When I first added my C8 telescope, I saw the default settings showed as Left/Right Mirrored and Up/Down Normal. Which seemed fine. Assuming one has a mirror (or star) diagonal attached to a Schmidt-Cassegrain telescope into which the eyepieces are inserted, the view is mirror-reversed. Up is up but left is right. Another assumption, of course, for that view is that the user is standing above or over the telescope looking straight down into the eyepiece. When the mirror diagonal is rotated, things changed. But that's a different issue.
Over time I added many telescopes to SkyTools. Occasionally, usually later, I would find some settings odd or inappropriate. Or I'd noticed the eyepiece view was incorrect. I made adjustments along the way and didn't think much about it. But over the last couple of months, something was bugging me.
Perhaps it was going through the software installation process again, back in August for the John Charles computer, and then after Thanksgiving for the John Phil portable computer, that it really caught my eye: some of the telescope presets appear to be wrong.
Ironically, the Televue 101 entry which is active by default, does not seem right. In particular, the Televue 101 preset has the Up/Down set to Flipped. When it should be Normal.
And when I recently went to add a telescope entry for Ian's 20" home made Dobsonian and Thierry's 10" LX 200, that's when I really paused. I don't remember now, exactly, the steps to add the Dobsonian. I might have chosen the Home Made Dob 12.5 f/5 as a starting point. Or maybe the Obession 18 f/4.5. Both of these reflectors have the view options set as Left/Right Normal and Up/Down Flipped. That's not right. The view in a reflector is rotated. Turned 180°. Up is down, left is right. That requires the settings to be Left/Right Mirrored and Up/Down Flipped.
If one consults the Help page for the Add/Modify Telescopes Dialog for assistance, the following is noted:
Click on the Left/Right: Mirror/Normal and Up/Down: Flipped/Normal hypertext to set the scope's natural orientation as seen in the eyepiece. For instance, a Newtonian reflector will typically show a view that is a mirror image (left and right reversed) and inverted (up and down reversed). For such a scope you would select Left/Right to be mirrored and Up/Down to be inverted.I find it a little curious, as an aside, that the descriptive help text changes terminology when referring to the Up/Down setting, using "inverted" instead of what is in the system, "flipped."
Regardless, my logic seems to hold up. The Left/Right and Up/Down settings should be configured, as follows, for the respective telescope design. This assumes that refractors and SCTs (and MCTs) are normally used optically with a mirror diagonal.
- refractor: Mirrored and Normal
- reflector: Mirrored and Flipped
- SCT: Mirrored and Normal
I could imagine there a couple of exceptions, based on an unusual telescope design. For example, I don't know what TMB telescopes are. And I don't know what all the 'scopes come with. Perhaps some ship with a image erecting diagonal as standard equipment.
Still, there just seem to be errors. For example, there are four Home Made presets. All have Mirrored and Flipped except for one. That looks like an oversight. All the Meade LX-200 'scopes have Mirrored and Flipped. One must use a mirror diagonal with a fork mounted telescope... That looks like an error copied from one profile to seven others.
This was an eye-opener. I had simply assumed that the presets were correct. That everything would be fine if I used one of the built-in telescope entries.
Now, I won't make assumptions.
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