit has nothing to do with pixel size. In both cases, it is bad to go with smaller pixels than are needed - question is, how do you determine size of pixels that are needed? In planetary case, it is simple - there is maximum resolving power of the telescope and minimum pixel size is dependent on that. found here: https://en.wikipedia.org/wiki/Spatial_cutoff_frequency You need to sample with two pixels per minimum wavelength corresponding to max / cutoff frequency. With planetary imaging this is done by changing F/ratio of your system - for given pixel size you can determine critical F/ratio and then use barlow lens to produce that F/ratio. With long exposure imaging - it is star FWHM that determines optimum sampling rate and that is not something you know in advance. You can only take average FWHM that you are likely to get for your conditions and base pixel size decision on that. Star FWHM will depend on aperture size and optical properties of your telescope (off axis aberrations and correction of those), your mount / guiding performance and of course, the most important factor - seeing. Once you establish likely FWHM that you will be getting with your system - then sampling rate should be FWHM / 1.6.

Yes, maintenance can be issue with systems that have mirrors. Newtonian scopes require collimation and in principle, Maksutov telescopes also do. I own couple of reflector telescopes - 8" newtonian telescope on dobsonian mount and 8" RC type reflector. I also have Mak102mm. 8" dob holds collimation very well. Much better than I first thought it will. I drove with it couple of times to Fruska Gora and it keeps collimation. I probably need to touch up on it once or twice a year. RC is photographic instrument and it also holds collimation well. In fact - I did collimation only once when I got it and will have to do it now again - but because I messed with collimation screws and not because it came out of collimation itself. These are larger and heavier mirrors than Maksutov telescope. More weight there is in mirror - more likely it will go out of collimation. I don't think you really need to worry about collimation that much. You might need to tweak it once when you get your scope - and maybe not even then - mine came in perfect collimation. Other than that - maybe once in few years. New Maksutov 102 telescopes from SkyWatcher even come without collimation screws. This is probably due to weight saving, but also because most people never needed to touch up collimation on their small scope (I still decided to get version with collimation screws just in case). Other than that - you'll need dew shield for night time. This can be DIY thing - piece of PVC pipe of right diameter with some felt lining or similar. I think that these small Maks are virtually maintenance free most of the time. As far as robustness - well, it is delicate piece of kit. It has front corrector lens and back mirror, but it is very light weight (at least 102mm model is). You should handle it with a bit more care than your monocular - but nothing special. When transporting or storing it - use some sort of padded bag for example and make sure you don't put anything heavy on it. I think that you will get instant feel for what can and should be done - once you take it in your hands. You'll see that scope optical tube walls are not quite thick and with right kind of pressure it will bend. It feels like it can be easily scratched by keys or screwdriver or similar. Other than that - thing feels quite solid in hand and nothing will fall out or fall apart even if you shake it All in all - I don't think that you need to worry much about these things - it certainly should not put you off from having that scope if you feel is right for the type of observing you are interested in. As far as getting the gear in Serbia - I have experience with three different retailers. Our local retailer deals exclusively with SkyWatcher gear and is often cheapest option due to import and shipping fees. I ordered from Teleskop Service in Germany and from FLO (sponsor here on SGL). FLO has very competitive prices but main problem is very steep shipping charges for larger items. On smaller items it is quite affordable (for eyepieces or similar it will cost something like £8-10 for shipping, but for items the size of telescope it can be couple hundred of pounds). Teleskop Service has somewhat steeper prices now and also raised their shipping fees - but can sometimes be the best option (large items get shipped for ~30euro - which is quite ok). P.S. If you signed up for our local forum (Astronomski Forum) - but did not get confirmation e-mail there, that is because you mistyped your e-mail address - as yahoo.con instead of yahoo.com . Your account has been approved and you should be able to access it now (I'm moderator there fighting spam bots and approving new members manually ).

