Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_celestial_motion.thumb.jpg.a9e9349c45f96ed7928eb32f1baf76ed.jpg

Search the Community

Showing results for tags 'dobsonian'.



More search options

  • Search By Tags

    Type tags separated by commas.
  • Search By Author

Content Type


Forums

  • Welcome
    • Welcome
  • Beginners
    • Getting Started General Help and Advice
    • Getting Started Equipment Help and Advice
    • Getting Started With Observing
    • Getting Started With Imaging
  • Community
    • Official SGL Announcements and Events
    • SGL Challenges and Competitions
    • SGL Star Parties
    • Star Parties & Astro Events
    • Celestial Events Heads Up
    • The Astro Lounge
  • Retailers
    • Sponsor Announcements and Offers
    • FLO Clearance Offers
    • Supplier Reviews
  • Astro Classifieds
    • For Sale / Swap
    • Wanted
  • Equipment
  • Observing
  • EEVA (Electronically Enhanced Visual Astronomy)
  • Imaging
  • Science
  • WADAS's WADAS Discussion Forum
  • Beaufort Club's Topics
  • Swindon Stargazers Club's Topics
  • East Midlands Stargazers''s Topics
  • Central Scotland Astro's Topics
  • SGL Cumbrian Skies's Topics
  • Herts, Beds and Bucks Group's Topics
  • SGL East Anglian Group's Topics
  • South Leicester Observers's Topics
  • South Wales Group's Topics
  • SGL Surrey Observers's Topics
  • South Yorkshire Stargazers's Topics
  • Yorkshire Astronomers's Topics
  • Devon and Cornwall's Topics
  • West Midlands's Topics
  • Essex Cloud Dodgers's Topics
  • Essex Cloud Dodgers's New equipment
  • NLO and Planetarium's Topics
  • Astronomical Society of Edinburgh's Discussion
  • Dorset Stargazers's Topics
  • Hairy Stars Club (Comets)'s Tutorials and Guides
  • Hairy Stars Club (Comets)'s General Discussion
  • Hairy Stars Club (Comets)'s Observing Campaigns
  • Hairy Stars Club (Comets)'s Analysis results
  • Hairy Stars Club (Comets)'s Useful Links
  • Pixinsight Users Club's Pixinsight Discussion Forum

Calendars

  • Astro TV
  • Celestial Events
  • SGL Calendar
  • Astro Society Events
  • Star Parties
  • WADAS's Events
  • Beaufort Club's Events
  • Astronomical Society of Edinburgh's Events
  • Dorset Stargazers's Events

Blogs

There are no results to display.

There are no results to display.


Find results in...

Find results that contain...


Date Created

  • Start

    End


Last Updated

  • Start

    End


Filter by number of...

