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Everything posted by brianb

  1. There's a transit of Venus next year (early June) but it's very badly timed for observation from the UK. Western America / Northern Pacific / East Asia is good. Mercury transit is not on my radar ATM - the next is 2016 IIRC.
  2. brianb


    Congratulations! 1) Has the barlow been through the dog? 2) Is the elusive Hiigs boson also hiding in your dog's bed?
  3. No. Pinholes may exist in the manufactured product, but as there are 2 layers of ND 2.5 the chance of direct light getting through are very remote. Age deterioration is more likely to be splits or tears due to deterioration of the plastic film with continued exposure to UV light (it will eventually go brittle).
  4. Nice capture of the filament field!
  5. Sorry but I never heard of faint objects being made more visible by reducing the aperture. If you're getting a "contrast improvement" maybe it's because the full aperture view is too bright - a filter would have a similar effect without wrecking the resolution. Alternatively it's because your reflector is not properly collimated or nowhere near in thermal equilibrium with the environment - no scope will perform to its potential under these conditions, but longer focal rations do tend to give a tider (but not better resolved) image in poor conditions. That's true, but there's less information in the stopped down image - much less, unless the optics are of very poor quality (unusual these days).
  6. Thanks guys ... new processing style is just less aggressive wavelets ... Here's a CaK full disk mosaic. 2011 Apr 26, 1029-1033 UT. William Optics FLT 110, prime focus, Lunt B1200 CaK diagonal, DMK41 - 6 frame mosaic, 50% resize; full size version.
  7. If you want to go to the same place lots of times, set it up in the user object list. Otherwise just look up the RA & Dec and use the "goto" to slew to those coordinates - most have a mode where you just punch in the RA & Dec but with all of them you can view the coordinates you're pointed at & slew around till you get to the values you want, or recognise the field. A visual (live view or eyepiece) crosscheck of the field with a chart or previous image is required in any case, numbers can get entered incorrectly or the scope may not be pointing exactly where the computer thinks it is (this can be a particular issue when imaging at long focal lengths).
  8. A mosaic of the activity near the meridian in the southern hemisphere. AR 11196 has lots of bright plage but only a few tiny spots; AR 11195 has many spots but not much plage. 2011 Apr 26, 1100 UT. William Optics FLT 110, 2x Powermate, Solarscope SF-100 Ha filter set, DMK41 (2 frame mosaic). Transparency good, seeing rather poor with condiserable boiling. I've gone for a slightly softer / more subtle processing style; please tell me if you like / hate it (constructive criticism always welcome!)
  9. Very nice Olly! Yes, solar seeing is often at its best when the sun is pretty low in the morning sky, before the heating starts to get the thermals roiling away ...
  10. I very much doubt it - and, if so, an ordinary moon filter will fix the problem.
  11. Secondary obstruction has less effect than almost anyone imagines ... the worst effect is a slight reduction in contrast, which is critical for planetary work, yet all the world class planetary imagers are using scopes with central obstructions, many of then SCTs with 33% or more CO. Optical quality has far more effect on the diffraction pattern than central obstruction. You pay for good optics! Refractors do work a bit better than reflectors of equal aperture when out of thermal equilibrium, but that's because of the number of times the light goes up & down the tube, not the central obstruction.
  12. Really nice ... what sort of exposure time were you getting with the Flea?
  13. In my experience you need 4"+ to have much hope of seeing true "rice grain" granulation visually. The seeing isn't always good enough for that much aperture to be useful - but just occasionally you will get gains with increases of aperture well beyond 10".
  14. You should have enough material to make both full aperture and off-axis filters. You'll probably find the full aperture filter works better about 8 days out of 10 ... especially if you use a deep red (Wratten 29 or deep sky Ha) filter in the eyepiece to help steady the seeing.
  15. Nice images there! Seeing must have been quite steady to get away with 2.5x ... especially with substandard transparency.
  16. No I don't know the whole sky - I have almost no knowledge of the stuff south of declination 20 deg South - but otherwise I'm pretty happy that anything "out of place" which is easily visible will be spotted and can find my direction from a random patch of clear sky. I don't even "know" all the constellation "figures" but I do know more than enough to be able to find my way around even in sparse areas like Camelopardalis and Leo Minor. You can easily get away with a lot less than I know - and you will continue to learn, if you star hop rather than always relying on goto scopes to find objects for you. You'd probably be surprised how many professional astronomers can't find quite easy constellations like Perseus!
  17. You shouldn't have customs duty issues so long as you pay the VAT in the source country (a member of the EC). I've purchased from Teleskop Express (Germany) several times & had no issues - very firendly service, excellent stock & prices which are pretty competitive, especially for larger items where it often seems to be much cheaper to ship from Germany to Northern Ireland than from the British mainland to NI. No, I can't work that one out, either.
  18. 10 x 1 min exposures contains sqrt(10) = approx. 3.1 times as much reasout noise. 1 x 10 min exoosure burns out the detail in bright parts of the image at 1/10 the surface brightness that 10 x 1 min exposures do.
  19. Sorry but when my ears were young enouigh to hear reasonably well I could tell the difference between mid-range excellently specced hifi and high-end stuff with "numbers" that didn't look as good. There's a huge difference between music and the continuous sine waves used to derive performance figures.
  20. Yeah, they're all much of a muchness in so far as you pay much more for a bit better performance. There's none of them perfect but they're all pretty reasonable. Coronado/Meade PST or Lunt LS35 is a great "budget" introduction but the 60mm scopes are serious pieces of kit that should give many years service. Don't buy a second hand solar scope or filter set without trying beforehand or a solid "return for full refund" guarantee. The etalons are very sensitive to mechanical shock, and having a bumped one recontacted is an expensive repair. And the older Coronado scopes may have "rusting" issues.
  21. Hyperion is a real toughie even with 10"+ ... best seen when close to Titan & in elongation, as it was yesterday. But there were also a couple of mag. 12 stars in the area which you would be much more likely to see.
  22. Rubbish!In one of the Goon Shows, an official from the Royal Geographic Society cadges a ride in a rocket (constructed & manned by the Goons) in order to check the flat earth theory. As the rocket is rising, Eccles sees the earth through the window: Eccles: "Hey, I just saw the Earth through the window!" Official: "Did it look round?" Eccles: "Yeah, but I don't think it saw us"
  23. The big difference between camera lenses & scopes is that (with a few exceptions) scopes are designed to be ultra sharp on axis without much care for what goes on away from the centre of the field, whereas camera lenses have to be reasonably good over a wide field. In olden days, "long tom" tele lenses were essentially just doublet or triplet scope objectives. Nowadays we have sophisticated multi-element refractors with field flatteners, more or less equivalent to camera lenses & just as good over a fairly wide field. So the distinction is being lost. However, it still follows that a camera lens does not have to be as sharp on axis as a scope objective does ... the film / sensor just does not have the resolution to cope with the difraction pattern made by a "perfect" objective, unless the working focal ratio is in excess of f/20. For this reason, camera lenses fitted with an eyepiece usually perform quite badly.
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