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Hello everyone, After impulse buying this 80mm refractor a year ago, being very underwhelmed and returning it, I've stepped back and done a lot of researching of scopes & astronomy (mainly online due to Covid19). Now that I have a little better perspective on things I'm looking to get my first "real" scope and would welcome some advice. A lot of things I read and seen seem to suggest an 8" DOB being a good beginner scope one can grow into, without breaking the bank. Thus I'm leaning towards the Apertura AD8 with a Barlow & maybe additional lenses down the road, but again I welcome any advice or confirmation that this is a good first scope for me and my family? Other details worth mentioning: Price - A definite factor as I have no idea how hooked I or my family will become with the hobby. Last thing I want is an expensive dust collector sitting in the corner of the room. Definitely under $1k, preferably closer to half. If we end up loving it and I trade up, so be it... Interests - Planets and definitely faint & DSO's for sure (so I think that rules out low cost refactors?) Aperture - I know this is the most important aspect and people tend to suggest "Go bigger", 10", 12"+, and I understand the trade offs, but have no practical experience yet, so this is a difficult decision. Price, portability & light gathering are all considered here and why I feel the 8" is probably a good first scope size? (feel free to weigh in here) Location - I mainly see this being used in our backyard, which thankfully is pretty private & dark but we do live in the suburbs and there are stairs to consider. Maybe we'll take it camping or drive to a secluded rural spot once in a while, who knows... Size - Similar to aperture giving more light, I read that 10"and above start to become heavy & unwieldy. I'm no weakling but my wife and kids may want to use this too and the backyard is down stairs off our deck, so factoring this in.... Astrophotography - Probably not yet... My wife's a photo nut and has a couple nice DSLR's already. However, this seems like an expensive & time consuming rabbit hole, plus I would think you'd need auto-tracking mounts. Things could change down the road but for now it's not something I'm really factoring in. One can always google celestial pics right? Manual vs. motorized - I really don't know. I've read the pros & cons, people seem to be on one side or the other, and again astrophotography isn't a big factor at this time, so probably manual.... I was somewhat considering NexStar 6SE as it's barely under $1k, but thinking a 6" will limit DSO capabilities? The 8SE seems nice but we're talking $1200+ for bare bones. Also an interesting conversation I had with a rep from highpointscientific mentioned an 8" DOB would be more blurry and have less color than an equivalent 8" SCT, which got me worried about a DOB and seemed to contradicted things I've read, but again I have no practical experience here. All I know is I bought a $200 scope off Amazon a year ago that could view the moon and bird watch. Saturn and Jupiter were blurry, shaky, white dots, forget about DSO's. I returned that 4.5 star hunk of junk and wanted something more. I hear great things about DOB's far as viewing, but I'm not going to find an accurate video online of what one would really see through it for obvious reasons. So here I am looking for advice. Would an 8" DOB be a good first buy? Would it genuinely be able to see the planets well along with many faint and DSO's? I know a 10" or 12"+ would gather more light while sacrificing cost and bulk, but are they that big of difference between being able to see DSO's and not vs. an 8"? What I would hate is to buy an 8" DOB and immediately think "I should have bought a 10" or bought a 10" and never use it as it's too much of a hassle to lug down the stairs & setup? So C'mon experts, please bring it! If you made it this far, thank you very much & you'll have good karma for many moons to come!!!

I’m looking to find a dob like mount for a 12” BS Newt. BS 12" (length 110 cm) weight 18 kg. The only requirement is digital circles for push to support a Nexus DSC. Any ideas for a dob based mount? Has anyone used Astrogoods? https://www.astrogoods.com/mounts.singularity.collapsible.shtml

