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johninderby

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Everything posted by johninderby

  1. I think I'll just stick to the articles that I've read by Roland Christen, James Mulherin etc. John
  2. I think that the second-hand value of the basic OO dobs/Newts may be hurt, but the better scopes will go up. As OO moves up-market if a second hand dob/Newt has the same specs as latest VX model available on the OO website it will pull-up the value of the second hand scope. John
  3. OO's PV ratings for their different grades of mirrors are actually better than the stated ratings. IE their 1/4 PV mirror will usually be around 1/5 PV actual and the 1/6PV around 1/7 PV actual etc. Only laser interferometry certificates are worth the paper they're written on (assuming the test is conducted properly of course). Any other method is subject to a fair bit of error due to the limited number of sample points on the mirror and also mechanical error in the measuring process and will usually over-estimate the quality of the mirror. There's some good info on the Optical Mechanics websi
  4. Would this do? Stainless steel strips 0.5mm thick up to 200mm long and 9mm to 25mm wide http://cgi.ebay.co.uk/Polished-Stainless-Strips-0-5mm-Exhaust-Bracket-/160502689226?pt=UK_Motorcycle_Parts&hash=item255eb4adca John
  5. OO is definitely moving up-market and away from a lot of the mass market stuff. From statements made by Barry I know that OO were struggling to keep up with demand for their new top-end scopes and so it's a sound business decision to concentrate on the more profitable end of the business. I had wondered why they were bothering making the basic dobs/Newts when SkyWatcher etc. were selling mass-produced scopes with machine made optics that were almost as good as the standard 1/4PV OO optics. John
  6. It's 20" and the regular version will be f/6.8. I believe that they're special order at the moment but will be added to OO's website early next year. The ODK16 is the biggest listed on OO's website at the moment. OO is also building two of the ODK20s of a slightly different spec optimised for infrared for the ESO and they'll be used at the Paranal Observatory in Chile. I don't know what they'll sell for, but I'm sure it'll be way put of my price range. John
  7. Came across this link on the OO Yahoo group about a customers visit to OO to see their ODK20 being built. Some great photos of the scope as well as the optics being made. I'm not sure weather to admire this 20" scope or just feel very, very jealous. Click on "Toutes les News" on the left of the page and then on the first news item. http://www.felopaul.com/ John
  8. Worth looking at these links Re: the Telescope Service 90mm Triplet APO. Bit more expensive than the Megrez 90 but better optics. http://stargazerslounge.com/members-equipment-gallery/113169-ts-apo-triplet-90mm-f600.html http://stargazerslounge.com/equipment-reviews/116280-ts-apo-triplet-90mm-f600-experiences.html John
  9. The Omni Plossl is not too bad, but no better than most of the other low priced plossls out there. The TS 15mm will be sharper and will have clearer colour rendition so yes it's a step up optically. John
  10. While the 15mm isn't quite as sharp and contrasty as the clones up to 9mm and there is that bit of edge distortion it's still a decent eyepiece. I've kept mine as an inexpensive eyepiece to have around, and it usually gets left in the scope to use for a first look. If I want to get a bit more serious I drag out my 13mm Ethos. John
  11. Skies the Limit does the 15, 20 and 25mm in their version of the TMB clones, although I'm not sure if they should really be called TMB clones as the original design wasn't intended to go to those focal lengths. I bought all three and tried them out in a f/6 scope. The 15mm was not bad at all, but had some edge distortion. The 20mm had a bit more edge distortion, but was still usable in an f/6 scope although it would be better in a slow scope. The 25mm had quite a lot of edge distortion (from about 50% from the centre) and I'd only recommend it in a slow scope such as an SCT or Mak. BTW I kept
  12. Ace Astronomical still has the 8mm Ethos at £399.00 so I wouldn't pay much over £300.00 second hand. John
  13. I wonder how much over £300.00 it will go for? John
  14. I think you're wise to go with the Revelation diagonal. I've not actually seen a bad one yet, it's just that some are a bit sharper than others. And of course if you buy from a good dealer it could always be returned if necessary. John
