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Peter Drew

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About Peter Drew

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    Main Sequence
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    Astronomy Centre Todmorden U.K.
  1. Very true, but the Littrow can be oiled as three of the surfaces are identical so not such a "bad" scenario as it seems.
  2. I wouldn't worry too much about coatings at this stage, none of the early great astronomers did.
  3. Nice one Charl, you certainly make the best of your opportunities! I was lucky to get a good visual earlier with my big Ha scope, best prom for quite some time.
  4. Size for size and similar focal ratios the Fraunhofer is a better design. It is slightly more achromatic and field coverage is better if AP is a consideration. The Littrow is "easier" to make, needs little specialist equipment for testing and is less sensitive to cell mounting issues. I've used a number of uncoated Littrow objectives and can't recall ghosting issues, modern coatings, if applied should overcome any.
  5. Depends also on what telescope you are using the zoom on, 24mm isn't a low power on a 16" SCT, an individual single wide angle eyepiece is certainly needed.
  6. When I said you could have them I meant FOC. I'm not going to anything with them and they would only get lost or broken in due course.
  7. Excellent review Steve of , as you say, a well thought-out binocular. I think the (justifiable) high price might well limit its sales.
  8. The two suspects for this result are squaring on of the optical train and spacing of the coma corrector. If this was the best the cc could do then I think is belies its description.
  9. If you are seriously considering having a go at making an achromatic doublet I have a pregenerated crown and flint pair for a 5" aperture Littrow design objective you could have. The Littrow design would be a good starter as r1, r2 and r3 curves are identical spheres with r4 being flat. With your mirror making experience it would be worth making a spherical mirror of the correct radius to use as a test plate for r1 and r2 on the crown and then test the flint r3 on the crown.
  10. I'd rather not add it up! I've bought only one brand new telescope, a SW 102mm F5 Startravel as I couldn't wait for a used one to appear to complete a binoscope I was building, all the rest were either purchased secondhand, received by donation or built by myself.
  11. For the 2006 total eclipse in Turkey I used a 10x50 binocular for visual during totality and a miniDV camcorder to record it. Superb results with both.
  12. +1 for the recommendation.
  13. That would be your best bet, I think there is an external securing ring, once removed the secondary unit can be withdrawn. If the securing ring is tight be careful you don't rotate the corrector plate.
  14. That's the point, you don't align on Polaris, just the point in the sky near it, Polaris is just the best guide.