I threw an opinion into the mix in the beginners forum the other night and decided I should expand on my reasoning here. Even somewhere as benign as SGL, you still have to remember this IS the internet. That means opinions repeated enough by people with large post counts, gain credence as fact among the rest of the forum. It does not hurt to challenge that, if only to get people thinking, as long as you do it in a reasoned way. So..... What got me thinking was the humble 8" Dob. For instance, I've noticed that the most recommended scope for a beginner is an 8" Dob; 10" if there's a sniff of the OP having a bit more to spend. The thing is, a rake of this recommendation appears straight off the bat, without further quizzing of the OP, but for most newbies, I think it is wrong. True, a great many people started there and went on to bigger (some might say better) things, but a lot do not. You don't have to be Poirot to notice it's also the most sold scope on Ebay, along with the EPs it came with; reasons (excuses) of needing the space, etc, being given. The ratio of 8" Dobs for sale on Ebay is greater than on here. A lot of people don't stick with it long enough to achieve the fifty posts required for access to the classifieds. Why? Because if you don't know your way around the skies, you'll find it really hard to find stuff and you'll break your back grovelling around doing so. It is also a scope that will likely be way off the mark in collimation out of the box and be harsh on the rather basic EPs* it came with. When I started, my Explorer 200p only showed half the primary when looking down the focuser. They really can arrive that far out of whack and dealers these days are driven by price, so they are extremely unlikely to have seen more than the outside of the box you've been shipped. Few would actually check the scope and if they did, most people would whine they're too expensive. Service costs. So, if you do find something on your first light with your new scope and then pop in the 10mm MA it came with, it will look rubbish. De-collimate your scope with a half decent EP and have a crack at Jupiter. It's not impressive and that's as easy as it gets. For a n00b, it's confusion time. In other words, it's not the most intuitive scope, it has a built in steep learning curve just to get it to work and requires immediate upgrades just to get near what this, admittedly capable scope in the right hands, can deliver. The 8" Dob is best suited to someone who has at least used binos, or a friend's scope. That way, they'll have advice on hand. So my contention is that, in this push button, battery driven age, the ideal beginners scope is a 127mm AZ GOTO Mak. I can hear the hackles rising, so let me justify this. I'm not interested in the cries of 'It needs to be level, it needs to be pointed North!'. That involves a bubble level and the one star everybody knows. People who get the date format wrong should RTFM! Anyway, if this is tricky, how are they going to get along with a Planisphere? No, the learning curve is minimal and when the crisp little optics and it's long FL, which is easy on cheap EPs hits a target, it's going to be a sharp view. If it doesn't hit the target first time, the erstwhile n00b will slew around a bit and unless they're complete attention deficient, will hit the target. This is my point. Getting the first few targets a newcomer sees to be clear, is the hook that keeps them engaged. Jupiter will look good in a Mak. Saturn at any size when sharp is unforgettable. The moon will look amazing and M42, M57, globs, etc, will be good enough to show people there's a universe out there they hadn't even considered. I know an 8" Dob will do these subjects better, but it's not exactly Wow! territory. There are plenty of atmospheric UK nights and particularly from suburban locations, where a 5" Mak might actually do these subjects better. Now I know that hardly anybody reading this will still have their first scope, but if one of these had been, it would still be a great little grab 'n' go, plus a handy mount for an 80mm ED/Apo for the same purpose, plus white light solar, etc, etc. Nobody who starts in the hobby with an 8" Dob stays there. In the long run, rationally, the humble 5" Mak GOTO is a very handy little weapon on a number of levels and one that has uses further down the line. Russell * One of the scopes I bought at a time when my collimation learning curve had long since flattened off, came with the usual 10 & 25mm MAs. For a laugh, I thought I'd give them a go. You know what? In a 300mm F4.9 Dob, they weren't that bad. The deficiency I recalled, was in fact, mostly mine in terms of collimation - It was far easier to blame the EPs and post yet another 'What EP for a n00b' thread....

Hi All, My Skyliner 200p OTA will fit in my car, but the Skywatcher mount that came with it will not. Are there any foldaway Dob mounts out there? Or any diy projects? Ta, Neil.

In preparation for the upcoming "galaxy season", I have been busy re-organising my eyepieces across my eyepiece boxes. I am expecting to be using a mix of traditional and a-focal night vision observing. Therefore, I have put together a "mixed" case of eyepieces. There is a little space remaining just in case I need to swap in a couple more (but I don't tend to go outside will all my eyepieces in one go as they only get cold and unuseable, I prefer to leave a couple inside for a mid-session warm eyepiece swap-in! I have also created a new Sky Safari "brightest galaxies" observing list so I can target these larger/brighter galaxies with the night vision to hopefully tease out some views of unseen spiral arms? (most likely with the 55mm TeleVus Plossl) as focal speed is key to getting the arms. I may need to swap in the TeleVue Panoptic 27mm for more scale (but we will see)... [Here is the Sky Safari Observing List that I will be using Galaxy High Brightness.skylist should you wish to try it too…(you can import it into your Sky Safari - just email it to yourself then when you try to open the file in the email app it should offer you the chance to "open with Sky Safari") ] Having learned last year that night vision is not much help on the smaller galaxies (they just get overpowered by the super bright galaxy cores), I have the TeleVue Ethos 21, 13, 10 ready for some "traditional viewing" (with the option of swapping in the Ethos 8 as needed) on the smaller galaxies. I am eagerly awaiting the heavenly widefield views of endless galaxies as seen in Leo with the Ethos21 and the big dob! Last year turned out to be a "Supernova Marathon" with seemingly weekly supernovas occuring over the UK (and I managed to bag EIGHT of them with the Big Dob). NGC 3941 - SN2018pv UGC 5049 - SN2018pc NGC2746 - SN2018iq NGC3367 - SN2018kp NGC6217 - SN2018gj NGC3158 - SN2018aaz NGC2146 - SN2018zd NGC4151 - SN2018aoq I can't see that happening two years running but I did bag SN AT2018ivc (in M77) on December 1st. Tonight I will be targeting SN2019np in NGC3254 so here's hoping... Either way, I will need a good supply of clear sky, so lets hope our luck is in. Wishing you the best for Galaxy season, Alan

