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Found 13 results

  1. 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.
  2. Ordered my Altair Astro 6" RC and quickly arrived (I got it shipped as I was away for few days). I know this same design is created by GSO and sold rebranded my others, but I decided to go for Altair Astro one because they're just nearby and it seemed the best value for quality, arriving with double dovetail (fundamental to keep the optical axes linear), better focuser, and all the needed extension rings. The scope arrived perfectly packed. As I knew collimation could be a problem, I brought it to the shop to get it checked in case of big collimation problems and to get some advice. First light was on Moon and was great even if visually with some powerful eyepieces I had impression it was probably needing some tweak to collimation. First pics were of the sun with Kendrick solar filter, and they were quite good even if again I felt was probably going to need some more collimation. I don't use any focal reducer or field flattener with it, and I have a Nikon D750 full frame, so I know I'm testing it a lot in particular on the edges. Anyway first night out and some test shots and star test, I got quickly frustrated being not able to correctly collimate, most of all because on the internet I found tons of different procedures. I actually posted all process on SGL and you can check it all, including final victory arrived quickly following simple suggestions provided by AA: http://stargazerslounge.com/topic/249532-altair-astro-6-rc-collimation-help-needed/?p=2720144 Now that is collimated, and after a full session and a few days using it, I can say that the scope is very solid and well assembled. Surely it looks and feels much more expensive than what it is. With my D750 and the provided focuser there's basically no flex, the baffling looks excellent and there's no stray light entering. I have to be honest I'm really surprised by the quality of the scope, for the cost I'm absolutely satisfied, compared to even more expensive refractor(s) I had in the past from William Optics and Skywatcher. No plastic or cheap or loose parts, all metal and solid, seems and feels to be built to last forever. Like everyone I think that initially the collimation process can be daunting and discouraging for new comers (I never did it before), and it's indeed crucial to get perfectly sharp images. The scope is better built for non full frame DSLR or CCD, but even with my full frame I can use easily up to 70% of the central image, and that is a lot of resolution, details and light with my 24 megapixel full frame! Despite what many said I did not find the f/9 particularly problematic, even visually is absolutely stunning on DSO as well as on Moon or Sun. I use high quality Baader eyepieces (24,17,5), all on the 2" focuser with a 2" diagonal, and the views are great. Surely a more open aperture would be better visually (doesn't matter imaging with a noiseless camera like the D750), but I noticed it did not really made such a huge difference with my F/5 Startravel150. If anything everything looked much sharper and detailed, no aberrations whatsoever, fantastic. I also did not notice any difference in contrast despite the central obstruction of the secondary, if compared to my ST150 big refractor. All in all a fantastic instrument, it feels 'professional' and the process of collimating makes you feel it's more yours in the end. I have to say that once you go past the collimation, is by far the best quality you can buy for the money, without the aberrations you get on other configurations, and without problems of dew etc. (I have my dew strip on the guider but nothing on the RC, no need at all even after hours pointing directly up in a very humid night). Looking forward to spend many nights with this great little monster of quality!
  3. Hi there guys, realise it’s probably a bit of a long shot, but I’m hoping that someone on Stargazers is looking to part with an Altair Astro Starbase. Have my heart set on one of these as the ideal future proof tripod for my field observing platform. Paul.
  4. This is a 6" f/5.9 refractor (890mm focal length). It is constructed from high quality Japanese Ohara and German Schott glass with top quality coatings. This has the large 3" rotatable focuser. It can accept a 2" or a 1.25" diagonal. It comes with a carrying handle and a vixen dovetail bar. As you can see there is some of the usual scuffing on the dovetail bar. No doubt you have seen the reviews of this scope. We have gone a bit berzerk over the last few months and have run out of scope shelves, so this one needs to go. We bought it new around 18 months ago direct from Altair Astro. It has seen minimal use what with one thing or another. £590 preferably by bank transfer. The box and packing material has gone the way of all things. As such, this would need to be collected. I don't mind driving to meet someone half-way if necessary.
  5. ........., and two come along at the same time! Arrived back home after been away for work all week to find that finally my new Televue 2.5 x Power Mate had at last arrived (ordered way back in early August from Orion Optics), along with a second hand Altair Astro 3x Barlow I bought off a member on here (thanks Paul! ) . So now I just need some clear skies to test both these new additions to my Astro kit out. Not looking good for tonight over here, but hoping at some point over the weekend, or at worst early part of next week to give them some first light. Be interesting to note any real difference between the two barlows, other than the magnification of course, with the Televue costing considerably times more than the Altair Astro 3 x Barlow!
  6. The postman, well DHL delivery guy, bought a few sizeable packages this morning. After waiting a month for an AYO II from Switzerland, only to find out it was going to be another 4-5 weeks lead time, I had to cancel the order as I am currently mountless and booked in for the SWAG Star Party end of March. Instead, I placed an order for an Altair Sabre V2 with dual vixen saddles from Harrison telescopes which were all in stock. I also took advantage of the Celestron spring sale and thanks to the guys @FLO for splitting out a C8 Evolution OTA for me. I could have had a standard C8 but I lke the silver OTA colour and "Evolution" sounds, well...cool. To go with it I added an Astrozap Flexi-heat dew shield and SCT adapter for my 2" Altair diagonal. The Sabre, saddles, C8 and dew shield all arrived safely together this morning I already have a Celestron CG5 2" tripod waiting at home so hope to be building up a nice manual alt/az, dual scope setup this evening. Initial impressions of the Sabre are good. The clear anodised finish is not quite as nice as I'd hoped, it's rather dull, but the machining is very nice. Both axis are smooth although there's a little stiction, but I'm sure that will vanish with the weight of the scopes. It's quite a lump to handle, more so than I'd imagined. I don't think it will qualify as grab and go with a C8 and ST120 mounted and attached to the CG5 tripod. The Altair vixen saddles are very nice indeed, finished in black with the Altair logo machined in. The clamp knobs are chunky and when turned, the clamp glides smoothly in on a Teflon washer and is sprung out, for removal of OTA without having to slide the dovetail through the clamp. I would apologise for the impending cloudiness, but quite frankly someone else must have made one hell of a purchase a few weeks ago to bring on the current permacloud Watch this space for pics.