Joined

  • Start

    End


Group


AIM


MSN


Website URL


ICQ


Yahoo


Jabber


Skype


Interests


Location

Found 95 results

  1. Hi all, Last night was the best night of astronomy I've had in my short time delving into this passion. It was simply incredible. Fortunately my dear friends the midgies have departed Scotland for another season. This means I can now stand at the scope without ingesting a lungful of tiny biting insects and concentrate on what I am observing. Always a plus! Two nights ago I went to my local dark spot with my 200p SW reflector. It was wonderful. LP map shows Bortle 4, but I would actually say it was a 3 or possibly a 'bright 2' when the lights go down a bit in the wee hours. Last night, I took the 20" dob and parked up. I am finding it easier and easier to move this beast around, but it's still a little bit of work to set up at the end of the day (literally). It can't all be so easy! I'm fairly new to astronomy and my scopes haven't seen a huge amount of use. After several failed attempts to get the GOTO working, I finally sussed it last night. It was just a few simple things really - small errors on my part such as a misplaced washer which blocked the azimuth from using its full range of motion, combined with a limited view at home which prevented me from doing a successful align. A huge relief to get the GOTO up and running, but I now feel a bit like I'm cheating! I don't feel guilty enough to not use the GOTO however Frankly, it's brilliant and was putting objects bang in the centre of the EP. I arrived about 6pm yesterday so plenty of time to set up. I left my counterweights at home and thus ended up strapping a small vinyl bag of tools and tyre jack to the underside of the mirror box with a tie-down. Worked really well actually! Can fine tune by removing a spanner or two. A few drops of rain blew through just before dusk but then rapidly cleared off, so all systems go. I tripped over the power cord after my first successful align. And then did it again a minute later after my second align! Will need to tidy that arrangement up or put some of my glow tape on the cable. Plenty of practice then doing an alignment, haha. M57 Ring Nebula for starters, I've been playing with my Baader 36mm aspheric quite a lot lately, I like the wide views. The Ring was fairly small through the 36mm but bright and crisply defined with an apparent faint blue tint. I then swapped to the 21mm Ethos and OIII which stayed in the focuser most of the night. Next stop was NGC6960, Western Veil Nebula or 'Witch's Broom Nebula' which was mind-blowing. It appeared as a silvery apparition which threaded right across the sky and extended well past the FOV from the 21mm Ethos. Scanning along its wispy tentacles was amazing. There's something unnerving about viewing it, it gives me goose-pimples, just otherworldly. The Eastern Veil and Pickering's Triangle in the central area were also clearly prominent, albeit slightly less luminous than 6960. The Veil was also clearly visible without the OIII, but with much more 'background noise', i.e. stars competing for attention. Following this, I slewed over to the Cocoon Nebula, but only saw a very dark lane practically void of stars. That was interesting in itself as it was so apparent by virtue of its darkness.. I don't know if I bumped the scope alignment of if I was just too impatient to punch another object in to the handset, but didn't spend a huge amount of time chasing it. In hindsight, I think I slewed to the wrong end of the dark lane. I'll find it next go. I then lined up on the Crescent Nebula which was easily visible, lots of fine filamentary details observable after some time studying it. A beauty. Next was Dumbbell Nebula which practically looked 3D through the big dob, just jumped right out at me. Another simply amazing sight. I spent quite a long time staring at it and could easily see the entire shape and structure extending from the 'Apple Core'. I remarked last night it looked like it was hanging inches in front of the scope. That's sheer aperture working I suppose! At the end, I spent some time just slewing around and having a mesmerising look across the sky, just taking in the depth and variable magnitude of stars that a big scope can display. I was already running on three hours' sleep from the previous night and by this time, I was starting to crash but was on a natural high. I crashed into the bed happily. Can't wait for another clear night with the big dob. I was a bit worried a few weeks ago that I'd bought something I didn't have the time or skill to fully appreciate, but getting the GOTO up and running and being able to rapidly slew to various objects really put things into perspective. My 200p is a wonderful, portable scope, but in comparison, 20" of aperture is simply a completely different level. It is like the difference between a small grainy 640px video and high definition 4k with the brightness cranked right up. Tonight I shall stay in, sleep well and dream about how much discarded glass is needed to cast a 36" mirror blank and how many years it would take me to figure it... Clear skies all