Does anyone happen to know the size of the small, black, flat-tipped, philips head screws that hold the primary mirror cell in place. These are the screws on the outside of the OTA at the end, just above the black "collar" of the mirror cell. Thanks.

I picked up my new (and first ever) dob from Nottingham yesterday. Its a 20" f3.6 Lukehurst dobsonian. It has a 1/10 wave mirror. David Lukehurst gave a quick demo of the scopes features and answered my questions on collimation. Then it was time to dismantle and put all the pieces into my car. I had taken some duvets and pilllows to allow me to get everything packed in and there wasn't much room to spare... Everything was unloaded into my garage just before dark. Today I have been making up some wiring to connect the various "enhancements" that will increase my use of the scope. David had fitted the powered ground board, 10K encoders and Nexus controller plus UTA dew controller unit (he cleverly wired the dew controlled up through one of the hollow trusses which is a neat solution) & secondary heater. He has added a few pass through holes in the corners that made it easier to get the cables out to the mirror box to connect up the fan & UTA dew system. Once that was complete, I got my neighbour to help me carry the mirror box from the garage down to my shed (obsy). Assembly was a breeze as David numbers each side and each of the trusses so you get them on the correct side (easy). I added the shroud then attempted collimation using the Howie Glatter laser & tublug. The secondary was almost spot on and the primary took a half turn before the triangle shaped centre spot appeared in the tublug display. I gave the Nexus a test with a false alignment on the sun and practised some push pull to find the imaginary mercury and mars. All seemed to be working fine. Just had time to fit my astro systems scope coat and see how much spare material there was as the coat is for an f5 longer scope. Anyway, too much cover seems to make the job of putting it on much easier Now, I just need a clear spell to get out and align the finder then we should be away! Alan

The coming wet weather is the perfect opportunity to treat my baby to some upgrades and mods. My XT10i is to be pampered with: Telrad finder on a 4" riser Primary mirror cooling fan Protostar flocking Bob's Knobs on secondary Moonlite CR2 focuser Fingers crossed it all goes well and my baby will be even more wonderful. :-)

