The spotting scope (a small refractor, right?) on my cat presents an inverted view. I.e. it is upside-down. Or rotated. Up is down and left is right. Or to put it yet another way, south is up. I verified this in the day with a terrestrial target, my Mountain Equipment Co-op Pingo tent.
Drawing of view of my tent logo through eyepiece of finder and newt.
Mom's newt reflector presents the same view through the eyepiece... It's upside-down or rotated. So, when trying to find things by star chart, I simply need to turn the chart upside-down. Or view from the other side of the table.
When I through through the cat telescope, with the standard mirror diagonal or star diagonal of course, I see a laterally-inverted or mirror-reverse view. I'd have to hold a mirror to the charts or look at the backside of them brightly backlit.
Drawing of view of my tent logo through eyepiece of cat with mirror diag; this also assumes I'm looking "down" into the eyepiece from above the 'scope, so to get a "reference" to the real horizon.
OK. The book says, "Inverted images [are] seen in Newtonians." Later, "[But] mirror-reversed views [are] produced by refractors and catadioptric telescopes."
I find this especially ironic when they're at the same time addressing the surprise and frustration people experience regarding this.
The Sep/Oct issue of nightsky magazine, on p.83, offers the following: binos offer a correct, upright view. Interestingly, they also show a refractor with a 45° diagonal here. A compound telescope (they show a cat) or a refractor, both with a 90°, presents a mirrored view. And finally the finder scope or a reflector (or as noted in their text, a "straight-through" refractor) creates an upside-down view.
§
Perhaps it is not an error. But the remark that a refractor produces a laterally-inverted or mirror-reversed assumes that a mirror diagonal is being used. That's common. It's standard equipment on a SCT or MCT. Still, I think it should be stated for clarity.
No comments:
Post a Comment