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umadog

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Everything posted by umadog

  1. I reckon the cure is in two steps: 1) Buy the biggest telescope you can just about physically handle. You won't want to go bigger after that. 2) Go somewhere really, really, dark with whatever aperture telescope. After that you have dark-skies fever and you'll care less about the instrument. You can likely skip straight to step 2.
  2. Hmm.. Good thought. I need to organise myself before I get out, though. Live in an apartment and don't own a car (yet?). So not off to the best of starts. Van rental seems cheapish, though, if I want to get the big scope out to somewhere dark. But with the days getting longer there isn't much point now. It's 9pm right now and still not dark. Maybe I will try setting up behind the apartment building and looking at Jupiter.
  3. I don't have any. I've borrowed some at star parties and the views are nice but they don't improve my experience of the hobby so I never bought one.
  4. Personally, I would buy a suitable collimation device. I've found it pretty hard to do using a star unless the scope is small enough that you can look through the eyepiece and tweak the primary mirror at the same time. Also, IIRC, you can only do the more critical primary alignment with a star test. With a collimation tool (or tools) you can sort out the alignment during the day and leisure.
  5. The area around Hitchin is possible in the first instance. I've tried just south of Oxford in the past too. But I'm lacking a specific location or a procedure for finding specific locations. Dengue looks good longer term.
  6. Hello, I have unfortunately moved to North London, which is even more light polluted than ever. A colleague recently asked me if we could go observing and I realised I have little idea where to go. I can borrow a car and I'm looking for somewhere within, say, 60 to 90 minutes of north London. Ideally somewhere without doggers, people pretending to look at owls, and all the other rubbish that takes place in rural car parks after dark. I'd probably go with a 10" but might do 18" if the site is right and I'm motivated enough to hire a van. Suggestions?
  7. 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:
  8. 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.
  9. 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!
  10. 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.
  11. Given the broad nature of your question, I would suggest you go to your local club and start from there.
  12. 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.
  13. 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.
  14. 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.
  15. 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.
  16. 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.
  17. 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.
  18. 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.
  19. 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.
  20. Nobody said you'd see it by eye. It was photographed during the day. Different ballgame, that.
  21. 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}
  22. Dave's post answers this nicely. The key thing is that each location in the image is created by light coming from the entire mirror. The location that really matters in terms of seeing bad stuff in your image (like dust spots) is the focal plane. The optical element nearest the focal plane will be a lens element in the eyepiece. Which element it is will depend on the eyepiece design, but it's likely one of the innermost ones. Get dust on there and you will see it. The optical term for this is a "conjugate plane". The primary mirror focal point is conjugate with your retina. These planes are used to good effect in microscopy to provide uniform and dimmable illumination. See this: http://en.wikipedia.org/wiki/K%C3%B6hler_illumination I reckon the same sort of thing is probably done with an SLR iris, but I'm not sure. If you want a graphic depiction of how little effect damaging the objective has, you should see this: http://kurtmunger.com/dirty_lens_articleid35.html Amazing, huh?
  23. Qualia, where is the region you call the Black Triangle? I really should get out there some time.
  24. I know the traditional response to this question is not to clean the mirror unless *absolutely* necessary, but I'm inclined to disagree with this blanket "rule". There was a study a while back by an observatory and they showed that regular cleaning prolonged coating lifetime. I can't find the link now, though. So a correct cleaning procedure does not damage the coatings. Even simply hosing down the mirror with DI water will clean it to some degree and this is 100% safe on the coatings. On the other hand, if you leave it dirty then stuff that's on the mirror gets cemented to it by dew/drying cycles, etc. This stuff can eat away at coatings and promotes more dew formation as droplets tend to nucleate on it. The longer you leave it, the harder it is to clean off. The concern with mirror cleaning is that it opens up the possibility of dropping it, etc. If you have a good protocol for accessing the mirror and you're confident, then I see no reason not clean it three times a year. If you aren't happy doing this, then just don't clean it at all and have it re-coated more often. I know that a dirty mirror still functions remarkably well, but that doesn't mean the views haven't been impaired due to increased scatter and decreased reflectance. If the mirror is getting dirty slowly then you won't notice the gradual reduction in the image quality. So looking though a dirty scope and seeing perfectly acceptable images doesn't tell you the whole story.
  25. I have the Sumerian 10" travel scope. The truss is remarkably rigid. The flexure all comes from the top ring but, in my experience, it's not really that severe. The Canopus have a proper OTA, so that issue should be gone. I've got excellent planetary views out of my 10". The only thing I don't like is the lack of a proper mirror cell. The mirror sits on the nylon screws and collimation is a little annoying. It's still perfectly possible, just not as nice as a regular cell. The other issue is that it's harder to mount stuff on the scope and it's too light for a paracorr. Other than that, it's a great instrument.
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