Table listing scopes with realistic lense calcuations?

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TSS_ASTRO
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Table listing scopes with realistic lense calcuations?

#1

Post by TSS_ASTRO »


Hi All,
I've been building an Excel sheet - with a table of my lenses and their Exit Pupil and Mag calculations - for the two scopes I mainly use.
The Celestron 8" SCT, and the Orion 10" Dob

After putting this together, I started to think about adding other scopes, such as a 6 or 8 inch dobs - with their specs - just to see what exit pupils and magnifications to expect.

But then I wondered if someone has already done this.
Anyone know of a table listing this type of data for the most popular types of scopes?

Thanks in advance!
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Re: Table listing scopes with realistic lense calcuations?

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Post by SkyHiker »


I doubt if there is such a table because it depends on a combination of the eyepiece and the OTA / primary objective. Everyone has different eyepieces and primaries so the table would only be useful for one individual. Which can still be useful, of course.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Table listing scopes with realistic lense calcuations?

#3

Post by KathyNS »


A simple rule of thumb allows you to calculate magnification and exit pupil in your head.

For all scopes, useable exit pupils range from 1mm (high magnification) to 7mm (low magnification). Take the scope's aperture in millimetres and divide by the exit pupil you wish to use. That indicates the magnification. So any 8" (200mm) scope will give useable magnifications of 200x down to 29x.

And, in an astonishing stroke of luck for those who like to do calculations in their head, you can calculate the focal lengths of the eyepieces that will give you those magnifications by multiplying the scope's focal ratio by the exit pupil. So an f/4 scope can use eyepieces from 4mm to 28mm.
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DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,Oiii,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier); Helena Observatory (H2O) Astrobin
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