rod

Oct 22, 2019
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FYI, your 50-mm refractor telescope will help in observing the planets. You should not try and focus on a planet above 120x views though because of the size of your primary mirror, about 2-inches, 50x to 100x views will show various details for planets like Venus, Mars, Jupiter, and Saturn. Starry Night software, SkySafari, those applications allow you to set the sky view for your specific location and local time. Stellarium works well too, I use Starry Night and Stellarium. Here is the link for Stellarium 0.20.0, the latest version. It is freeware, http://stellarium.org/
 
Jan 24, 2020
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FYI, your 50-mm refractor telescope will help in observing the planets. You should not try and focus on a planet above 120x views though because of the size of your primary mirror, about 2-inches, 50x to 100x views will show various details for planets like Venus, Mars, Jupiter, and Saturn. Starry Night software, SkySafari, those applications allow you to set the sky view for your specific location and local time. Stellarium works well too, I use Starry Night and Stellarium. Here is the link for Stellarium 0.20.0, the latest version. It is freeware, http://stellarium.org/
I have 20mm and 12mm eyepiece? What magnification do they produce? Do they match the value with yours?
 
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rod

Oct 22, 2019
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The rule of thumb is that the eyepiece with the larger mm size will provide a lower power view and generally, wider field of view too and brighter image in the eyepiece. My 90-mm telescope has a focal length of 1000 mm. An eyepiece with 10-mm focal length will provide a 100x view. If your 50-mm telescope has 900-mm focal length, the 20-mm eyepiece shows a 45x view, the 12-mm shows 75x. Just find the focal length of your 50-mm telescope and divide by the focal length of the eyepiece.
 

rod

Oct 22, 2019
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Praynay, the eyepieces have a published apparent field of view too in degrees for the different models. Example, an eyepiece with 50 degree apparent field of view (common with a plossl type). If that eyepiece provides 50x with your telescope, that is 50/50 = 1-degree true field of view in the eyepiece when you look through it.
 

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