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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

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  1. B

    Star Testing

    Yes. But the extender might not be optically perfect, but should be quite good.. Regards, B.
  2. B

    Star Testing

    I have had good star tests with not very good optics. For me, I am used to astro telescopes. I put a high power eyepiece without an image erector and if Saturn, Jupiter or Mars are available at a reasonable elevation, I use these. Say 50 times per inch of aperture. I also star test them. If...
  3. B

    Star Testing

    Thanks John for the correction. I have been jabbed in both arms for Covid and flu reasons and am a bit groggy. At least I feel boosted. Whether they will manage a million Covid jabs a day I don't know. For £20 the Timex lasts an amazing amount of time considering how much I use the light...
  4. B

    Star Testing

    Hi Randy, It depends on the focal ratio, focal length and aperture. My 100mm f/12 Pentax astro refractor, which was a Pentax demonstrator could easily be used on planets at 300x and tested well at 400x with no image breakdown. This was a doublet, but I don't know if there was any hand...
  5. B

    Star Testing

    Hi Randy, No. Roland Christen is I think referring to Apo triplet high quality astro refractors. Here he says that the star testing fraternity have got it wrong. He can reduce the quality of his scopes to satisfy their mistaken opinions regarding out of focus star images. But I doubt that he...
  6. B

    Star Testing

    As to under or over correction. In astro scopes temperatures dropping in the evening mean that some makers deliberately correct for temperature dropping rather than steady temperatures. There is a well known case in New Zealand where the professional observatory scope of about 24 inch...
  7. B

    Star Testing

    The lens designer or spotting scope designer has to make a choice as to which aberrations he or she wishes to correct. With fast systems these choices are more selective. Even before tolerances are considered it is likely that not all aberrations can be corrected. That is why I prefer long...
  8. B

    Star Testing

    Hi Joker, I am not making fun of you at all. I am just pointing out the difficulty of finding a real cherry of any type of optic even from the best makers. There are tolerances for everything. wedge, centration, figure etc. There is no perfection. I have seen and handled $1million lenses...
  9. B

    Star Testing

    Hi Joker, You need to do what Stanley Kubrick did. :) Instead of renting lenses like everyone else, he bought ten of the finest lenses, tested them all and used the best of the ten for the movie with the second best as back up. Unfortunately for Barry Lyndon he only had three of the Zeiss...
  10. B

    Star Testing

    The star test seems O.K., but affected by poor Seeing and temperature effects. One cannot reject a scope because of imperfect weather conditions. The proof of the pudding is in the eating. If a scope performs well in actual use at all available magnifications, then it is good enough and fit...
  11. B

    Star Testing

    The best Seeing conditions here are at 3 a.m. Almost as good sometimes at 2 a.m. A star for testing should be high and say magnitude 2 to Mag 0. Planets should be high. Unfortunately not so in northern hemisphere currently. A spotting scope should be out for 20 to 30 minutes but not so long...
  12. B

    Star Testing

    Hi Joker, It might be the Seeing and temperature variations. Was the temperature day and night similar? My friends use the jet stream to decide whether to observe or not. I cannot remember, but anything over 50mph is poor and also the direction. Maybe try the scope on Jupiter at the highest...
  13. B

    Star Testing

    No, I am not saying that. A poor star test will affect the quality of the in focus view. But at the lower magnifications used by bird watchers, the effect may not significantly affect the ability to identify birds. Also people with very fine eyesight will be more affected by a poor scope than...
  14. B

    Star Testing

    True. Spotting scopes seem to be f5.5 or f/6. It also depends on the aperture. It seems that the Kowa 99 and Swarovski 115 may have very fast front elements with extra magnification from the elements behind to make them very compact. Optically speaking I would think it difficult to make them...
  15. B

    Star Testing

    This is high end stuff by two world class opticians. For a beginner to star testing with the average spotting scope the simple instructions should be valid. Personally the test of high end optics comes with planetary observations. But it takes years of experience. The planets are in focus...
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