  2. Very happy with it! Wish the sky were clear, but as we all know, when we buy astro equipment, it's cloudy! Argh! The telescope was collected from David Lukehurst at noon and then we travelled back to Cambridge. John Nichol primary mirror: 37mm thickness, Suprax. Hilux coated. Optics 1/8 PV wavefront 1/27 wave RMS. Strehl .95. Secondary mirror: 62mm MA. Here a few photos:
  3. Hello folks, for long I have been browsing the internet to find a suitable 10in dob and despite lack of reviews, I have decided to take the plunge with the Bresser Messier 10in Dobsonian. There was some doubt at first, especially when considering the popularity of similar scopes from Skywatcher, Meade and GSO. Even though Bresser is relatively new to the market, it has some clever features: 1. The massive 2.5in hexagonal rack and pinion focuser is very solid and the movement is smooth. Despite being only single speed, Bresser sells an a dual speed 10:1 extension. However, I find the movement precise enough and do not need the extension at the moment. 2. Optical finder scope feels a bit cheap but it is a nice upgrade over the red dot finder I had on my previous scope. 3. Rocker box style base allows disassembling the scope into two pieces (OTA and base). 4. Tube rings allows the scope to be easily balanced when adding weight + after adding a suitable dovetail plate, the OTA can be used on an equatorial mount (if you plan to upgrade to an eq mount, I would consider the 8in model, as an eq mount for the 10in would be expensive). The only negative comments I can give about the scope is the production process. There were some minor issues with the assembly with the scope as parts did not fit properly. First problem was with one hole drilled deeper (loosening the particular screw fixed the issue). Another problem was with the altitude wheel as it made the OTA to pop out from the rocker box. (A loose screw on one of the plastic pads between the box and altitude wheels was causing this. Make sure all these screws are tightened and below the surface of the pads). Lastly, I assume there must have been a mistake in the quantity of items included (I got twice as many screws for the rockerbox and 2 eyepieces instead of one, both were 25mm super plossl but the standard was a 1.25in advertised on the bresser webpage, while the other was a 2in wide angle) I did not have the opportunity to test the scope outside properly due to clouds. Update: 01.06.2017 Had the chance to try it out on the moon and jupiter to a max magnification of around 160x. The results were very sharp and detailed views. Unfortunately, clouds rolled in before it got dark enough to observe DSO's. I am waiting for clouds to clear and a package with a 42mm wide angle eyepiece and a 2in GSO 2x ED barlow to arrive next week.
  4. Hey guys. After many years of waiting, I've decided to finally go for my first telescope. Yet, today find myself stuck between two excellent entry-level options, so I'm looking for some help. Before I get straight to my questions, I'd like to share some information about what I'm expecting to do with the equipment (among other stuff). - Objectives: Deep Sky, and some planetary observation. No interest in astrophotography, GoTo, or any other device (maybe/eventually in the future). - Budget: Given complementary I'll be getting a 2x Barlow (SkyWatcher; achromatic), and a starguider laser collimator (1.25-2), these are my two best available options to fit on its range. - Light pollution: Low-Med. Being that said, here are my questions: - Mount: After days of heavy research, so far hardly found a review about it; What do you guys think about the AZEQ AVANT type of mount?; Could it beat Dobsonians?; Would it be a better option in my case? and if so, why? - Conventional Tube vs Heritage's Compact Flex Tube: What are the differences (pros-cons) I can expect from one and the other? (despite no difference between mirrors and diameter). - Explorer 130P AZEQ AVANT (newbie question): Would it be possible to transport the whole structure armed from one spot to the other in my yard? Any help/opinion welcomed. Happy 2019!
  5. A couple images I was able to take with my iPhone and my Dobsonian XT8. using the Camera +2 app Anyone know any other good phone apps? ?
  6. Every time I need something - eyepiece, star map, etc. - it's either just out of reach or swinging the dob around knocks over the gear table. I've just cannibalised a folding chair to make a table that moves with the mount. It clips to the turntable with some pipe saddles. John
  7. The boxes arrived a while back and packed in alongside was the cloud curse of the new scope. Build quality was good and the base was easy to assemble if you used the video instructions on the Orion website. The instructions in the box are not so good. I was torn between the 10" and the 12" but opted for the 10" mainly for handling reasons. This is a big heavy bit of kit and it is easy to handle if you take the tube off and move it in two bits. Assembled I can just manage to pick it up and waddle the 10 meters from the garage to the deck. In the upright position I just bend my knees and place my hands at the top of the holes in the side panel and lift. In the book they show a different method which I think risks your scope and back.... I like the shape of the base... much nicer than a bland boxy thing. Collimation was achieved using the supplied collimation