Hi everyone, I was lucky enough to get a 12" Skywatcher Dobsonian (305mm/1500mm) for Christmas. It shipped with a 10mm Plossl and a 25mm Plossl, both 52° AFOV. Finally had a clear enough night to try it out and I absolutely loved it. I researched a bunch over the last year so I knew this was the scope I wanted should someone want to get me a really sweet gift before I grabbed it myself. What I didn't research at the time was accessories and equipment, something I've been doing relentlessly over the past few days. I'll primarily be viewing in the backyard until I find a great viewing spot (and a good way to safely transport). Light pollution isn't terrible but I haven't fully gauged its impact on seeing fainter objects. I'm not interested in imagery/photography at the moment. Not foreclosing on the idea by any means but everything I'm looking to add is purely for visual gratification at this point. Hoping the experts out there can lead me in the right direction. Here's what I'm trying to figure out: 1. What eyepieces should I pick up? I've read that, generally speaking, you want 2-3 premium pieces in over to cover low, medium, and high magnification. I'm currently looking at the following "sets": 5mm Nagler, 13mm Ethos, 35mm Panoptic or 6mm Ethos, 13mm Ethos, 21mm Ethos. I'm not overly concerned about price. I recognize that there's going to be a premium associated with a brand like TeleVue and with squeezing out that last drop of performance; however, I don't want to throw away money unnecessarily if I'm not going to see a benefit from pulling out the stops. I'm not beholden to TV by any stretch but everyone says they're the gold standard so I figured I'd look there first. I'm not looking to grab everything at once either. Was thinking of starting with the 13mm Ethos since it would fill the mid-range gap between my 10mm and 25mm. 2. Should I grab a Paracorr? I've read many comments that go back and forth on this but the consensus seems to be that, while it's not crucial at f/4.9 like it would be with a faster scope, it's something I should probably have in the arsenal if I'm using wide field eyepieces, which the ones I'm contemplating are. I couldn't detect any coma with the two eyepieces I currently have but I suspect I probably wouldn't given the FOV and my beginner status. I also think that once I see it I'm not going to be able to unsee it. 3. Should I pick up a Barlow? This question assumes I'm not getting a Paracorr. I like the idea of essentially doubling the number of eyepieces I have but I'm not too sure of the ultimate utility/necessity of it. 4. Any other crucial accessories I should have? I'm looking at a Cheshire collimator for when the time comes. Aside from that, is there anything else I should absolutely have? 5. Finally, any suggestions on transporting? It goes without saying but this baby is heavy. I don't have a garage, and I'm hesitant to store it in the shed, so what I've been doing is removing the OTA from the base and transporting them separately to the backyard for setup. It's not bad but I can see it getting old after awhile, especially with numerous viewing sessions in a row. After all, I didn't get this scope so it could collect dust; I want to use it as often as the weather lets me. I do plan on replacing the feet with wheels so I can at least roll it, but I'm trying to figure out a good solution to getting it in and out of the house (down 3 small steps) to the backyard without damaging it or breaking my back. I think that's all I have for now. I appreciate any help you all can provide. I'm just trying to learn as much as I can so I can have a great experience and eventually show my little guy all about the joys of astronomy. Thanks everyone!

Hey guys A guy in my area is selling a 13.1" Coulter Odyssey, the 2 mirrors. I'd want to get an idea on the optical quality of them. He bought the many many years ago, and they still in the original package, hasn't been used. 1. Would the optics degrade over time if they were wrapped up? 2. What is the general quality of the mirrors. I have heard the optics can vary alot, and they generally not that great for planetary views. 3. He is selling them (and he mentioned the Rocker once) for around $350, is this good for a un-used mirror. I'd like to build a really nice DSO / Planetary Dob, and this gives me hope if the optics are really good. Any advice, tips etc would be greatly appreciated. Tx guys

Hi, I have a skywatcher 200p dob and was hoping someone would be able to recommend an eyepiece with a wide field of view that would help finding objects and observing larger objects like the Pleiades. I have had a look at an explore scientific 30mm with 82° FOV, but was unsure if it would be good with my scope. Thanks Katie

Hello stargazers, I've been stalking this forum for a good couple months now in my search for a telescope. My main focus will be the visual observing of planets and DSOs. I like photography might plan that later if possible (i'd like it to be). The skies where i live is somewhat polluted but not so much. I can easily spot most constellations with the naked eye if my drive my car on a hill outside the city. I was thinking about one of the models below. I'd like the get the best bang for the buck and minimize the risk of being disappointed and then wanting a more expensive tube later on. I'd like to learn the sky by heart thus steering clear of a GOTO for now. I'm not going to buy anything right now because I'm putting some hard earned cash in a pair of binos first. My options: (but I'm open to any and all suggestions!) Skywatcher Skymax 150 PRO €569.37 + Skywatcher EQ5 Deluxe €269.02 Objective Lens Diameter: 150mm Telescope Focal Length: 1800mm (f/12) EQ5 because it's a good stable mount that I basically can keep using if I ever upgrade the OTA Skywatcher Skyliner 250PX Dobsonian €463.49 Diameter of Primary Mirror: 254mm Telescope Focal Length: 1200mm (f/4.7) Celestron Omni XLT 127 €647.16 Objective Lens Diameter: 127mm Telescope Focal Length: 1250 mm (f/10) Skywatcher Skymax 127 OTA €274.42 + Skywatcher EQ5 Deluxe €269.02 (Or EQ3-2 for €442.96) Diameter of Primary Mirror: 127mm Telescope Focal Length: 1500mm (f/11.81) I might also get the less stable EQ3-2 for a 100 euros less. But again, the EQ5 is a good investment I believe Skywatcher Explorer 200P EQ5 €504.55 Diameter of Primary Mirror: 200mm Telescope Focal Length: 1000mm (f/5) I got all the prices from FLO. Some questions that I still have: (thanks for staying with me so long) - Would you be able to see some DSOs with anything up from f/10? - Is a dew shield necessary if i live in the Netherlands? - I know its been asked a lot but what eyepieces would you recommend? FLO recommend BSTs. Then again which lengths? I thinks thats all for now:) Thanks so much for checking this post out. Clear skies to you all!

