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JohnSadlerAstro

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About JohnSadlerAstro

  • Rank
    Proto Star

Profile Information

  • Gender
    Male
  • Interests
    Aerospace, Aviation Gaming, RC Aviation, Electro Swing, Technology
  • Location
    Chippenham, Wiltshire
  1. JohnSadlerAstro

    The Astronomer Fashion Awards

    Me and the 90s Gold seeing this thread be like: Generic hoodie with shorts and pink headphones (I can win with these): cold in 12 degree heat. Needs to visit barber. This outfit is entirely impractical for astronomy, but isn't it always the most impractical stuff that wins fashion shows? The annoying this s forgetting how cold I am until its too late. Why is it that every pair of headphones I've ever had broke except those dreadful 6yr old pink ones! <sounds of shattering convex lenses> John
  2. That explains why mirrors went to Parabolic shapes, instead of being corrected at the eyepiece. I'm guessing the only reason why this would be worth it would be in extremely large mirrors, when making it parabolic would cost more than the corrector. How simple are the MPCC 4s optically speaking? They seem to just magnify the centre, but there must be more going on! John
  3. Thank you for starting the thread--its great to learn more about this topic, I'm slightly ashamed I knew so little to be honest! Really helpful and interesting diagrams @Louis D and @pipnina, thank you for sharing! I don't think my 130PDS mirror is 5 degrees off axis, although I did once go for 5 months without noticing the primary had slipped one of its shoes. I thought it a bit odd that I had to collimate at about 10 degrees of straight! John
  4. Surely spherical aberration could be corrected using a lens very similar to glasses? Isn't it roughly equivalent to astigmatism, except that it is predictable and symmetrical across the fov? John
  5. JohnSadlerAstro

    Taking the next step

    Hi, I haven't used any of the scopes you listed; but you could take a look at the PDS range -- I have a 130PDS (f =650mm) and its a beautiful scope for imaging and visual on DSOs, also very sturdy and well-made. The only downside is the collimation. John
  6. Hi, So a spherical mirror is a Spherical section (hollow circle chopped through near its edge), its gradient's gradient (second derivative, f " [x]) doesn't change (I'm pretty sure it stays at 1, someone please correct me if I'm wrong ). Whereas, a parabolic mirror is a parabola section--a cone cut parallel to its centre line. As a general rule of thumb, I think you'll find it's taller at the edges. The parabola focuses rays at the same distance, (no spherical aberration) but "splats" the image when it hits a non-parabolic surface like the secondary, producing coma. I think a hyperbolic will act as something between the two--but usually only spherical and parabolic are used in newts. EDIT: After some research, it appears that a hyperbolic is used for very fast systems, like cats and astrographs. John
  7. Just to throw this in as well--I have heard of hyperbolic mirrors. I assume these would act like a compromise between S and P? John
  8. JohnSadlerAstro

    FIRST Mono RGB combo Image M13

    That will be exciting--all the shots Ive seen comparing the two are processed and captured differently, and most often taken with different kit. Looking forward to seeing the results! John
  9. JohnSadlerAstro

    FIRST Mono RGB combo Image M13

    I can't look! 9 mins for the dumbbell...eventually I will have to sellout and buy a CCD. What are noise levels and sensitivity in long expos like compared to DSLR? I've been told that the CCD is waay better in those areas, but I've never seen a straight-up comparison shot between the two. John
  10. JohnSadlerAstro

    Does This Part Exist

    Hi, Ive become increasingly irritated by my old EQ2's lacking a quick release. Every time I want to put my OpticStar onto it, I have to take off the dovetail bar and bolt the rings directly onto the mount head. Does anyone know if there is an EQ2 mount head -> Standard SW quick release available? Unfortunately I have neither the materials, machinery, or skill to make one! John
  11. JohnSadlerAstro

    Life on other worlds in our solar system.

    That sums up my point far better than I can. John
  12. JohnSadlerAstro

    Life on other worlds in our solar system.

    Why should we assume that the definitions of Living and Non-living apply across the universe in the same way as they do here on Earth? If we didn't recognise "life" as life, surely it by definition wouldn't be life? Our Earth-based categories have no need of being stretched to the universal scale. I would argue that "life" only exists on Earth, and Earth-like planets. "Life" is things we can recognise as life based on our Earth-based observations and definitions. Why should intelligence found on other planets necessarily be "life"? It's a bit of a silly example, but let's say that somewhere people only knew about bananas. Their definition of banana is a long fruit coloured yellow or green with white fruit and an easy to peel skin. When they saw an apple, they say "well that's a special kind of banana", and modify their definition to include all green, red, or yellow fruit. When they see a plum, they modify the definition to include purple fruits too. After a few years, when the people have seen everything in the world, they are confused because while (based on their carefully constructed definition of a "banana") everything is aparently a banana, the definition is so complicated and ridiculous that it's obviously false. This probably doesn't make much sense--I'm not very good at explaining stuff. John
  13. JohnSadlerAstro

    Vulpecula widefield.

    That's a beautiful part of the sky--and an amazing photograph of it. The star colours are really natural-looking, as well, which is something photos with lots of Ha often fall short on. I was out on Thursday night under the Milky Way, it had been a difficult day and sitting against the tripod gazing up at the Cygnus area as the sky got darker and the clusters slowly appeared was the best way to relax! John
  14. JohnSadlerAstro

    Vixen ED103S - Say Hello

    @John Is that SW frac, the gold one, a special edition or something? I've never seen any SW colour other than the old blue and B & W. It looks perfect for a "sellout" setup to keep the clouds away! John
  15. The person designing that must have forgotten their physics. F/2!!! That is just stupid. I wonder if it has a 1:1,000 focuser. John
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