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Peter Drew

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Peter Drew last won the day on January 14

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About Peter Drew

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    Astronomy Centre Todmorden U.K.
  1. I have the similar Vixen model. The first thing I noticed was that, due to the Galilean optical design, the apparent field of view was smaller than that of traditional binoculars. However, it's the actual field of view that sets them apart, whole constellations at a time!. There is definitely around about 1.5 mag gain over naked eye, faint naked eye objects become obvious under most conditions. They are quite front heavy, you may struggle to keep them in place hands free with just a strap, I ended up making a bracket which I fitted to the peak of a hard hat and this needed a counterweight to the rear of the hat for balance.
  2. @Rich1980. The West Yorkshire Astro Society are an active group that meet at the Rosse Observatory at Pontefract.
  3. I also have a TAL-1 telescope with a spherical mirror, the performance is outstanding for the aperture.
  4. It is quite easy to mix up the results of Ronchi testing without knowing how it was performed. If testing a mirror whilst working it, the usual procedure, the Ronchi screen will be at the radius of curvature and a parabolic mirror will exhibit convex lines. If a parabolic mirror is tested on a star at infinity, the Ronchi screen will produce straight lines if all is well. I think this is also highlighted in the CN discussion.
  5. These don't look like parabolic images gained from basic Ronchi or Foucalt tests. To me they look like null tests where the parabola gives a simulated spherical image by introducing corrective optics, the Dall null test. I used a similar setup on my optical bench when I was a professional telescope maker.
  6. A similar scenario with car insurance. I have "fully comp" like most of us these days so if my car is stolen and not recovered the insurers pay out. Not so!, in the small print it states that if the car isn't fitted with a tracker, you're not covered for theft. This is a household name insurer.
  7. A small aperture mirror at F10 spherical will be equivalent to a 1/4 wave parabolic one. I don't think a Ronchi test would be sensitive enough to show much difference. A Foucalt test would be preferable as a sphere completely nulls out when it's a good one.
  8. As Peter has said, the difference between a spherical mirror and a parabolic one at those specs is minimal. In fact you are more likely to get a good sphere than a good parabola on an entry level telescope.
  9. We'll all probably leave at the same time when it hits. Problem sorted.
  10. Good seeing today. Two excellent proms on opposite sides of the disc, faint but very detailed. Several other minor projections.
  11. Beautifully clear still here for a change. First light through the Dall-Kirkham at last. Have to say, very impressive so far despite the awful condition of the mirror coatings. The optical set is a David Hinds "A" grade, I bought them, well used, several years ago and only recently built them into a usable telescope. Once fully sorted and re-aluminised I'm hoping it will be my "Mars" telescope next year.
  12. Generally, if the target star is too bright, the glare swamps the finer quality details under test. Usually, if the out of focus star image looks round either side of focus, a small dot without spikes and no smearing to a side when at focus, you're off to a good start.
  13. Any reasonably long focal length 50mm/60mm achromatic refractor should be adequate. A Huygenian eyepiece, having no cemented optical components, would be preferred to avoid heat damage. There should be no significant fire risk, the heat will be concentrated at the focus of the eyepiece rather than the focused projected image. An umbrella might well be the best "umbrella" to protect kit against rain.
  14. Hoping to see the Moon tonight for first light through my 300mm F20 Dall-Kirkham.
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