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brianb

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Everything posted by brianb

  1. When projecting the Sun, you really need as much light through as you can get, a filter isn't going to help (especially the Baader Solar Continuum which is pretty dark). As Merlin says, beware of damaging eyepieces by heat build up - modern eyepieces which have cemented glass elements can be ruined if the cement melts, which doesn't take a lot of heat. It's much safer for your equipment to use a special filter designed for solar observation, mounted over the front end of the scope - Baader solar film is the best stuff there is, and it's perfectly safe for your eyes too, if it's used according to the instructions.
  2. Very happy owner of a CPC1100 here (same mount) but again it's not a deep sky imaging scope ... the same tube on a Paramount ME would work well. The main issue is the same as all commercial SCTs, the (single speed) focus mechanism is a bit coarse - the Feathertouch modification which gives the standard focus mechanism a 10:1 reduction control is good, or you can hang an auxiliary focuser on the back end of the thing. Otherwise - you need a dew shield and a heater tape for the corrector plate end of the tube ... again this is normal with SCTs in an Atlantic climate!
  3. Ash or hickory are better for damping out vibrations.
  4. There is a real issue with making supermassive stars - the radiation pressure from the forming star tends to blow away the outer layers of the material which is still infalling - in the early universe the infalling material would have been quite transparent optically (until heated to ~7000 K) allowing massive stars to form more easily than they do now that the material contains significant amounts of dust grains etc. but nevertheless there is no known means whereby a star exceeding a mass of ~200 solar masses can form, except by very rare events where protostars collide with each other & merge. Stars in the 100 solar mass range which go supernova will produce a black hole with a relatively small mass (a few solar masses) or even just a neutron star core as a remnant. OTOH there are mechanisms whereby black holes with essentially unlimited masses can be formed in the very early universe, just a very small fraction of a second after the big bang (before gravitation seperated out from the other forces). One difficulty with the theory is the lack of permeation of the universe with lightweight (planet mass) black holes ... we don't know everything yet!
  5. Yeah, the moon is just about the only thing that the beginner really needs to use a filter on, and only then to protect night vision. (Apart from the Sun which requires specialist devices). When you have built up a couple of years observing experience, you will learn how to predict which filters will make certain features a bit easier to see. They do not make a huge amount of difference & are certainly not a "magic bullet" which will transform a rubbish scope into a great one, avoid the need for proper cooling or collimation or do much to work around the common issue of atmospheric turbulence ("bad seeing"). Orange or pale red usually helps a bit on Mars. It's worth trying a light green on Jupiter, and a light yellow on Saturn (but only if you have lots of aperture). When conditions are abnormally good, a violet filter may show cloud shadings on Venus.
  6. Yes. The lens appears to have a bit of astigmatism, this is sometimes a result of the optics being "pinched" by the retaining rings being overtightened. Does this mirror lens have thread-in filters in the end that attaches to the camera? Try removing the "plain glass" filter that is probably fitted there, it might be causing the astigmatism & you don't need it for astro work (removing it will change the focus point slightly making the scales inaccurate but that doesn't matter)
  7. Indeed. A really deep red - like the Wratten #29 - passes only very long wavelength light which doesn't have the energy to unlink rhodopsin, the sensing mechanism used by the rods which are responsible for dark adapted vision, but most red filters do. I actually use a white LED torch with a Baader 685nm "infra red" filter over the LED, this gives a very dim deep red light which is ideal for reading charts etc. when observing visually. Eyes do vary, as do observing conditions - you just aren't ever going to get properly dark adapted when there's any more than a thin crescent moon in the sky - but when conditions are ideal, dark adaptation actually continues into the second hour - as measured by what you can see & how easily you can see it. Looking at a bright object, even a planet or a bright star, can undo all the good work. A "pirate" eye patch to protect the observing eye is also a Good Idea .
  8. Sorry but using a focal reducer to get a wider field of view is a chimera ... the field is ultimately limited by the size of the secondary mirror & the baffle tube. With a CPC1100, the best field of view is obtained by: 1. Removing the visual back and the large sct adapter 2. Obtaining a 2" push-in visual back which fits the large SCT (3.25") thread directly 3. Using a quality 2" push-fitting diagonal - if needed, actually you get more FoV by omitting the diagonal if you can cope with the eyepiece position 4. Using a wide angle eyepiece of focal length around 40mm. A 60 to 70 deg AFOV is as much as is needed, any more than that will suffer from vignetting. An eyepiece longer than 40mm is likely to cause issues with shadowing due to the central obstruction, but you may be able to "get away with" 50mm if you have dark skies and young eyes ... in which case a standard (50 deg AFOV) Plossl will fully exploit the maximum field available. Focal reducers inevitably reduce contrast and cannot increase the angular size of the illuminated field of view, in fact the usually reduce it to some extent. They're very valuable for imaging with cameras with smaller chips but not for visual work.
  9. If the focuser is good & rigid mechanically, no. If the focuser is a bit "sloppy" it's better used with less extension which might mean buying an extension tube. But this may be the price that you have to pay if you need to bring the focus out far enough to get to primary focus with a DSLR.