ok ,after some research and deliberation it seems the explore scientific range are highly regarded ,and read "near nagler performance" in some threads. so im pretty much sold on getting these. which focal length would be your first purchase (assuming you have no eyepieces ) also , has anyone any issues regarding viewing with wide angle eyepieces . I previously owned a maxvision 24mm 68* albeit briefly . I disliked the flat top design and prefer angled cup designs. Oh, and they would be initially used in a 250px f/4.7

I am thinking on grinding my own lightweight mirror (first f4 16", later f4 24"). The lightest and cheapest option is to get a thin blank and slump it in a decent kiln. Anyone has longer term experiene with slumped mirrors? Overall doesn't seem to be more work than a normal (not pregenerated) blank. Do I have to grind the backside as in case of normal flat back mirrors to avoid astigmatism? How do people support a convex back while grinding? Does it make sense to grind a hole in the middle for additional support? I am remotely considering a convertible Newtonian/Cassegrain system anyway...

Hi, I have a Sky-Watcher Skyliner 300P FlexTube GOTO which I am enjoying however after a period of no use the base has become very stiff. My fault, as it became wet not realising that the cover I had bought for it was not waterproof. Looking through the threads in here I found one which I followed to try to strip down the base however I have become stuck at the point of trying to remove the motor housing from the base after removing the 4 machine screws. I suspect that it is a combination of corrosion and the base material swelling which is preventing me from removing the motor from the base. When I release the worm gear from the static gear using the release lever the motor turns easily which is what is fuelling my suspicion. Any advice or suggestions would be useful as I've come to a halt in my investigation for the moment. It looks to me like I'm going to need a new base which may be a better bet anyway as the original supplied is heavy and definitely not good in the damp. Dom

Hi all, I want to share with you my so far best image of Saturn, taken using: 305/1500 goto dob Skywatcher QHY-5 mono IR-UV block filter Baader barlow 2.25 Registax, stack of 40 images, postprocessing

This is probably my options as of now:I will definetly buy a 12mm BST Starguider A 2X BST Barlow( So thats 100x and 200x magnification) AND Either: 15MM BST STARGUIDER VS 25MM STARGUIDER My dobsonian telescope will include:A 25mm and 10mm Eyepiece . So the obvious awnser is to go for the 15mm BUT i ve read in reviews that the bst s have are noticabely better than the eyepieces that come with my telescope.So i am wondering, should i buy the 25mm or the 15mm BST? Also is it worth to barlow either 25mm eyepiece to make 12.5mm and ditch the 12mm i am definetly buying for a 6mm one? i am thinking not because if i barlow the 6 mm it will give me 400x and i think that is too much magnification for the image to appear clear , plus i will also barlow the 10 mm to give me a 240x the acceptable limit for good clarity / magnification ratio (i ve read that and not sure if its true or not). Thanks again for your time and help! This forum has been very polite, welcoming and kind to noobs like me just getting into the hobby XD I hope i can one day look back at myself and laugh at my ignorance! This site has been truly amazing and i hope i can stay a member for a long time to come! Thanks as always Clear skies everyone Kronos

