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Everything posted by sheeprug

  1. Thanks Nebula. Intereswting your comments about fans. The OO14" mount does have a fan, but it's actually a rather puny thing. I'm feeling rather tempted to beef it up a little. On the other hand, the primary did get a little dew on it the other night, so it can't be too warm! SR
  2. Thanks for taking the time to reply Mike. There's some interesting thoughts there, particularly about the type of ground. I'm setting up on my patio at the moment, so if concrete slabs take a lot of time to cool down that might be an issue. SR.
  3. Thanks Dave, All I've added a Baader 2.25x barlow to my armory, giving me new magnifications of 330x an 540x. Looking at polaris last night if I de-focused slightly I could see a reasonably neat doughnut showing the collimation was pretty close, but here was too much disturbance to see any diffraction rings. This did improve as the night went on (mirror cooling down?). Later i moved to try splitting the doubles in epsilon lyrae, which were more or less overhead. I couldn't quite split them cleanly due to, i think, the atmospheric conditions. On the other hand, it might be the limit of the scope - it's a 1/4 PV mirror. So, a couple of questions: 1. are there any websites out there which predict/forecast/monitor seeing conditions? At this stage I'n not clear what good or bad seeing conditions look like. 2. is it possible to relate mirror specifications to telescope resolution? I'm assuming yes, but it's probably very complicated. If anybody else out there has similar quality mirrors it would be interesting to see what resolution you achieve.
  4. Thanks Dave. That sounds more sensible, but the way I read it you needed to use the high magnifications to see the diffraction patterns properly? SR.
  5. As people might have noticed from my recent welcome message, I'm getting somewhat disappointing resolution from my Orion Optics 14" dob. I rather suspect it's a collimation issue, though I've set it up with a cheshire pretty well - to my untrained eye at any rate. However, it does look like there's a little coma and astigmatism. The mirror is stamped at 1/4 pv. So I'm wondering if trying the sort of star testing described here might be worth trying: http://www.backyardastronomy.com/Backyard_Astronomy/Downloads_files/Appendix%20A-Testing.pdf or http://www.telescope-optics.net/star_testing_telescope.htm It also looks like a pretty useful sort of skill to acquire. Big problem is the necessary magnification: 40-50 x the aperture in inches. That's 560x to 700x for my scope. I can't imagine i'd use that in normal use (how do you track a dob at 700x?), but a 3x barlow would get me to that range with my current eyepieces. So, question is does star testing work in our skys in the UK. Do many people use it, or is the atmosphere usually too disturbed. And if so, is it worth splashing out on a 3x barlow which would give me magnifications i'd probably very rarely use for normal viewing. Or should I try some other collimaion technique? Best, SR.
  6. sheeprug


    Quite, but I think it's probably down to getting the collimation right. Currently my EPs don't give me enough magnification to do any proper star tests,so a 3x barlow is next on the shopping list. SR
  7. Thanks Dave, Interesting thread. As I read it though, the Bresser SA and the ES focal extender operate on similar principles to the Powermate and so are not simple barlows. So i'm sort of looking at them as Powermates on the cheap. So if they work well then why spend more - though i do admit that were money no object TV throughout would be nice. Peter
  8. Hi All, Apologies for yet another barlow thread, but has anybody got any experiences to share with the Bresser SA barlows? Also, are there any UK suppliers for the ES focal extender,s which I gather are well thought of? I hate buying things twice, so I'm sort of tempted towards a 2.5x Powermate, but that's a lot of extra budget if the alternatives do a good job. My other lenses are ES 24,11,6,7. SR
  9. sheeprug


    Thanks Chris (and others too) for the welcome. It's been a bit of a learning process! As bought used, the mirror was really filthy, so eventually I picked up courage to clean it. This went well, but I ended up pinching it when I put it back - lovely triangular stars! After loosening the mirror cell screws this improved , but I then found the springs on the primary collimation screws didn't keep the mirror stable. I then realised there should be some locking screws, which were missing - presumably explaining why it didn't hold collimation very well. (I'm using a cheshire by the way). So I'm much happier now, but I think my next acquisition will be a powermate x2.5 so I can get sufficient magnification to try some star tests. SR
  10. sheeprug


    Having been lurking here for a few months and enjoyed many of the postsI suppose i better decloak and say hello. Hello! Right - that's that done. :-) About me: well, a long time interest in astronomy, but not really done anything about it until recently when an Orion Optics 14" dobsonian came my way. Prior to this I'd borrowed a small Meade ETX and decided (1) aperture was everything and (2) a decent finder scope was vital. Interests? Well everything really, though I do particularly like DSOs. Current pre-occupation is getting the dob working well. It's a great light gatherer, but i'm not quite getting the resolution i'd like - e.g. i can't quite split the doubles in epsilon lyrae. Despite my best collimation efforts I'm still getting some coma and astigmatism. It's a 1/4 PV mirror. I'm based in a small village in Suffolk (nearest town is Woodbridge), light is not too bad - milky way is just about visible on a good night. Sheeprug.
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