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great_bear

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About great_bear

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  1. Flocked in what way? Main tube or the inside of baffle-tube? (or both?)
  2. All good stuff above - and the definitive check as to whether you're compensating tilt error with rotation is to examine the positioning of the *shadow* of the secondary when viewed through the focuser. If your mirror is mounted centrally to the vanes (like most mass-produced scopes, and certainly the SkyWatcher ones) then offset of the secondary shadow should be in the direction of the primary like this: If on the other hand, that shadow is veering more to the top or bottom, like this: - then you've got a tilt/rotation mismatch. Hope that helps...
  3. Ultimately it's just a game of balancing the "push" of the hex screws against the "pull" of the centre-bolt. As you've (no doubt) discovered, you have to keep - shall we say - "re-asserting" the correct degree of twist of the secondary assembly in order to keep it looking circular as seen through the finder. If you simply tighten everything without doing this, the secondary can tend to do its own thing. It's a bit of a fight really - especially since the hex screws may have already ground slight dimples into the back of the mirror holder, thus influencing how it settles.
  4. Yes - that's how it's done. Whilst it can be argued that the whole assembly could be much better designed, removal is far less frequent than minor collimation tweaks so I guess it's a cost-cutting thing. I sometimes wonder if those who say that collimation is easy fully understand the subject. A full secondary collimation can be a very tricky exercise because the geometry isn't entirely straightforward and the tweaks interact. If the mirror is physically centred on the spider vanes (as it tends to be on modern scopes) then you need to offset the secondary towards the primary somewhat, which means it's not quite at 45 degrees and introduces some amount of cone error that you just have to live with. You also need to ensure that the secondary assembly doesn't get twisted relative to the focuser which is tricky since it does tend to shift as you tighten everything up - and of course, the simplistic mechanism means that all these adjustments will interact to some degree, so the process becomes iterative and time-consuming. Makes it all the more satisfying when it all comes together though! :-) - and of course subsequent adjustments are trivial in comparison.
  5. In contrast to the SkyWatcher, the Revelation 8" Dob has: Really nice high-quality Alt bearings with large tension knobs cleverly designed so that the tube just lifts straight on/off the base instantly You can fine-tune the scope balance if required Built in cooling fan with battery box Dual-speed 10:1 crayford focusser Large knurled collimation knobs on the mirror Better quality finder Decent (re-sellable) eyepieces with 2" extender tube
  6. I have a Mak 180 and the Revelation 200 Dob (which is better than the SkyWatcher one). The Dob is now my travel scope (seriously). The OTA fits into the roofbox on the car, and the dob base has no impact on space for me as I pack luggage bags both into and around it in the car boot. I bought it because: 1. It is considerably more stable in a breeze than a tripod-based scope - this is a big plus 2. It is considerably less hassle to set up and use than a motorised setup Il still use the Mak for those long urban nights binoviewing Saturn, Jupiter, or the moon etc. - but it is staying at home from now on. Life's too short for all the faff setting it up when visiting a dark sky site. The Dob feels like freedom - and the wide-field views are breathtaking!
  7. http://www.telescopehouse.com/cgi-bin/sh000001.pl?REFPAGE=http%3a%2f%2fwww%2etelescopehouse%2ecom%2f&WD=winged&PN=Orion_Winged_Rubber_Eyeguard_1_25__%2ehtml%23a07406#a07406 Sent from my SM-A300FU using Tapatalk
  8. ...I can't help but think the four photos on this guys ABS scope advert here <click>, somehow don't quite do justice to the size of the thing as seen here <click> Made me smile at least, on this very rainy day
  9. Yup - a sheet of white paper (with some Sellotaped-on string for easy retrieval) lightly wedged between secondary and primary. If rotated properly the secondary will present a white circle when peering into the drawtube, if not, it appears as an oval. It's also a good opportunity to check that the circle thus presented is positioned centrally relative to the drawtube.
  10. Apples and Pears really. I've moved away from Plossls / Orthos. I now settled on Long Eye Relief eyepieces (mainly Delos) for the following reasons: They are more comfortable to use than classic designsThey are *much* less affected by dirt and greaseThey are considerably less likely to get dirty in the first placeThey are easier to clean once they do get dirtyThe image projection feels more "cinematic"Now I've had the 4.5mm TMB Planetary II for about 6 weeks, I'd say the issues with it are the expected ones, namely: The dancing ghost reflection Stray light control issue (actually caused by the Smyth lens inner retaining ring)With regard to issue #1 above, I can live with this. With regard to issue #2, this definitely needs fixing. However, the problem is not the inner barrel baffling (as is often supposed), but the inside retaining ring for the Smyth lens. It has a matt black bevelled edge that is still quite reflective, machined at such an angle as to invite such reflections. It should be possible to fix it by attaching a circular, slightly conical piece of self-adhesive flocking paper (like an A4 paper hole-punch reinforcement ring, but black and in miniature) but it will take time to create the perfect shape and size to fit. Definitely do-able though - and will be well-worth the effort - on my to-do list...
  11. Well, the nice thing about an F13 scope on a motorised mount is that any respectable simple-design eyepiece will give you top-class results on the planets. For planetary use in such a scope I'd avoid TMBs / BSTs, and at F13 Meade 4000 Plossls will give results indistinguishable from Tele Vues at minimal cost. I'd take both the 9.7 and 12.4mm Series 4000 plossls over any one BST eyepiece for use in your scope (I've owned a Sky-Watcher 90mm before). But preferences vary of course... :-)
  12. Ah yes - where all my light pollution comes from
  13. That's not quite right. There are no "cheap clones" - this style of eyepieces all come from the original manufacturer. The dispute was over who had the right to sell, and under what branding. Since none of us are party to what was agreed in the contract in terms of minimum order size, penalties, redress, etc. etc., it's not our place to judge in absence of facts, but what we do know, is that additional focal lengths were added independently by the manufacturer. For the "inbetween" new lengths at the shorter end of the scale, these are likely to be fine (as these are neg-pos designs, 0.5mm - 1.0mm difference can probably be subtracted simply by lengthening the barrel, with no lens modifications and no adverse optical effects). Scaling the design above 9mm however is a little dubious... EdZ on cloudynights asserted that in resolution tests, the eyepieces scored very favourably. People's subjective experiences of these eyepieces however, vary considerably.
  14. You may find 8mm is pushing an F13 scope a little too far - it's certainly pushing past the edge of maximum resolution.
  15. When you say "offered" do you mean for free, or to buy - and if so, how much?
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