  15. Generally it's the build quality that's the biggest difference in the more expensive diagonals. In particular the mounting of the mirror and how accurately it's collimated, and also it's ability to maintain collimation if knocked. The mirrors themselves are also more accurately made and the coatings are better and more durable, but assuming that the cheaper diagonal is properly collimated the difference is small, at least that is when they're brand new. I've used the Revelation Quartz diagonal and it was very, very good and I couldn't tell any difference optically between it and a WO dielectri
  16. Optically there's not much to choose between them. However the SkyWatcher truss system is so much easier to setup and use than the LB that the SkyWatcher gets my vote if you're looking for a truss type dob. Up to 10" I'd suggest going with a solid tube dob. Its only when you get to 12" that the truss's advantage of collapsing to a smaller size becomes really worthwhile. BTW the SkyWatcher truss dobs are slightly heavier than the solid tube versions. The truss mechanism weighs more than the equivalent length of solid tube it replaces. John
  17. If you're using the TS curved base plate when you tighten up the mounting bolts it will tend to pull the tube wall up against the base plate so there may be no gap. If there is still a small gap some thin very soft weather-seal foam tape (the 10mm wide by 6mm thick stuff) down each side will do. You don't want a big piece of 5mm mouse mat type foam under the whole base plate as when tightened down the base plate will have a small amount of movement. John
  18. On one hand it's far too much to spend on a focuser, but then again the first time I used it I couldn't help thinking it was worth every penny. It really is that good. John
  19. You won't be disappointed with the Revelation crayford. It may need some minor adjusting to get the very best out of it, but it's still amazing value for money. As you go up in cost focusers will be more precisely made, smoother and able to handle more weight. While Moonlites are very nice, they're still not the best available. A Feather Touch rack & pinion focuser is more precise, smoother and able to handle a lot more weight than a Moonlite, but unfortunately it's also about £600.00. Whatever you do never try a Feather Touch R&P focuser. I did and look what ended up on my FLT98. J
  20. Revelation focuser with Scopes'n'Skies baseplate on a SkyWatcher 250PX dob. John BTW changed the focuser knobs for some SkyWatcher ones I just happened to have.
  21. Nice report Olly. Reminds me of my first light with my Lunt 60. I too find the standard focuser is up to the job, even if it's not as nice as a Feather Touch of course. Curse the FT R&P for spoiling me. BTW I found the Pentax XF Zoom 6.5 to 19.5 to be the best eyepiece for the Lunt. Just as sharp and contrasty as a Baader GO, but with the ability to set the mag to just the right mag. John
  22. Forget the first two focusers. There about the cheapest of the crayford type and not exactly top quality. The Revelation is a good mid-range focuser with far better build quality than the first two. I've used/owned a few of them and have been very pleased with them. Definitely a "Best Buy". You have to spend quite a bit more to get a better focuser. You can get a SkyWatcher type baseplate from Scopes'n'Skies Astroboot for £2.00 that will make the Revelation a direct bolt on replacement on a SkyWatcher Newt/Dob. John Edit: Scopes'n'Skies has taken their Astroboot offline for a few weeks.
  23. I think I see what you're getting at, but it still might be a bit tight for the drawtube to pass through. You know rather than thinking in terms of a square hole why not an octagonal one. Should be easy enough to cut with the Dremel. John
  24. The problem with cutting a square hole is that where you want to drill the mounting holes for the base may end up being within area of the cut-out, or leave the mounting holes right on the edge of the cut-out. Also as mentioned in an earlier post using a hole cutter is not recommended. While it can be done with the right preparations it's easier and quicker just to drill the holes. Attempting to drill the hole with a hole cutter in this situation could land you in A&E sooooo easily. John
  25. That makes it a little more complicated but still not a big problem. Cover the area around the focuser with masking tape. Then using a piece of A4 paper held against the tube ring on the end of the tube to give you a right angle, draw lines along the tube to mark the outside edges of the existing focuser hole. Then using these reference lines draw new lines along the tube for the hole size that you're going to cut out. Then a couple of marks to set the distance of the new hole down from the end of the tube. Place the new base in position and mark out the hole and the bolt positions. You can u
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