cap. Three big locking screws and big adjustment screws made this quite an easy task. Having been used to an 8"SCT collimation was not one of my core skills so I acquired a Baader Lazer collimator , followed the instructions to the letter, adjusted the scope to "LASER" standard and being a cynic checked it with the collimation cap. It Looked horrid so did it all again with the cap and sent the Baader back. The star test on polaris last night was GREAT.... First Light..... The conditions were......100% very thin high cloud with some thicker bits mixed in. A little light pollution from the village street lights . Vega , almost overhead was visible and so was Ursa Major . Others played hide and seek to the naked eye. Now to upset some of you.... The 9x50 right angled finderscope is very good and gives nice views. Later I found myself just cruising round using this to explore. It is not however easy to instinctively align to the area you want to look at. I have a knee problem and am not going to get down on the deck to sight up the tube for a rough guide. I have fitted an Orion double scope bracket and the second slot now boasts a laser finder from Rother Valley Optics. A few tweaks to match the laser to the cross hairs on the finder scope and away we go. Point the beam at Mizar (laser on for about a second), Check Mizar is centered on the cross hairs of the finder and focus with my Panaview 26mm and focus........ Mizar splits as it appears dead center in the ep. Its so easy and so accurate and its my solution to the limits of a 90 degree finder and a bad knee but please guys dont take it to a star party it upsets some of the neighbors and take care where you point it. I live under an airway and inside an airfield Air Traffic Zone so I look and listen before use. Moving this beast around Alt and Az is very easy and very controlled...I LIKE IT Next on to Polaris to do my star test which was good. Just about to enjoy some stargazing and the cloud thickened....well its the curse of any new scope. So off to bed with the alarm set for silly o clock to wait for Orion to rise. More in hope than expectation I rose to find Orion just visible through the cloud. With naked eye I could just see M42 as a lighter patch in the high thin cloud. Lets have a look then ... WOW I am impressed. The light grasp of this pulls in a fair view of M42 with the Trapesium clearly visible. So what did first light with this scope teach me. 1. I LOVE DOBS 2. Its worth getting the scope out even with high cloud..its surprising what you can still see . 3. Laser Collimation is not for me. This scope is nice to use and gives great views ( I haven't commented on the standard ep's that come packaged, you need something better). I haven't tried the push-to setup yet but will comment when seeing is conducive to hunting DSO's.
  8. Hi, I've been eyeing an Explore Scientific 12" dobsonian for a while (primarily due to easier collimation). But a few days ago I noticed there was a 20% sale at my local retailer on Explore Scientific's 16" dobsonian and I am thinking I should just go ahead and get one. The big question is, is this too big of a telescope for a first timer (don't really have any experience with observing DSOs and planets)? Only experience I have prior to this is a 70mm skylux from Bresser (My dad bought it for me 15 years ago) which I've used to watch the moon primarily. Any advice or thoughts are appreciated Edit: Been lurking on this forum for a while, soaking up information. This forum is great for newcomers!
  9. Hey guys, i need your help once more. I was planning on getting the orion xx12g so i could do some visual observation but planetary imaging as well. If I were to connect a webcam such as the neximage, does anyone know if I can focus the camera or if I would need to get a barlow? I live in Woodstock Ny so light pollution is not very strong (on charts I think its a dark green zone). Would i need to get a 4x or 2x powermate/barlow? If anyone can help me that would be great. thanks
  10. Hello all, hopefully this is in the right place, i recently bought a 10" Skywatcher 250px Flextube, now i've had it a while i am looking to get some better quality eyepieces and now have my heart set on the Celestron X-Cel LX series as they seem good for the money and i really like the look of them, so anyway my question is what would be the best choice if i could buy 2 of them from the whole set for my scope, i am getting the Celestron X-Cel x2 Barlow aswell at the same time. Link with the sizes below. https://www.firstlightoptics.com/celestron-eyepieces/celestron-x-cel-lx-eyepiece.html i will get them all in time but for now 2 and the barlow would be fine. any help would be great, as i have read about the lenth of scope being a factor etc, but i do not truley understand it yet Thanks Limey21.
  11. I recently came across this website on constructing equatorial platforms for my 10" dobsonian telescope. http://www.reinervogel.net/index_e.html?/Plattform/Plattform_e.html I realise that there is a UK company that has restarted limited production but I wondered if anyone has experience of: (a) using a similar platform. (b) making one. I am intrigued by the concept and challenge of self build and would appreciate any tips. John
  12. westmarch