  7. Has anyone tried the Altair Astro 80ED Triplet with the Altair Astro PlanoStar 3" 0.79x 3-Element Focal Reducer? I cannot obtain the Altair Astro PlanoStar 2" 0.79x 3-Element Focal Reducer, which is Altair Astro's preferred option for my scope - Nil stock. I can, however, obtain the more expensive 3" version which would certainly eliminate any tendency for vignetting on the QHY8 Pro chip. I just need to know if the focal reducer will give a good flat field. Steve
  8. Since the foundations went in last weekend, it's about time I stuck the pier on it. First problem was that although the concrete was levelled before the bolts were put in, putting in the bolts un-levelled it quite a bit. So balancing the pier as best I can, it's still got a noticeable lean. I didn't have a spirit level so had to use a tablet, which showed it was about 1 degree off vertical - the photo makes it look worse as the camera has quite some optical distortion to it. I'm thinking I could get some washers to pack under it to level it off? The instructions for this pier say it doesn't have to be perfectly level, since the levelling can be done on the top plate, but I want to do this for cosmetic reasons. And here it is with the EQ6 stuck on it. According to the bubble there's a slight offset from level, but I'll do that more accurately later. I don't have a spanner big enough for the levelling nuts anyway so it's just finger tight for now. Hopefully the few clouds will go soon, and I'll get it rough polar aligned and start imaging the moon...
  9. M13 is now modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Telescopic views reveal the spectacular cluster's hundreds of thousands of stars. At a distance of 25,000 light-years, the cluster stars crowd into a region 150 light-years in diameter, but approaching the cluster core upwards of 100 stars could be contained in a cube just 3 light-years on a side. For comparison, the closest star to the Sun is over 4 light-years away TELESCOPE: ALTAIR ASTRO RC 250 TT MOUNT: IOPTRON CEM60 CCD: QSI 690 CCD LUM 3 X 500 SECONDS RGB 3 X 500 SECONDS TAKEN FROM LONDON DATE 18/04/2015 FULL RES https://www.flickr.com/photos/95267225@N06/17198672512/
  10. Hi all, I finally got my hands on my new Altair Astro RC 6" and my new full frame Nikon D750! I updated all my software, tested all connections (BackyardNikon, EQMOD, Astrotortilla, CdC etc.), all working and nice So I got a first test image to check collimation...and what I feared happened, that is I need to collimate the scope! This first 30 secs image of M13 shows obvious stars problems: So I decided to do a star test (defocused star Arcturus as Vega was covered at first), and this was the result: And I said ok...not really collimated, I need to adjust the secondary, and using my camera's liveview maximum power (out and in focus were out the same), I started trying to guess/adjust things a bit, and after it seemed to be better (small movments and recentering the star every time), I took another pic of same M13: It looked definitely better down right, but worse elsewhere...overall an improvement, center at least is good, but not so much, so I went on tweaking more on the star test but moving on Vega (Arcturus was now too low and covered by some clouds). After some adjusting on secondary mirror, and with clouds now gathering, I took another example shot (all 30sec iso 6400 to have consistency): And it looked again that I'm 'moving around' the problem, but never getting it properly right...so I decided to take another pic of the star test on Vega. Overexposed as I forgot to reduce exposition, but in the 'reflections' the secondary is still visibly de-centered, maybe slightly less, maybe in a different direction...I'm not sure: So before clouds completely covered the sky, I tweaked it a bit more and took this final test shot: Now the question is....I have a feeling I'm shooting in the dark, center is pretty much ok but I cannot seem to get decent collimation results, considering I want a quite good one. All I have is a normal collimation laser (the red one I cannot afford the more expensive green one), that seems decently collimated, and I got it today to test it. And then when sky is clear I get a star test. I'm looking for some help for a down to earth approach working with these simple tools? I've read a lot but there are many different ways and opinions, too much talking about theories and useless stuff, while I wonder if someone with a similar scope have found a simple way to collimate, meaning I can spend all the time and patience but cannot afford too expensive tools at the moment. Anyone with experience can tell me what I'm doing wrong based on these pics and how to improve my procedure to collimate? Possibly also during the day considering that clear nights are rare so I'd rather do it during the day and just verify it later As I said I know there are various degrees of perfection, I'm not looking to get it perfect right away but at least to know how to achieve the best I can, how am I doing now, how to do it better etc. Thanks!!
  11. Hi there, I am contemplating getting an 80mm scope to replace my existing 9x50mm RACI finderscope. However this got me thinking about how to mount the 80mm scope onto the Edge. Dual dovetail plates are out, because I use a Kendrick ZapCap and I don't fancy cutting a section out to accommodate another dovetail bar. I really like the look of the Altair Astro ultralight guidescope rings. Has anybody ever mounted these to an SCT using the existing attachment points on the rear mirror cell?
  12. Hi I am looking to purchase a second hand Altair Astro Sabre II With Vixen clamps as a grabngo alternative to my goto GEM setup. In the end decided to buy new direct from Altair Astro.
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