Size of telescope / aperture is important for several reasons: 1. Amount of light it gathers. This part is not really that important for terrestrial viewing, but it is very important for celestial observations. It helps see fainter stars and fainter objects. Given your requirements of both type of viewing and budget - you are really limited to 4" to 5" scope depending on type (4" refractor or 5" Maksutov). That is plenty of aperture to see all sorts of things from dark location. City lights really ruin the night sky as far as faint objects go - nebulae, clusters and galaxies. 2. Resolved detail at high magnification. Larger telescopes have potential to resolve more detail - but that potential is often limited by atmosphere for night time viewing of the sky. In any case, maximum useful magnification will depend on your eyesight (people with sharp eyesight don't need as much magnification as people that don't see that good). General magnification is in range of x1 (excellent sharpness of vision) to x2 (medium sharpness of vision) per millimeter of aperture. With 100-125mm telescopes (4" - 5") that turns out to be between x100 and up to x250 with larger scope. For planetary / lunar observation atmosphere often limits magnification to max x200. You can figure out how much magnification you'll get at say x100 on terrestrial target in following way: Eyepieces that come with telescope are often 50° of apparent field of view (a bit larger field of view than that monocular). With x100 magnification that turns into 50° / 100 = 0.5°. That is about 5mm held at arms length. Take for example Aspirin pill and hold it at arms length - everything that is covered with that Aspirin will be "in front of you" when looking thru a telescope at x100 magnification. Lowest magnification will depend on type of telescope that you get / focal length. If you are used to x8 provided by monocular - this will be new experience as even lowest magnification will be at least x2 that if not more. Back to telescope choice - you really have two choices - refractor and maksutov type telescope. I'd recommend getting AltAz type of mount for your telescope as EQ mount is very unsuited for your use (daytime and balcony, especially if you can't see Polaris to do polar alignment). Maksutov will have very high magnification range as it has long focal length. There are really two choices 4" model or Mak102 - 102mm or aperture (from different vendors - like Skywatcher, Orion or Bresser for example) or Mak127 - 127mm of aperture (again from different vendors and most have both models as they are scaled versions). They have focal lengths of 1300mm and 1500mm respectively. Magnification is calculated by dividing telescope focal length with eyepiece focal length. Eyepieces start at about 32mm and can go down to just few mm - like 3mm. This means that Maksutov scopes will have lowest magnification at x40-x45. That is rather high magnification compared to your x8 monocular. These scopes are very good if you want to have high magnification capability. Good for planets, the Moon and double stars. Their weak side is that they are somewhat slower to cool down - larger the model - it takes more for it to cool down properly so that view is steady (at those magnifications every little thing is magnified and so are thermal currents in the air and scope itself). They also can't provide low magnifications / wide field of view. Refractor telescopes come in two different types (this is very arbitrary division aimed at explaining your options - not general rule). Long refractors and short refractors. With refractors, you'll be limited to 4" or 100mm (or smaller models) due to price. They will be achromatic refractors (no exotic expensive glass so chromatic aberration will be present). 90 / 900 and 100/1000 refractor models are considered long refractors. They are slightly shorter focal length than Maksutov telescopes - but still quite long. Minimum magnification is about x30 on this scopes (so four times what you are used to). Long refractors tend to be sharper scopes with less chromatic aberrations. They require little to no maintenance (this is true for both short and long refractors) and their cool down is very quick - you can be observing in matter of minutes (in winter time it does take 10-15 minutes for scope to properly cool for high power views). Their drawback is that they are physically long telescopes - like 1m in length so space for use and storing is consideration. They look like "proper" telescopes - something people like as they can be kept in living space as decoration when not in use. Short refractors are telescopes for wide views and lower magnifications. They have focal length of about 500-600mm. This means that you can have as low magnification as ~ x20 (even x15 which is only twice what you are used to). They don't cope well with high magnifications, so it is best to keep them up to say x80 or possibly x100 and not above as they tend to show much chromatic aberration (purple fringing around bright objects and high contrast edges). They are light, don't shake as much as longer tubes when in use. The telescope that I recommended above 90/660 is somewhere between the two refractors. It is short enough to enable you up to 2.5° of true field of view with right eyepiece and x20 magnification, yet is long enough to comfortably enable magnifications up to say x120-140. It is light / manageable for use and storage.