    Hello everyone

    Hi all, after years with an ETX 90, I finally got myself a dob. Bought a Meade Lightbridge 250 on eBay - good price and well looked after. Fitted a Celestron RACI finderscope and, as the scope nosedived, realised that the friction brake wasn't going to cut it. Fitted a lump hammer to the mirror fan fixings and that seems to have balanced things out, although altitude still has a bit of "stiction" - any advice appreciated. Unfortunately a neighbour has fitted a security light to the apex of their house and the sensor points at their central heating vent. If ships ever get past Tadcaster then there is certainly no danger of hitting rocks in Wetherby. I took it out for a dark sky airing to Yorkshire Moors. It took about 15 minutes to assemble and collimate - rediscovered the pleasures of star hopping after years of faffing about with Autostar. Good views of the Orion nebulae and Andromeda galaxies and located Uranus - a first for me! (You have to be careful how you describe that event to friends and family.) Dew cancelled play after about ninety minutes, so cue for more mods. I have put together a shroud with old tarpaulin and a black foam camping mat, cobbled shrouds for the finders and am still working out how to make a foam collar stay on the end of the OTA. (An air duct quick release clamp is currently under investigation but it may be too heavy!) Look forward to any advice and tips as I continue my bumpy progress.
  13. Hey guys I've been interested in getting myself a fairly large dobsonian, but which is portable enough to carry alone ,I have an ancient 6-inch on an alt-azimuth mount(Quite the relic,belonged to my grandfather, but that's a story for another day, haha I've had my eye on the skyliner 250px for a while now,so I wanted to ask those of you who own a skyliner 250px,either normal or flextube versions, about the weight and size of the scopes in question,and about the weight(as written on the boxes they came in) and the size of those boxes. You see, I'm from Pakistan, and I'll be visiting the UK for a short time in a few weeks, and figured I would indulge myself and get a new telescope. Issue at hand is getting it back in the plane though, and if I could get some weights/measurements beforehand, you would make an astronomer very happy, haha. Oh, and suggestions are very welcome too, if you have any better ideas about what scope I should go for. I do apologize wholeheartedly if this is in the wrong section though, it seemed the most appropriate at the time, but I've not used this site a while, so i'm probably wrong, haha
  14. I found a used Deep Space Explorer 8" for sale online. It comes with a collimator and several lenses, as well as a telrad finder scope. The price is lower than any Dobsonion I've seen before, $75. I am just getting started in the stargazing hobby, especially with telescopes, so I was wondering the opinion of you kind folks. Would this be worth buying? Why or why not? Thank you!
  15. Hie folks, Wanted a mount for astrophotographt, but buying one for my 8" dob is really expensive. Nearly 3000$. I recently came across a dob dual axis eq platform. What would be your suggestions on this. ???It is a motorised dual axis dob platform with hand controls and costs about 550$. Yes il b using an autoguider to keep the object i want centered. Any suggestions...?? Please feel free to share youe thoughts.
  16. Attempt number 2 at processing Jupiter. Finding it incredibly frustrating trying to image with my current set up, so have invested in 'Making Every Photon Count' to help me decide what I should upgrade to! Composite image of Jupiter and 3 of its Galilean moons Canon 70d, 8" Dobsonian (prime focus and manually tracked) 1 x 30 sec video, stacked, for Jupiter I attempted eyepiece projection, but couldn't achieve focus... no doubt I am doing something wrong, but couldn't work out what!
  17. It is a solid tube scope made in the UK by Darkstar, probably in the mid to late 1990s. It comes with a Telrad finder and I can throw in a finderscope if you prefer. Focusser is a Skywatcher dual speed crayford. The build is that of a traditional dobsonian with a plywood rocker section which provides a solid foundation and smooth movement. The mirrors could do with re-coating, but are still quite usable. This scope could be well described as a light bucket; the optics are not great (maybe a half wave?) and are really only suitable for low power views. However, it is pretty good for deep sky viewing. From my pretty good location I have seen tricky objects such as three of Stephan's Quintet, the Flame nebula, M51's arms, NGC 5053, C17 and much more. The previous keeper to me used it for galaxy hunting and amassed an impressive catalogue of observations. The scope is just too big for me to use frequently and I tend to get out the ten inch instead. However, I hope it could make a good instrument for someone else. Obviously this is too big to post, so it is pick up from mid Wales (Llanwrtyd Wells) or Penarth. £250 or offers/trades.
  18. Hi, I have bought a new meade 8" dob (as in the pic ) and i have the skywatcher 130P goto scope. I was wondering what you pro's think of either of these 2 scopes and also give me an idea of how much better my results will be when using the bigger scope? my guess is that the bigger scope lets in more light and therefore I will get a clearer brighter image with more colour? note that I have to wait for delivery of the dob and i am very exited about it, also at christmas I am going to get some 20x80 bins (celestron sky master) and im looking forward to that to (this is because i found andromeda galaxy in a cheap pair if 10x50 bins and i was a bit disappointed with the result, I dont have a decent pair of bins yet). so, what do you thing of the 8" dob? thanks in advance.
