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Don Pensack

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About Don Pensack

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    Proto Star

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    Audio, films, traveling, and astronomy of course.
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    Los Angeles

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  1. I don't recommend Hyperions below f/6, and I don't recommend the 31mm and 36mm Hyperions below f/8 Sure, they can be used in faster scopes, but they will have a lot of outer field astigmatism. It's like the Morpheus, which I don't recommend below f/4. In my f/5.75, the 14mm Morpheus is near-perfect. In my friend's f/3.45, it was not good at all.
  2. The Delites have a different lower cap in black that fits the barrel very tightly. Too tight, in my opinion. There is an answer I could have used, in retrospect--simply using some light sandpaper on the interior surface of the caps--it would have taken me only seconds per eyepiece--but I didn't thin of it at the time.
  3. I used copper tape, which also works great--it's thin enough you need a couple wraps but it serves the same function and makes removal and installation a lot easier.
  4. Painted metal? The outer surfaces are: --chrome plated lower barrel --black anodized upper barrel If you are referring to the iris in the sliding eyeguard, the upper surface is black-anodized aluminum. If the eyeguard is used raised at all, even one notch, it acts like a dew shield for the upper lens, not to mention a light trap to reduce peripheral light scatter. I own all 9 focal lengths and the eyeguards lock tightly in place, so "doesn't lock in place" just isn't true. You just not be tightening them sufficiently. I do note you cannot lock them using onl
  5. I agree totally, but the problem isn't the aluminum collet, it's the lower eyepiece cap. They're made far too tight and are difficult to remove and install. I replaced all of mine with looser-fitting translucent plastic caps and the eyeguard doesn't move when installing or removing the cap.
  6. No. That is the Tirion Sky Atlas 2000.0 Field Edition, which prints the sky on 26 charts. Uranometria 2000.0 prints the sky on 220 charts (2x that in edition 1), a hugely larger scale.
  7. But, far less readable at night than black writing/stars on a white page.
  8. The Altair would be a noticeable upgrade, but a caveat: It has a very long eye relief. Even with the eyecup raised, which you would do if not wearing glasses, it is possible to get too close to the eyepiece and get blackouts therefrom. You do need to "hover" over the eyepiece.
  9. Yes, a fraud site. Unless it's used, no one sells a product below manufacturing cost. This is only one of many such sites. Like the Nigerian Prince scam we all avoid, in the modern world there are scammers in every field.
  10. Sale or no sale, I just wish they were available, period. There is so much pent-up demand.
  11. In spotting scopes, it's important to keep straight lines straight across the field. So a design for a spotting scope eyepiece would reduce rectilinear distortion to a minimum, leaving in angular magnification distortion at the edge. For astronomy, it's more important to maintain the same size and separation of points across the field, so angular magnification distortion is reduced to a minimum, leaving in a fair amount of rectilinear distortion. Tracking scopes seem to tolerate both forms of distortion, while scanning scopes usually prefer a very low RD. But, distortion is dis
  12. Simple drift timing will yield the true field and the field stop, but not the apparent field. There is an easy way to measure the apparent field: https://www.cloudynights.com/topic/574401-an-easy-way-to-measure-apparent-field-of-view/?p=7959408 and the posts that follow. Measure carefully, and you can easily get within 0.5° of apparent field.
  13. I can't tell you what will or won't be visible in white skies, but in a B2-B4 environment, every object can be seen in a 100mm refractor.
  14. In a nutshell: the smaller the exit pupil, the more problem you'll have with floaters on the Moon and planets. Floaters are not usually a problem on stars.
  15. Your pictures show normal amounts of rectilinear distortion in the form of pincushion. Distortion of this type means the timing of a star across the field will likely yield a field stop that, in turn, yields a smaller apparent field than the one seen. The outer edge of the field is stretched radially, as is the case with pincushion distortion. It is quite normal. A 48mm field stop is a bit large for a 42mm eyepiece, indication they accepted a small amount of vignetting as a compromise. A 65° field calculates to a 47.65mm field stop. 48mm translates to just a li
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