Found various threads on here and other forums about flocking dobsonians/newtonians but couldn't find specific images of disassembly of the very popular SkyWatcher Heritage 130p flextube and flocking of the OTA. So having ordered some DC-Fix black velour sticky back material (can be got from various places including FLO) I thought i'd share some photos of the process from start to finish as it may help someone else in the future... Images below with notes... 1. Focuser and shield flocking This was the easy bit. A strip stuck inside the focuser, and just unscrew the shield, draw round it, cut the material and align and smooth down. In the last image above you can already see the significant improvement on reducing reflections comparing the flocked shield to the unflocked tube... Notice my version of Bob's Knobs on the secondary mirror which are just black steel M4 25mm knurled thumbscrews bought off ebay for about £7 - along with the thumbscrews already on the 130P primary mirror this makes any fine collimation easy and completely tool free! For full stealth mode I've also painted the edge and rear of the secondary mirror, and any exposed screw heads with blackboard paint to reduce reflections. 2. OTA disassembly and tube before Note the cutout in the lower primary housing and the top ring. This aligns with the ridge of the tube seam, and means there is only one way to reassemble the telescope tube and mirror and one place for the handful of screws (4 at the bottom, 3 at the top). You'll also need an allen key to remove the 3 bolts for the dovetail mount. Simple! Now you're ready to Flock 'N' Roll! 3. Flocking the tube You'll need approx. 50cmx29cm of the material to do the tube in one go, starting along the seam. As others have described just take your time here, peel off about an inch of the backing and get the edge aligned with the tube seam stick down firmly and smooth out any air bubbles. Then slowly keep peeling more backing (rip and remove if the excess gets in the way) and smooth down as you go, turning the tube and affixing the velour material. 4. Finished flocking and close up during application so you can see contrast/reflection comparison of before and after. All in all only took around an hour so not a hard job as long as you prepare and concentrate! I ordered one sheet of 45cm x 1m material which was plenty, however if your not as confident you'll get it right first time then order 2m so you have more to spare if you need to start again. Looks great, so as always I now just need clear skies to go play and see the difference it makes!

Hi all not very good at gramma so stick with me ,Well I got the 16" reflector nearly a month ago and tonight was the first real night after the group meet the other night we spotted the primary with the , Catseye Hotspot & 4"-32" Centring Template (thanks FLO ) and set the secondary and job done . This dob sits at just over 6' 9" tall ,man handling it is a dream with the fear of god in me I took it all down the garden around 17:00 and checked colamination . I got out around 20:00 after a bit of family time and it being clear as a bell M42 This was a dream I first had a look with a 32mm plossl and it was just about all in very clear and the detail was unreal even a hint of greyish green and that's no joke theta 1s all 4 easily seen and sharp the nebula it's self was very nice the arms as I call them left and right were like a pair of wings ,the hook on the right of the neb was very prominent I switched to the 18mm celestron x cell lx the detail just got better and this ep gave me more detail and structure in the nebula NGC1980 This was great to view easily seen and just south of the main neb am sure I see a fuzzy patch of neb around this all star bright and sharp. M35 This again 25mm celestron e lux plossl and 25mm celestron x cel lx gave me a mind boggling view of this cluster I love it one of my faves I could see orange blue -ish ,white ,orange stars,very rich and deep diamonds do not describe this it was like seeing it for the first time again spent around ten mins looking at this , Orion's Belt Just panning around with the 25mm was great very rich in stars in the field of view M1 Very easy to find 25mm again a nice fuzzy shape very clearly a stretched oval shape and not much else to say M94 The Rigel finder made this usually faint fuzzy easy tonight no structure as it was low and around 21:30 by this time a small round fuzzy did not tale power well 25mm was the best view M82 Bodes This was the best I have ever seen and there was structure this time 18mm xcell lx the cigar shape had me screaming nearly the left side had a faint star in it ,I convinced my self it was the sn but new it could not be .faint detail in the centre and almost lines cutting through the whole of it M81 also,looked like a swirl a centre fuzzy with what looked like faint swirls just around it outstanding again I saw lots more stuff as well but do not want to drone on as you have seen them all before I had a few niggles,about dew ?,none at all ,not a bit at all .which was a relief as I have no idea how I would get rid of it. Home made shroud worked a treat made out of two camping matts and flocked at the bottom I brought two meters of spandex which a neighbours got busy with her sewing machine and made it a double piece with Velcro I may upgrade the whole scope with this .the campo,BG matts did not effect balance. The Rigel finder took a bit of getting used to and finding the right angle was hit and miss to start with but soon got the hang of it .its small and compact size is just right. Over all I am truly blessed to have purchased this scope and many of my fears of it's size and big mirror are gone I hope it stays clear every night as it's got so more to give . Has I said excuse my gramma and thanks for reading Pat

