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ianmwatson

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Everything posted by ianmwatson

  1. you can imagine the eyepiece as a magnifying glass with which you are inspecting the real image created by your objective/primary mirror. as do magnifying glasses, different focal length eyepieces will give different magnifications. in addition to the primer highlighted by andrew, i think there's a good one over on the televue site.
  2. Ok Wayne, that's interesting. Is it a parallel, serial or USB controlled SC1? (in addition to the pre-existing USB cable). It is the parallel version I have made. Have you tried manually setting D0 to 0 with port commander? The screen should go black. I have heard that setting your frame rate to 5fps before hitting LE works for some, have you tried that? It didn't work for me, might for you.
  3. I have completed my vesta sc1 mod, complete with a replacement mono ccd. It all works great, including the raw mod, so should be a sensitive guide cam. It was fairly cheap, £18 for the camera off ebay, £35 for the ccd from bernard @ modern astronomy and about £2 for the nand chip, holder and resistors. I have a snag though, it works well with W98 SE & k3ccd but drops quite a few LE shots with XP & k3ccd. I am using the XP driver for the vesta. Curiously when I set logic with port commander it works in XP, so I am assuming it's a software glitch. Anybody shared this problem? Maybe found a solution? I've tried QCUIAG, some seem to have a similar problem.
  4. The radial offset isn't, it must be calculated and engineered into the tube assembly. As you say though, the axial offset is automatically set due to the collimation process. As discussed though, radial offset isn't really worth worrying about in slower scopes.
  5. Especially if you have a slower scope, like F6 or F8.
  6. All good points regarding the offset. One other thing worth checking if you have problems in future is the laser itself. I made a vee block for mine, if you position the laser collimator in the block and mark the fall of the laser on an opposite wall, then turn the laser through 180 degrees and mark the fall again you may see that the laser isn't true to the holder. I had to adjust mine from the box, it was out by 5 inches! It was a fairly familiar adjustment though, 3 screws, and didn't take long at all. For a super accurate collimation you can't beat collimating the diffraction rings.
  7. I was just about to unintentionally repeat tiny's post. I love my ethos too, and i have the comfort of knowing it cost me 50p more than the scope and mount that's currently attached to it (the C6-S, CG5). Anyway, I hope you enjoy viewing your new diagonal, I mean the view through your new diagonal.
  8. It's normal. The Earth rotates with regard to the stars once every sidereal day (it is not quite 24 hours, but that's not important right now). So your motor is doing the same, but in the opposite direction, thus tracking the point you have your scope on (this all depends on a reasonably accurate polar alignment). This movement is in RA (right ascension). It must be RA because if you consider the co-ordinates of an object at the zenith it's declination is always the same (for a given latitude), but the RA changes through the night.
  9. I think the eye relief is actually increased in some cases. The panoptic 35mm is unusable in a regular barlow without the special pan-barlow adapter wotsit. You could check out the TMB planetary range, they go from 3.2mm to 9mm I think, maybe there's a 2.5mm, can't remember. SCS Astro used to do them. The snag with plossls is the eye relief is proportional to 70% of the focal length. So a 10mm gives around 7mm. Orthoscopics have very marginally more, 90% ish, but are still tight.
  10. I never did find out what the plastic bit was about, oh well it sounds like you got it sorted.
  11. I'm pretty sure they are the same mount, as is the Vixen GP. I think you might be able to get the spares from Celestron USA, don't quote me though. Is it one of those flat round (annular) type rings made from teflon maybe? I have some in my old super polaris, they are about 1mm thick. As for the manual, try google'ing vixen gp manual. That should help you out.
  12. Pete, it sure is like a minefield. Although as long as your scope is quite well collimated it'll be fine. I use a laser collimator, spending about 2-5 minutes on collimation before use, after the cool down time. Although reflectors aren't necessarily the best for planets, I managed to snag saturn with a webcam with it (my sig caption). Don't forget to collimate your collimator though. Don't ask (-:
  13. An example of what coma does to reflectors, the diffraction limited field of view of my 8" F6 reflector is about 4.5 minutes of arc, not much is it?. This figure would go down even more as the F ratio goes down and infact go down as the aperture increases due to collimation tolerances becoming tighter and therefore the chance of achieving collimation reducing.
  14. Good point Gaz, I wonder in what way the plossls are lacking. I used to use vixen lvws in my F6 reflector, they were very well corrected with a pretty flat field. Hyperions maybe? If you could break the bank a little then I suppose there's panoptics.
  15. Hello, I have a celestron 6" sct and an ethos. I also have a 2" william optics diagonal, i had to buy a sct screw in adapter though. In my case I removed the visual back it came fitted with and ditched it. Then fitted the diagonal with screw in adapter directly to the rear of the scope (it's what's left when you unscrew the visual back, should be around 2" diameter). If you haven't already got a 2" diagonal for a refractor or whatever you can buy one ready to go on your sct, as others have said. Couldn't you just remove one screw from the existing diagonal though? Having said that, you're right to worry about security. I didn't understand why you said the part had to be plastic.
  16. I'm not sure that would be astigmatism John. More likely coma from the mirror. The on axis sweet spot of an F4 mirror is pretty small. Any minute lack of accurate collimation would be indicated also. A coma corrector might be worth consideration. Also, televue test their optics at F4 so should give good results. Just my 2p.
  17. Agreed, with poor quality barlows. If you use one of the good quality ones, televue 2x or 3x springs to mind I don't believe you will see a perceptable difference, well I don't anyway. I have used a 2x with an ethos to split polaris through my 80mm refractor, perhaps not a huge challenge but when you consider how many chunks of glass there are it goes to show how well coated the barlow must be. The ortho doesn't need many chunks of glass because it only yields on average 40 degrees so doesn't have to correct such a wide field. It's fair to say however that its performance in scopes faster than F6 isn't superb, enter the barlow. When all is said and done I asked why a person might not bother with a barlow, and Gaz I take your point. And maybe the question is why bother doing it? So, I suppose there's 2 reasons, to yield longer eye relief or increase the effective F ratio of a fast scope.
  18. Ian, why would you not barlow orthos? If you did you'd get more eye relief and I can't see an ortho vignetting somehow.
  19. Agree with the orthos, and possibly televue plossls, the eye relief is tightish though. IIRC it's a scaled design and the eye relief is 70% of the focal length. I'd probably go with a good quality barlow too.
  20. I'm a previous customer, didn't get an email. I got my ethos on the november 10% offer.
  21. Missed that one, where was it advertised?
  22. You can get away with a spherical mirror, but why would you, when even a slow scope will perform better with a parabolic mirror? You can buy a mirror kit, and grind a parabolic mirror, or buy a parabolic mirror, or just buy a telescope with a parabolic mirror and start looking through it right away. I seem to remember reading that a spherical mirror slower than F10 was diffraction limited, so would perform equal to a mass produced parabolic mirror. My point wasn't that I would or anyone should, it was that it could
  23. Sorry for the late reply. I did notice some, it was mine though. The eyepiece seemed pretty clean, a little field curvature was the only thing I saw.
  24. The next step is to make sure there's somewhere to attach the rail, if not you will likely need tube rings also.
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