Jump to content

 

1825338873_SNRPN2021banner.jpg.68bf12c7791f26559c66cf7bce79fe3d.jpg

 

Merlin

Members
  • Posts

    680
  • Joined

  • Last visited

Everything posted by Merlin

  1. The Coathanger’s been mentioned as an open cluster, but isn’t it classified as an asterism? There is an ancient and, apparently, understudied open cluster at one end of the Coathanger.
  2. I have a Skymax 90mm ‘scope and get superbly sharp views of the Moon with the WO binoviewer. Jupiter and Saturn look good too for the aperture.
  3. Perfectionists might wince at this, but I’ve made my 20cm Newtonian a closed tube ‘scope. I went to Asda’s to see if I could find a clock with a glass front big enough to play the part of an optical window. Having found a suitable clock for just £6, I removed the very thin glass front and its bright aluminium collar and found that they fitted snuggly over the front of the ‘scope. The rear end of the tube was closed off with a piece of foam. Now to try it out.. . The Moon was the first target. The new arrangement yielded sharp images at quite high magnifications. Then, I tried the stars in the Pleiades. Again, the images were sharp and, surprisingly, there was no sign of astigmatism. Finally, I made a dew shield from a piece of rolled camping mat. I haven’t tried the ‘scope yet with the highest magnification of 400x as the primary needs a recoat, but it looks promising. It’s been suggested that front aperture glass solar filters with their coatings removed would make good optical windows. A 20cm solar filter can be bought for about £100, but the problem is knowing how to remove the protective coating.
  4. Maybe the flat itself has stress lines in it due to poor annealing.
  5. I use a 7-21 zoom on the PST. It makes for a compact arrangement.
  6. A small spottingscope, ranging from 65 to 80mm aperture, is recommended by some for lightweight portability.
  7. I have a mongrel solar ‘scope. A PST double-stacked with a Lunt LS50f etalon. It works, but it’s darker of course.
  8. The thing about wobble is that the tripod can be more responsible for it than the mounting. Put the mounting on a sturdier tripod or other solid base and we can sometimes witness a transformation.
  9. It used to be said that the way to remove dew from an objective is to put a warm handkerchief inside the dewshield and cap it for a few minutes.
  10. I bought the Lidl refractor Year’s ago. The ‘scope’s okay on low to medium powers, but shows some astigmatism on higher powers. I now use the ‘scope as a Stage 1 mod for solar viewing. For the money, the ‘scope wasn’t a bad deal. I quite like the EQ2 mounting.
  11. Vibration can be a problem in many ways. When my daughter was a child, she was in the habit, as many children are, of jumping from last few steps in the staircase onto the floor. Alas, this habit ruined several LPs by making the stylus on the record player in the lounge jump across the vinyl, leaving pits and scratches on its surface.
  12. What’s the aperture of your ‘scope Dave?
  13. Many of the Newtonians we see today, including my own, have main tubes that are too short at the top, allowing a considerable amount of stray light to enter the tube and reduce contrast. If we look through the drawtube and can see out through the top of the main tube ( ignoring the flat ), we need an extension. I made a foot-long extension for the 8-inched by rolling some camping mat material into a tube and lining it with Matt black art card. The main tube extension fits like a glove and also acts as a dew shield for the flat. M anufacturers probably make the main tubes too short to make their ‘scopes look more compact, but this is at the expense of contrast and also makes the flat more prone to dewing.
  14. I was lucky to obtain a superb ex- military mirror for my homemade mirror-mount. It cost just £3 on a flea market. It’s so good that I bought a second one the following week. The coatings are perfect. Originally, the mirrors cost over two hundred of pounds each. They were well boxed and could be war surplus, which would make them very pricey on today’s money.
  15. It’s been said that a well made, correctly adjusted, Newtonian reflector is superior to any folded-beam instrument.
  16. My son lives on Jersey. I’ve never been, but he says that starry nights are superb there. There’s very little light pollution. I remember in the 1950s when it was possible to see Uranus with the unaided eye from the centre of town. Alas, those were the days for stargazing... .
  17. Put your secondary mirror on the end of a thin rod, the existing one must be causing a massive deffraction effect.
  18. Some years ago, Jim Hysom at AE repolished a four-inch/f.12 Fraunhofer objective for me. He did an excellent job.
  19. Bear in mind that if, at some point, you do a PST mod. it’s absolutely essential to have a D-ERF ( Energy Rejection Filter ) over the front of the donor ‘scope. Please don’t attempt a PST mod until you have all of the information you need. I modded a 70mm refractor and it gives good results.
  20. You won’t go wrong with Opticron. I have a pair of 8X40’s, very good.
  21. We can hold X20 binoculars quite steadily if we mount them on a triangular frame with handgrips on the bottom. I made a frame from aluminium tubing and it works well with the 25X70 bins.
  22. I once witnessed a solar flare. It became intense white then faded, all in a few minutes.
  23. The minimum magnification that can usefully be used on a ‘scope is about four times the aperture in inches. That’s X20 with your five-incher
  24. It’s better if contributors to the thread say what kind of ‘scope they are using. Only one contributor has done this. Thanks. Stating the instruments used assists beginners and upgraders to know what to expect from a particular solar ‘scope.
×
×
  • 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.