The Newtonian telescope design is both simple and remarkable. It is capable of producing a perfect image on axis, but off axis, the image quality degrades mainly due to an optical aberration called coma. Modern fast Newtonians and Donsonians of F/5 and below have a surprisingly small diffraction limited spot (just 2mm across in an F/4.5), where the image is not disturbed by coma. The Astro-Tech (also sold under the Altair Astro and GSO brand labels) coma corrector has been designed to cancel out this aberration to give a flat, wide field with high resolution from edge to edge. It is manufactured by Guan Sheng Optical (GSO) and was developed by Astro-Tech from a high quality, modern optical design by Roger Ceragioli My corrector came in a nice box and consists of two parts, the coma corrector itself and a 2" eyepiece adaptor which screw together with a 48mm (2" filter) thread. The eyepiece adaptor has two screws and a brass compression ring and is marked ALTAIR ASTRO 2", Coma Corrector, Made in Taiwan. At least I knew I had the right part, but no other documentation was supplied and I had to search the web for information on how to use it. Unfortunately the corrector is not ready for visual use as supplied, because of inadequate eyepiece spacing. The proper spacing is not critical and a compromise spacing to cover your eyepieces can made up with 2" extender tubes, such Hyperion fine tuning rings or empty 2" filters. You do not need a turntable like that of the Tele Vue Paracorr. With the spacers installed, the assembly which is now about 70mm long just slides into the focuser tube like a barlow. In this arrangement the focal point is moved in by a small distance of about 10mm (see photographs below). The corrector acts as a very slight barlow, enlarging the image by just about 10%. The lenses are nicely coated and reflect pale green. The aluminium housing is cleanly finished in satin black and the combined unit weighs about 350 grams. Once set up properly in a collimated telescope, the corrector works just as you would expect to give a clean, flat image. The view feels quite different, much more like a refractor, with pin point stars from edge to edge, but no chromatic aberration. Objects can be allowed to drift across the view of wide angle eyepieces with little or no visible loss of sharpness. The removal of coma can be clearly demonstrated by doing a star test on and off axis without the corrector installed and then with it. Any loss of contrast due to the extra corrector glass (two doublet lenses) in the light path is undetectable, I think. The coma corrector is now a permanent fixture in my focuser except on occasion when viewing planets with my 200mm Newtonian which now has a motor drive. It seems to me that a coma corrector should be a standard accessory for all fast Newtonian telescopes and particularly for larger Dobsonians with no tracking. This model is an effective, affordable example and I strongly recommend it. The first issue is actually finding one in stock. Supply has been patchy over the years and at the time of writing, it is listed by Astronomics (Astro-Tech brand at $135, including T-mount, but out of stock), Agena (GSO brand at $130, including T-mount, but out of stock), Ian King (Altair Astro brand at £88) and Telescope Service (GSO brand without visual adaptor at 61 Euro). There is then the issue of setting it up properly and most of the remainder of this review is devoted to showing how this can be done, but first there is a little information about Newtonian telescopes and coma. Newtonian telescopes are all designed with a single figured mirror in the shape of a parabola rotated on its axis, a paraboloid. All mirrors of a given focal length are the same shape. If you have a fast mirror, it is easy to to create a slow one of the same focal length, just by blanking off the outer part of the mirror. It is the outer part of the mirror that generates coma, which is zero on axis but which increases linearly the further from the axis you get. At the focal surface, the amount of coma is independent of the mirror focal length so a single corrector will work for any Newtonian. In practice, a perfect corrector is not attainable so the designer will aim to produce the best result he can for a specific F/ ratio, F/4.5 for this model I understand. However, the corrector will give good results for mirrors that are somewhat faster than this and for all slower mirrors. Coma correctors would actually be better called Newtonian correctors, because the designer is looking to produce the smallest attainable spot size for a point source, so will also be looking to reduce the other lesser Newtonian aberrations, field curvature and astigmatism. To do this, he will have in mind a particular focal length, around the longest that is commonly used (so about 2000mm or slightly less), because these aberrations are less in longer telescopes and it is wise not to over correct significantly. Newtonian telescopes are perfect on axis, but coma damages image quality at even a modest distance off axis. At the focal plane, about 1mm off axis, in an uncorrected F/4.5 Newtonian, the image is just at the diffraction limit and the strehl of even a perfect mirror has fallen to 0.8. In a 250mm scope, this gives a coma free, sharp field of about 6 arc minutes across, about 1/5 of the apparent diameter of the moon. For comparison, the field stop of a 9mm orthoscopic eyepiece is about 6mm so only the central 1/3 (1/9 of the area) of the view is free of coma in an F/4.5 scope. Coma increases sharply with the speed of the telescope, at the focal surface inversely with the cube of the F ratio. Collimation is the business of lining up the coma free sweet spot with the centre of the eyepiece axis. The tolerance for collimation is perhaps 1/4 (though some would say 1/6) the size of the sweet spot so that it covers the centre of the eyepiece. So far as I can tell, this tolerance also looks good for a telescope fitted with a coma corrector. To set up the GSO coma corrector properly, the total back focus (distance from the last lens to the focal plane) has to be about 75mm. The designer says that it is not critical and from 65mm to 85mm will produce a good spot size. This distance will be made up somthing like mine below, added to the height of the eyepiece focal point height above the eyepiece shoulder (or subtracting the height below the shoulder). 1.25" My 2" 2mm 2mm Spacing from last coma corrector lens to the shoulder 45mm 45mm 2" adaptor spacing 11mm .... 2" to 1.25" adaptor (if any) 19mm 19mm Spacers (Hyperion 14mm ring + empty 2" filter) 77mm 66mm Total (excluding eyepiece distance) My one 2" eyepiece has a focal point above the shoulder, and my 1.25" eyepieces are all within -12mm/+8mm of nominal, so are all fine. Tele Vue is unique in publishing the height below the shoulder of the focal point for all their eyepieces. For other users, you are going to have assume the focal point is close to the shoulder or measure the position. First, locate the prime focus by taping a piece of tracing paper to the top of the focuser and focusing on something. This does not have to be at night and can anything sufficiently distant so that it comes into focus, such as a church spire or distant tree. It does not depend on the telescope so using a refractor with a graduated focus scale is very convenient. You then measure how far in (plus) or out (minus) you have to move the focuser for each of your eyepieces in turn. For users only intending to use 2" eyepieces, a single 28mm Hyperion tuning ring might be fine. If you do not like the idea of finding empty filter rings, or more likely buying cheap ones on eBay and removing the glass, some suppliers (in particular Telescope Service) have spacing rings with the right 48mm thread, in a few sizes such as 10mm and 20mm, but these are generally expensive. Variable spacers are also available but these are not going to sink into your focuser tube. When I first set this up I had to remove a 2" to 2" adapter to allow the unit to go all the way into the focus tube. This left too little out focus so I made a plastic washer (from a yoghurt tub, see photo below) to prevent the corrector slipping all the way into the focuser and providing the necesssary out focus. One correspondent who uses only 2" eyepieces has done away with the eyepiece adaptor and has simply added enough extender rings to screw the corrector to each eyepiece as he uses it. I hope that this will is enough information to set up this corrector properly but I would welcome questions, and of course comments and correction.

