With a sturdy mount and tripod (see previous post), I was able to spend more time on targets that I know in order to determine the limits of this “hobby killer” department store telescope. My motivation was a discussion on The Sky Searchers board centered on another newbie who posted questions about the limits of his Svbony SV501 70mm f/6 (F=420 mm) refractor. Two stalwarts insisted that a “a good 70-mm” could split the famous double-double system epsilon Lyrae. He could not do that. I could not either with my 70 mm f/10 F=700 mm. So, the problem is: Is this “a good 70-mm”? My final judgement is that given the return-on-investment (ROI) for the price, it is good enough.
[07 November. After working with two other 70-mm telescopes in the same price range, and after working with another, newly-purchased National Geographic, I believe that that product does not perform competitively.]
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| Three versions of the National Geographic 70 mm refractor offered by Explore Scientific. Walmart is not alone in pricing it at $145 and out-of-stock. |
I started with two entry-level “First Scope” oculars from Celestron, a 12.5 mm and a 6 mm for 56X and 116.6+ respectively, both 50-degree field of view. I believe that these are Kellner designs, not Ploessl, (three lenses not four) just because they are inexpensive. I took one apart as far as I could conveniently, but never got down to the basic components and I left it at that.
21 Oct 20:45 (CDT UT -5)
Venus. Noticeably just past quarter phase. Chromatic aberration (CA) red to right blue to left worse with these and less pronounced with Celestron 17-mm and 8-mm Ploessl. More CA with Celestron 2X Barlow and 17-mm.
Jupiter. Less CA. Two bands. Four moons. No problems. But seeing is not good. Nominally clear but obviously poor sky high up. I quit early.
22 Oct 17:20 Forecast is clear through 03:00 hours.
Set up on Venus. CA depends on centering: blue to right, red to left; red to right purple to left. Worse with Kellners than Ploessls but both about the same and noticeably less than last night.
19:52 after some searching found Messier 22 in Sagittarius. Very faint.
20:02 Albireo. Smaller blue on top of larger yellow. Yellow about twice the size of the blue.
20:15 Test on epsilon Lyrae. No joy with both 12.5 mm and 6 mm oculars. I was able to see the first double, of course, but could not split their companions.
20:29 switched to TeleVue Nagler 7 mm Series 1 eyepiece. This is a high value, wide view 82-degrees, that I acquired on close-out from Enerdyne in Suttons Bay. (It had been on the shelf unsold for four years and was now outdated by new designs from TeleVue.) No change. Same view as 6-mm Kellner.
(It is important to let your eyes left and right take long turns viewing as the sky changes, shimmering, clearing, worsening, etc.)
Changed to 6-mm Kellner with 2X Barlow. (700/3 = 233.3+ X).
Right pair is more pronounced. I can make out the companion above.
23:13 hours - Second companion is still not there. It should be to the left but is not.
23:13 Checked eta Cassiopeiai double star 12.5 mm (56X) with no problem.
I spent the rest of the night not photographing the Moon and Jupiter with my Explore Scientific 102-mm refractor and my iPhone 11. I closed up shop at 02:00 on 23 October 2021. The ES 102 is a nice scope. It is my grab-n-go. But it has a design problem in that the draw tube does not allow a shorter focus with more than a basic lens in the diagonal. I had the same problem trying to view Venus with two filters to cut the glare. (The Natl G worked just fine.) So, none of the 50 snapshots was publishable.
PREVIOUSLY ON NECESSARY FACTS
The Philosophical Breakfast Club
Science Fair: A National Geographic Film
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