which way up?!

[F1Bird]

Sorry to be so useless but can someone please help me figure out which way is up through my 2 eyepieces?! I have a 20mm self erecting eyepiece and a 10mm eyepiece which came with my scope as standard. I think the 20mm shows the view through the eyepiece as it is to the naked eye (at least it did in the daytime). Will the 10mm just be inverted or does it flip along the vertical axis? The reason I'm confused is that I really struggle to identify stars through the 20mm eyepiece as nothing appears as it does to the naked eye. I think I found the Orion nebula just now but couldn't seem to find Rigel in the place that I thought it should be! I was probably in the wrong place entirely as I haven't stuck my Quikfinder onto the scope yet!

[JamesF]

What sort of telescope is it? Refractor? Newtonian? Mak? SCT? Difference types of telescope produce images different ways around.

James

[F1Bird]

It's a celestron astromaster 114. The one with the comedy star pointer!

[Peter Drew]

All common forms of astronomical telescopes with just an eyepiece fitted give the same field orientation when looking due Sout at night, upside down and left to right reversed. The difference occurrs when a diagonal or erector system is added between the telescope and the eyepiece. A right angle diagonal produces an upright image but with left and right still reversed, a 45 or 90 degree diagonal with a roof prism will give a terrestrially correct image. A PST uses a pentaprism and although it turns the light through 90 degrees the image is still upside down and left to right reversed.

[Scooot]

The Sky Safari App might help you. If you tap the top right of the screen in sky safari a menu pops up that allows you to flip the screen to view the sky the same way around as the view through the eye piece.

This is a zoomed view of Jupiter with sky flipped, as you'd see it through a reflector tonight.

[JamesF]

All common forms of astronomical telescopes with just an eyepiece fitted give the same field orientation when looking due Sout at night, upside down and left to right reversed.

That's not true for a Mak or SCT, is it?

James

[ianfiat]

It's a celestron astromaster 114. The one with the comedy star pointer!

Its not funny, its tragic

[acey]

A Newtonian reflector (like the Astromaster) will normally give an inverted image, with no left-right reversal. In other words a rotated image, so you just need to turn a star map round to the right angle to match what you see through the eyepiece. Check the 10mm eyepiece in daytime. You ought to find the view approximately upside-down, or at any rate rotated through an angle close to 180 degrees.

At night, point the telescope at some stars and watch through the eyepiece without moving the scope. Stars will slowly drift out of the field of view. The direction in which they are drifting is celestial west. On a star map, north is at the top and west is at the RIGHT (opposite from what we're used to on ground maps). So when you look through the eyepiece, West is where the stars are heading and North is 90 degrees anticlockwise from that. Turn your star map to match those directions.

The view through the finder should be inverted (rotated), like the view through the eyepiece, though it probably won't be rotated by exactly the same amount, so the views through finder and eyepiece will appear slightly rotated with respect to each other (and at different magnifications, obviously). When first aiming the scope, you want to rotate your star map to match the view through the finder. Since stars move very slowly across the finder's field of view, it might be difficult to establish where west is, but you may be able to match the pattern of stars seen in the finder with the pattern of stars on map, just by turning the map.

All of this is assuming that your scope is a regular Newtonian. I believe it has a built-in Barlow, but that shouldn't affect things.

[Peter Drew]

JamesF. Yes that holds true for Mak's and SCT's if used straighthrough. There are some Mak variants that differ which is why I was careful to state "common".

[JamesF]

JamesF. Yes that holds true for Mak's and SCT's if used straighthrough. There are some Mak variants that differ which is why I was careful to state "common".

I'm going to have to go and check this now. It's one of those things you often don't notice I guess. I have a feeling that with an eyepiece I get a left-right inverted image with my Mak, but when I put the DSLR on then I don't. I know I never invert my lunar images, so I shall have to try it in the field and see what happens.

James

[acey]

Left-right reversal is just a function of how many mirrors are in the optical train. If it's an odd number then you've got reversal, if it's an even number (including zero) then you don't. A refractor with mirror-diagonal gives left-right reversal, a Newtonian (which has two mirrors) does not. Upside-down inversion of image is what you get from lenses, and is equivalent to a rotation of 180 degrees.

A Cassegrain has two mirrors and so produces no overall left-right reversal; the image is upside-down as with a refractor, but if you use a mirror diagonal then the image will be upright and left-right reversed, as with the refractor.