Jump to content

740427863_Terminatorchallenge.jpg.2f4cb93182b2ce715fac5aa75b0503c8.jpg

SimonR

Members
  • Posts

    58
  • Joined

  • Last visited

Everything posted by SimonR

  1. A movie has been made on the space station that tries to show what Yuri Gagarin might have seen on his historic flight around the Earth in 1961. BBC News - Movie recreates Gagarin's spaceflight
  2. I'm not sure what it is about the 'genuine orthos', they have the wide rubber tops that I find hard to use at short focal length. Equally genuine are the classic 'volcano top' orthos that have been made in Japan for about 40 years. They are marketed under various brand names but appear to be made in the same factory, they have the 'Circle T' mark on them. I bought mine direct from Kokusai Kohki in Japan but you can get them in the UK from Lyra Optics and in the US from University Optics. I have a set of them 7mm, 9mm and 12.5mm, I also have a couple of Circle T Erfles in 16mm and 25mm. The 7mm ortho is very usable, I'm not sure that it would be if it wasn't a 'volcano top'. Links: -> Lyra Optic - Eyepieces -> Eyepieces - 1 1/4" Oculars from University Optics -> Kokusai Kohki
  3. Another approach, simple and functional, a £4.99 plastic component box from Maplins. Works perfectly well for regular sized eyepieces. I like Japanese volcano tops:
  4. The amount of eye relief depends on the design, plossls which are very common don't have a lot of it. I find a 6mm plossl very hard to use even with my glasses off. With my glasses on I find I can use a 9mm orthoscopic which has eye relief of 7.2mm, but it is the 'volcano top' design which is easier to use than a 'rubber top' if you wear glasses.
  5. I knew that focus means fireplace in latin, but I didn't realise that lens means lentil. I like that. An achromatic lentil.
  6. If someone really doesn't want to believe in it, they won't. Even if you do have a photo they will claim it's a fake:
  7. I do sometimes wonder if taking up astronomy in the UK is something like taking up skiing in Jamaica, and yet I get the impression that the UK has an unusually large number of amateur astronomers, perhaps it is an eccentricity. We are one of the most urbanised countries in the world, and we are trapped between the Atlantic and the North Sea, for most of us light pollution and clouds are the norm. I think a lot depends on your expectations, if you just want the occasional look when the opportunity is there then it is reasonable to invest in some modest but well made equipment and enjoy the clear nights when they occur. Whenever I start looking at big telescopes, checking star charts for faint objects, when the possible spending begins to climb, I only have to look out of the door and my ambitions are dampened by the weather. I do enjoy my binoculars and now my telescope, astronomy for me is a diversion, it takes me out of myself to somewhere very big, that is its place.
  8. It's a long time since I've read any, but when I did it was Arthur C Clarke and (especially) Stanislaw Lem. I'm not sure if Ray Bradbury counts, but I liked his books too.
  9. I've dropped your scope and EPs into my spreadsheet to see what it looks like. I've assumed a 50 deg field for a Plossl. You seem have it pretty well covered. You can see what a 32mm adds. To put the True Field of View into perspective, the Moon is about 0.5 deg across. A magnification of 23x is very, very low; but that's a 2 deg field of view. EDIT to add - look at the exit pupil figure, it's near the limit for the 32mm.
  10. I think the consensus is that they are OK but not great. If you are on a budget you might look at the GSO ones which cost a little more but offer a lot of quality for the money. Beyond that, the sky's the limit. What eyepieces do you already have? A 32mm could be very useful, it is the longest Plossl you can use on a 1.25" tube.
  11. There's a vagueness in the search engine, it's trying to be helpful. I tried 'erfle' and got 'erf' diesel engines. They are nice but not for my purpose.
  12. Import duties add at least 30%. You can get these in the UK, peak2valley instruments have them and the Istar refractors too: LINK peak2valley instruments
  13. Have you checked out this - Astro Babys HEQ5 Polar Alignment
  14. Computer says 10^9 seconds = 31.7 years. Spring 1979.
  15. I doubt that they are, but they are very good. A long refractor, like F10 or more, will have far less of a chroma problem than a short one. With good eyepieces I don't really notice the chroma on my one unless I am looking for it.
  16. Not quite sure what you mean. The 12mm will retain it's original apparent field of view, which might or might not be the same as a 6mm. The true field of view will definitely be different.
  17. I've bought eyepieces from Japan. Import duty and charges etc. added about 30%. If you can get what you need from the UK (or the EU) you might as well because it adds up to about the same. I ordered the ones I did because they are not available anywhere else. They can take a while to arrive, I tracked the order - it took 24hrs to go from Osaka to Tokyo to the UK. Then 3 days at Coventry clearing customs and another 2 days at the Parcelforce depot before I got a note asking me to pay the duty.
  18. I've been using 7x50s for years. 10x50s are about the same size. I think anything bigger is going to be a real handful, they will be tiring to hold after a while, they will need a mount of some kind. Even 7x50s need to be held against something. I suppose it depends on whether you are going to use them instead of a telescope, in which case I would go big, or as an extra, for travel and as a quick 'grab and look'. The reason I use 7x50s, which are low magnification, is that I am also into sailing and they are the standard in the marine world because they are easier to keep steady. They still jiggle about a bit, but less than most. Also, in theory 7x50s have an exit pupil that is oversize and 10x50s are more sensible, but; imagine being on the deck of a rolling boat, the oversize exit pupil makes eye placement less critical. Simon
  19. I'm in south Suffolk, not so far away. Last night was great, I was up until 4am. I found M81/M82 at last, and I got to try out my new orthoscopics on Saturn. Tonight looks like it is going to be even better, just need another pint of coffee...
  20. Hi, and welcome from England. I was in Arizona two years ago on vacation, what skies!
  21. For the solar system, I really enjoyed Planets: A Very Short Introduction by David Rothery. (On Amazon.)
  22. Completely agree with the above comments, magnification is mostly limited by the atmosphere, and magnification is not, generally, what it's about. I was trying to answer the original question directly - "What happens when I exceed that [theoretical maximum] magnification? ... I'm just curious to what happens..."
  23. There are several dimensions to this, there is a theoretical limit to the resolution of a telescope, there is a limit imposed by the atmosphere - the 'seeing', and there are others. An important limit is the exit pupil. Imagine the cylinder of light entering the front end of your telescope, the lens or mirror system reduces this to a much smaller cylinder of light emerging at the eyepiece. The diameter of the cylinder of light at the eyepiece is called the exit pupil. It is easy to calculate the size of the exit pupil - it is the diameter of the objective (the aperture) divided by the magnification you are using. So, if you have a 100mm telescope and are using a magnification of 50x, the exit pupil will be 2mm across. At a magnification of 100x it will be 1mm across. High magnifications make the exit pupil small. The problem is that when the exit pupil is smaller that about 0.5mm it is getting similar in size to the imperfections we all have in our eyes and you will begin to see all sorts of distortions (diffraction, floaters, etc). This leads to a rule of thumb that the maximum useful magnification is equal to twice the aperture in mm (or 50X per inch). Above this you exceed the limits of your eyesight. Here's a link to a slightly technical explanation of the limits: LINK Telescope Function
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.