  19. 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.
  20. Hello, I am sorry in advance if this specific subject has been discussed before, but couldn't find it. In any case, I need your wisdom I am a proud owner of the best-seller Skywatcher 200P Dobsonian (8" 203mm aperture, 1200mm FL). Like many, I started relatively cheap because I wanted to know if I'd love the hobby or not. Turns out I did. Also like many, after the first few months of pure visual joy, I got incepted with the idea of AP. A couple years later, I am using a DSLR, a ZWO ASI 224MC and recently a TV Powermate 2.5x. These have all been incrementally improving the quality of my shots, which are planetary only for now. The big elephant in the room is that this specific OTA is not ideal for AP, especially planetary. However I am thinking of moving on to the next step, and acquiring an HEQ5, to convert and put the Dob 8" OTA on it for visual and AP. Here is where I would like your opinion. Do you think that would be a waste? I have heard that this tube being so big, heavy and bulky, would push the HEQ5 at its limits for visual, and a NO NO for AP, especially with heavy powermates and the ZWO on it. Is that true? And, assuming it is true, should I completely ditch the Dob, and focus on choosing a new better OTA? I was hoping to do that incrementally for practical and monetary reasons, for example this year doing the conversion, and 1-2 years from now getting a proper tube. However if it turns out to be a waste, I would like to avoid that path. Honest opinions will be appreciated. Thanks in advance, Alex
  21. Hi again after thinking about getting the 130p dob I think I’ve change my mind and have decided to go for the bigger 200p as I’ve realised it’s not that bad to carry after looking at some videos. As I mentioned before I don’t really have a good telescope at the moment and have never seen Galaxies or Nebulae properly before. These are my main interests and objects I’ll be observing the most ( and maybe star clusters) . I was wondering if the 200p is good for this type of thing? I live in a south facing garden ( if that matters) and relatively low light pollution.I’ve also seen filters which you can buy to get the best view out of them but not really sure how they work. Or would I be better off getting a refractor? Thanks for the help.
  22. Hello again, After a lot of you gave me some good suggestions for what my first scope should be someone had suggested the Skywatcher a heritage 130p. I just wanted to know if anyone has had this scope and would to share your opinion/experience with it. I was looking something portable and under £200 and this seems to fit. But when scopes are usually this cheap sometimes they don’t perform that well. Also I wanted to ask is having a open tube a problem for dew etc. Many Thanks, Ps (here is the original post if you have anymore suggestions) someone had mentioned
  23. Hello again, After many hours of researching and asking on forums I’ve decided not to go down the imaging road as I’ve come to realise it’s way out of my budget. Now after realising this I’ve narrowed down to three telescopes that I’m considering on getting purely for visual use.. Skywatcher 150p 150pl or the dobsonian 200p. What is the difference between the 150p and the pl? I’m after something that can let me see enough detail on planets that I’ll enjoy and also allows me to get views of deep sky objects. I have been talking to Martin from FLO as well and still can’t decide. I’m hoping you can help me make my decision. I’d also like to know how comefortable these three are as I’ll be most likely doing long sessions for sketching. My budget is £400 max. Thanks for for the help (again).
  24. (Sorry for double posting hopefully one of the mods can delete my original post) Hello all, hope you’ve all had a good week, been a few clear skies this week . In the next couple of months I’m going to be purchasing the 200p Dobsonian. And doing some research people seem to struggle carrying the ota because of how awkward it is.I was wondering if anyone has successfully put handles on it to make it easier to carry or other solutions I have found this on eBay https://www.ebay.co.uk/itm/Awning-Pole-Storage-Bag-Deluxe-Hardwearing-Holdall-/142422407055?_trksid=p2385738.m4383.l4275.c10 not sure if it’s the right dimensions I’ve also seen people suggest heavy duty trolleys. But I have to use stairs to get to the garden so that’s kind of out the question ( and might need to make a 2 minute walk to a field). Any help would be appreciated and also if possible to post me some images of what you’ve done. I don’t really want to drill in the ota to make holes for a handle.
  25. I've just received a 12" Lazy Susan bearing to see if I can ease the Azimuth movement on my 10" SkyWatcher Dob. Before I drilled any holes I thought I'd just put it in between the baseboards to see how it moved with the weight of the scope. Sure, it moves very freely and of course I'd have needed some kind of clutch to stop it flying around in the wind, but when it gets down to really fine movement, the cheep pressed steel bearing really isn't up to the job. I couldn't get the super-fine movement I had with the Teflon pads, it was just a wee bit too jerky. The Teflan pads are not as easy flowing but you get a load of control with Teflon if you apply some carefully applied muscle. That's two dob mods that haven't worked for me so far, caster wheels and now the lazy susan bearing. Next upgrade will definitely be something simple like an eyepiece.
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.