Celestron HD 8
Celestron HD 925
Celestron C 11
Mes télescopes et jumelles:
150mm F5 Newt on EQ5, 127mm Mak Cass on AZ4
Oberwerk BT70-45 and 15X70 SkyMasters
Quote:Refractors are inverted as well. A diagonal will flip the image in one axis so that it is vertical but still reversed left to right. For terrestial viewing you need an Amici or Porro prism that will give you a correct image.
Quote:Is a refractor telescope the only one that will show a right side up image view? Or, does it show upside down? I know reflectors are inverted, but refractors are all right side up, no? What about the cat design, aren't they still reflectors, thus upside down view?If a person wanted a scope for both celestrial viewing and horizon viewing, he would be stuck with a refractor, right?
Quote:Most refractors come with a standard prism or mirror diagonal which will give you a vertically corrected image, but horizontally inverted.
Quote:Is a refractor telescope the only one that will show a right side up image view? Or, does it show upside down?
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Quote:All scopes invert and reverse the image, refractors and Cats (SCTs, Maks etc) can be used with diagonals which invert one direction.
Quote:The diagonal/mirror is part of the design of the ETX scopes I believe, as you can't view straight through, the EP port is perpendicular to the optical path.
Quote: You're saying "can be". Does that mean I should not assume any scope has a diagonal in it? I guess what I'm trying to get at is, if I were to see an ad for a refractor scope that I was interested in, I still should not assume it will have the prism or diagonal mirror in it, correct?
Quote:Reflectors show images upside down -- or as I would prefer to state that, rotated 180 degrees. As though you took a book and rotated it so the print is facing down, not up.
Orlando, Florida, 81° W, 28.5° N, Joined: 8/27/11
CGEM, C8, C11, AT72ED, NexStar 5SE
Orion Starshoot Pro V2 Color, NexImage 5 / ASI120MC Planetary imagers
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Quote:If the number of reflecting surfaces is odd then you will have a mirror image.Without a diagonal:A refractor has zero reflecting surface and a Newtonian or SCT has two reflecting surfaces (two and zero are both even). The image will be upside down.With a diagonal:A refractor has one reflecting surface and a Newtonian or SCT has three reflecting surfaces (one and three are both odd). The image will be right-side-up but a mirror image.With a 45 Degree Angle Erect Image Diagonal:Somehow this manages to add 2 reflecting surfaces while rotating 180° which makes everything right-side-up AND not a mirror image.Here is a 45° diagonal.Note that people generally use a diagonal on refractors and SCTs but not on Newtonians.
Quote:When we talk about diagonal, are we just talking the angle of the eyepiece?
Quote:So, just out of curiosity, can a star diagonal be used on a reflector, just to get things right side up if you wanted?
Quote:Quote:So, just out of curiosity, can a star diagonal be used on a reflector, just to get things right side up if you wanted? Yes.If you use a 90° star diagonal on a reflector the image will no longer be upside down but you would then have a mirror image.If you use a 45° star diagonal on a reflector the image will no longer be upside down and you would NOT have a mirror image.If you use a star diagonal on a reflector you would have to position your head higher up and you would then be looking down. You might then be tempted to rotate the star diagonal 90 degrees. In that case your image would be half way between being upside down and right side up, i.e. your image would be rotated 90 degrees.
Quote:I forgot to mention that reflectors tend to have less back focus so you might not be able to focus when using a diagonal. If you design your reflector to have more back focus then the secondary mirror would have to be closer to the primary mirror and at that point the secondary mirror would have to be larger. This would block more light so this is why they don't do that.