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About umadog

  • Rank
    Brown Dwarf
  • Birthday 20/01/1979

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  • Interests
    visual observing, solar observing, building microscopes, seeing stuff with microscopes, dangerously powerful IR lasers, neuroscience, insects, programming things with stuff, failing to learn Greek properly, American IPA, chickens,
  • Location
    Basel, Switzerland
  1. Night Vision - Red Light Myth

    Stub Mandrel, you're right. There's nothing particularly magic about red light but it's critical that the light is dim. However, red is still the best choice, as you can see by looking at the photopigment absorption curves: They're pretty overlapping, but the "red" cones (properly called long-wave sensitive cones) are furthest from the rods (shown in black). So with a very narrow 600 nm light source, you're stimulating your red cones a good deal but the rods hardly at all. Thus, you can read and see colour (red) but not be affecting the rods too badly. Choosing the right LED is important. LEDs don't emit at just one wavelength, but have a range. Some are broader than others:
  2. I have not used it, but I'm wondering if you can tell us a little more about what you want to do with it? Maybe there are better alternatives out there for your purposes.
  3. TBH, I'd say it'll be just fine for planetary observing. The central obstruction on all visual Newtonians is so small you won't notice the contrast hit. At higher powers (which you'll be at for planets) you're using the central portion of the field of view. You care about that, because the outer portions will have noticable coma at f/5. An 8" scope is more than a starter scope: you can keep if for years and not exhaust what it will show you. Go for it!
  4. Other than making sure they can look through it, I'd more or less forget the children in this equation. The adult would have to do, or at the very least supervise, everything. So the adult should choose what works best for them. At 100 quid the choices would look the same with or without the kids being considered.
  5. horse head

    Given the broad nature of your question, I would suggest you go to your local club and start from there.
  6. A penny viewed from what distance? The moon is half a degree across (31 arc minutes). Jupiter is at least 30 arc seconds (when it's furthest from us). So if you magnify Jupiter 60x it will appear at least the same size as the full moon does to the naked eye. It'll be twice the size at 120x and so forth. It may feel smaller because the apparent size of an object also depends on distance cues and you don't have any of those through a telescope. Remember that the moon and constellations appear to be much larger when near the horizon, when in fact their size doesn't change.
  7. A filter won't help in any significant way. Personally, I don't even use a moon filter. Dew will only impact viewing if your mirror is coated in it. Otherwise it makes no difference. You not being dark adapted also makes no difference for Jupiter, which is pretty bright as things go. Light pollution makes no difference for Jupiter either. In fact, some observers believe that remaining light adapted it better for viewing Jupiter. Unless you have a bright light shining directly at you and obviously illuminating everything (e.g. being right under a streetlight), I wouldn't worry. The higher Jupiter is in the sky, the better. Don't bother until it's above about 25 degrees from the horizon. It should look bright and whitish with two coffee-coloured bands. The small brown round thing you describe isn't right (unless, possibly, it was very low to the horizon). You can't judge collimation by your ability to look at the moon. I suggest you read through one of the collimation guides on line and spend time learning and understanding the steps. Once you do this (and learn how to star test) then you'll know if it's collimated right. As an aside, if it's not collimated right you will likely lose contrast and may also lose brightness if things are really off. I would expect you would see a nice view at 100x to 150x on most nights. Unless the seeing is horrific, you should be seeing the bands clearly at those powers. If the conditions are good you could expect to hit maybe 250x. But it should look obviously like Jupiter even at 50x. Heck, I can see the planet and moons with binoculars. If you use too much power on a night that can't support it then the image will be worse. You have the gear right now to get a "wow" view of Jupiter. You don't need to spend money on more gear for now, just figure out what's not working. I wouldn't contemplate AP until you have a really good working understanding of visual observing and understand the gear better.
  8. I doubt you'll have contrast problems due to the telescope speed. Your central obstruction is probably under 25%, so it's not especially large in first place and so more or less not noticeable under any circumstances. Remember that cats have COs in the region of 40%. In addition, to see any contrast loss you need to be operating at near the magnification limit of the instrument. i.e. in your case in excess of 400x and probably closer to 600x. In the UK you are unlikely to reach those powers due to seeing. If you had a 6" f/5, things might be different but with a 12" f/5 it's no bid deal.
  9. This is definitely true. I too see more detail with tracking. The seeing fluctuates all the time and so you have a greater chance of capturing the rare sharper moments if you can just sit and stare.
  10. Ah... I see. I think you're under-selling the 8" as a planetary instrument in that case. They can be absolutely excellent if, in common with other designs, the optics are good, they are cooled down, and they are collimated. This is all that really matters. I know we spend a lot of time here debating optical designs and what is better for what object, but in reality the aperture, the quality of the optics, and how they are set up likely makes more difference than the design in most cases. Nice short focal length eyepieces are now available, so there's no compelling need for the long focal length of a cat. In addition, you're getting a large CO with a cat. Other than the diffraction spikes, the planetary surface views through a Newtonian should be as contrasty as a refractor of the same aperture. COs below 20% have no noticeable effect on contrast and this becomes even less important at larger apertures when the Airy disk is already much smaller than seeing can support.
  11. Why do you say that and what instrument would be better? I have found an 8" to be capable of excellent planetary views. A bit dim at higher powers, but still excellent. When the seeing is good, then even more aperture definitely helps.
  12. I think of it differently. All scopes suffer equally from light pollution. Light pollution just decreases contrast between the DSO and the sky background. This isn't worse at larger apertures, it's a constant. So if an object is visible, then under LP skies the larger scope still shows more. However, LP washes out the fainter stuff first and larger scopes are able to pick up fainter stuff than smaller scopes. Consequently, larger scopes have more unused potential in LP skies. In other words, the difference between an 8" and 12" scope would be more prominent if you're viewing somewhere dark than if you're viewing in suburbia.
  13. Observing stars during the day ?

    I too would be curious to see independent verification of the Ring image. What I find surprising about that image is the hint of colour. I would expect you'd need some pretty heavy averaging and low noise gear to get a daytime shot of the RIng during the day. This is only going to be harder if you start doing the imaging in colour. The lack of any stars in the image I find less surprising, since there are no bright ones in the immediate vicinity.
  14. Observing stars during the day ?

    Nobody said you'd see it by eye. It was photographed during the day. Different ballgame, that.
  15. Observing stars during the day ?

    I'm sure you can see those stars during the daytime. I have friends who go daytime planet watching as a fun lunchtime pursuit. Venus, Jupiter, and Saturn are their targets. Here's an image of M57 in daytime: http://www.astronomy.com/sitefiles/resources/image.aspx?item={695A71D2-A1ED-4831-820A-18212C059E5F}