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Refractor image

Fri Oct 19, 2018 2:36 pm

Hi, I am a bit confused doing some research to get by first telescope. As I want something portable and easy to set up I'm leaning towards maybe a 4inch refractor. I understand that the image will be upside down but reading some sources they suggest the image may also be a mirror image.Now I think I can cope with an upside down image for star hopping but not too sure about mirror image on top of upside down.
Is this mirror imaging correct or is it model, lens or diagonal specific?

Re: Refractor image

Fri Oct 19, 2018 3:08 pm

paul.r.byrne@gmail.com wrote:Hi, I am a bit confused doing some research to get by first telescope. As I want something portable and easy to set up I'm leaning towards maybe a 4inch refractor. I understand that the image will be upside down but reading some sources they suggest the image may also be a mirror image.Now I think I can cope with an upside down image for star hopping but not too sure about mirror image on top of upside down.
Is this mirror imaging correct or is it model, lens or diagonal specific?

Hi Paul and welcome

If not using a diagonal, the image will be upside down and left-right reversed.
If using a 90 degrees diagonal, the image will be restored upside-up, but still be left-right reversed.
A 45 degree diagonal will restore to 'correct' view as would be used for terrestrial use.

Finders can come in as straight through, 90 degrees or RACI (right angle, correct image) which is equivalent to the 45 degree, but with the eyepiece at 90 degrees to the optical axis.

If you're using for star hopping, and you are printing you own star hopper charts from software, you can reverse the images (as appropriate for your finder) before printing them off.
Remember that your initial hopping is likely to be done with the finder, so you'll want to have your 'finder' charts aligned appropriately.

I use Cartes de Ciel to prepare finder charts like this in Word, CdC has controls to flip the image vertically and horizontally (use both for Straight Through finders).
CdC (as will other software) allows you to create field of view indicators for your finder and for various eyepieces
M27 Finder.PNG
M27 Finder.PNG (146.89 KiB) Viewed 1319 times

Hope this helps.

Re: Refractor image

Fri Oct 19, 2018 6:11 pm

Many thanks for the detailed and easy to understand answer. Much appreciated

Re: Refractor image

Sat Nov 10, 2018 11:27 pm

Honestly, a 4" refractor is not particularly portable. I have a 127mm Maksutov, which is much lighter. However, even that is too heavy to carry by air, if that is what you are thinking. When I travelled a lot for work, I used 15x70 binoculars or a Startravel 80. They have been around the world a few times, as has my Coronado PST.
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