Hi All,i hope you are safe n well,right then,i need advice on the issue of my rigel quikfinder base not adhering sufficiently( my opinion) to the sticky strips that came with it. I was wondering if that clear double sided gorilla tape would suffice? i would very much welcome your thoughts on this,thanks everyone Mark

Hello guys,my 8" dob is arriving soon. I have trouble setting my expectations Since i have looked through my 3 " dob its hard picturing what i could see with an 8" one.i live in a light polluted city. Can i look at any dsos directly? How will they look like using adverted vision? What can i expect to see? Also which all around filter should i buy (2") to look at dsos and maybe some planets? Thanks Kronos

Good Morning, Does any of the guiding softwares out there auto-correct a sync scan auto dob, with the use of a guide scope? The main use would be to to keep Planets in view so several runs of imaging them can be done in a session. I notice my XT8G does drift out of view ever 10mins at 250x. If I wanted to take gifs or many shots of something I'd need it to stay more dead on for longer than that. I have gotten as close to perfect gps coordinates, time to the second etc. Thanks Enrico

We decided to build a shed to house our Dob, which was taking up way too much house space. As to design, @ollypenrice suggested that we build a large 'skateboard' upon which we should sit our shed. The board is made from a sheet of plywood onto which the wheels are mounted. The wheels we chose were the ones used for sliding gates (we have something similar on our roll-off-roof shed. Here is the shed on the rails. The rails themselves were mounted onto concrete, steel reinforced lintels which were concreted into the ground: A slot is cut into the skateboard to allow it to fit around the base of the Dob: It seemed sensible to put down some sort of circular patio, and we discovered that you can buy kits. It was a little awkward cutting the slabs around the tracks, but I am happy with the final result: Before After And finally, the completed project with Dob in situ. We used a green strap - the thing you use to keep your suitcase closed - to stop the Dob from rising up in the shed (without an eyepiece it is a bit rear heavy): We chose materials for the shed that would match those of our existing ROR observatory (from Home Observatory UK - https://stargazerslounge.com/topic/245177-home-observatory-uk/):