  10. Look here. BTW the "moon buggy" that James May drove wasn't. The real moon buggy would have collapsed if anyone sat on it in Earth's strong gravity field - it was built down to a very strict weight limit & strong enough to work in 1/6 gravity.
  11. Moving the mirror 30mm further forward makes the light vone 30/6.3 = (a bit less than) 5mm broader at the point where it intercepts the secondary. Therefore either the secondary needs to be enlarged by 5mm, or the diameter of the fully illuminated field will be reduced by 5mm. A marginally too small secondary is much more of an issue than a marginally too large one, as the effective aperture of the scope will be reduced. There are also potential issues with vignetting if the scope is to be used for visual or CCD photometry.
  12. It's a sun pillar - caused by ice cloud. Nice illustration!
  13. Yes, for individual images, but you would have to refocus when changing filters & the image scale might be slightly different as a consequence. No - you can't add detail which has been lost over part of the image because it's out of focus (which is what field flatness means). If you're using a small sensor, you maybe get away without a field flattener. With a large sensor (certainly for the APS-C size commonly used in DSLRs) you will certainly need a field flattener with either a doublet or triplet refractor of normal focal length.
  14. Anything over 200x is rare, I've used x311 twice in 2 years with my CPC1100.
  15. It's not a suggestion, it's a fact .. the shift is about 10 cm, the pole is continuously shifting mostly due to seasonally varying distribution of land ice but jumps of a few cm are commonly associated with large earthquakes ... there was a similar shift at the time of the 2004 Boxing Day earthquake/tsunami event, and a smaller one last year associated with the Chilean earthquake. Nothing of significance.
  16. Well, in my opinion the Celestron Ultima SV 2x - which is a 3 element triplet - is far superior to the ordinary 2x barlow bearing the Televue trademark. The TV Powermate is definitely superior to the Ultima - especially for imaging because of the reliable magnification factor, which is hardly affected by the back focus distance - but it is a lot more expensive.
  17. Goto is handy for those of us with a regular observing programme with many targets but is by no means a substitute for the basic ability to compare the object visible on the computer screen or in the eyepiece with the chart or to find the object's field by following a chain of stars from a clearly identifiable object. It's a convenience not a necessity ... and IMO ranks a long way below a motor drive (to keep the object in the field) which is in iteslf a lot less important than a mount solid enough to support the scope firmly, with minimal vibration from wind etc. and very fast damping out of any vibration which does occur.
  18. Umm. As I understand the Chernobyl event, the core was unstable & went from 20% of its rated output to 500 times its rated output in less than 3 seconds - before the building was blown apart by expanding gas resulting from the rapidly increasing temperature. I think that western power company reactors were designed in such a way that an event like that is exceedingly unlikely - unlike the Russian design which was a scaled-up version of the British design involved in the 1957 Windscale event - which was designed primarily to produce plutonium for weapons rather than electrical power. But highly enriched uranium can achieve criticality and indeed must do so (in a controlled manner) for a fission reactor to operate. There's no danger of a nuclear explosion so long as the control rods are fully inserted and that the fuel remains in its rods. If the cooling fails, the fuel can heat up enough to deform the rods & I'm afraid the safety designed in is forfeit.
  19. I do hope that's more than wishful thinking ... I'm afraid that the Japanese nuclear industry has a long history of playing down incidents (though this is clearly more serious than anything they've had before) & the Japanese Govt has a clear interest in playing down the danger because there's practically nothing they can do about it - transport in the area is severely disrupted & they probably wouldn't be able to do a 50 km evacuation even if it was indicated.
  20. It's also wishful thinking ... Penrose is a gifted mathematician & I'd expect to be able to see the predicting model ... but it doesn't seem to exist. M-branes colliding in a (possibly) steady state superuniverse is a better solution to a continuous cycle of big bangs, but it doesn't alter the eventual fate of ours.
  21. Your system is aperture limited by the front filter. You will need to extend the focal length to f/20 - f/25 to enable the camera to resolve all the detail available; a good 3x barlow or tele-extender will allow you to do this. The scope will be fine; to resolve significantly more detail you will need to buy a bigger etalon & this will be very expensive.
  22. If the plates were in isostatic balance before and after, but the denser plate moved lower, conservation of angular momentum would cause an increase in spin speed. We're not talking much here, a change in the day length of a few microseconds .... if you have a very good clock and an accurate transit instrument, you might be able to see the difference after a few weeks. But it's likely that other earth movements will have happened before then to even things out. Large earthquakes happen when movement "freezes" then releases suddenly - in this case, a movement of 90 mm per year has accumulated over many decades & then jumped several metres.
  23. Well, battery life is meaningless unless the temperature is specified ... batteries will go dead very quicky at low temperatures & miraculously recover if they're warmed up. Normal alkaline batteries have an almost zero life at -20C.
  24. but unfortunately has a nasty habit of taking over the whole computer ...
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