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Novice Challenge

Newtonian for astrophotography

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Hi! I am new to astrophotography.

I know that doublet or triplet refractor are most used for astrophotography because they remove chromatic aberration.

But newtonians also prevent aberration. I know that newtonians are big and bulky to use, but small 80mm, low f/ number newtonians are also available. So why these small newtonians are not used for astrophotography despite they prevent aberration, are small in size, and are also cheap ?



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A small Newtonians clear aperture ratio compared to its central obstruction will be lower than a larger aperture Newtonian (the central obstruction blocks out light being received). Mirror quality as well as telescope construction also has a factor on Newtonian prices.

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Its not quite correct to say that a newtonian prevents aberrations, its just that a newtonian does not suffer from chromatic aberration. Newtonians with a parabolic primary mirror do however suffer from coma, which requires a coma corrector to get rid of and here its not so simple as just get any coma corrector and the coma is gone. There are different types of coma corrector and not all of them do a good job, basically you're looking at twice the price of the scope in some cases for a competent coma corrector alone and if you go for one of the really cheap ones you can expect to exchange coma to some other aberration like astigmatism and/or spherical aberration. Cheap newtonians can also have large amounts of spherical aberration in their primary mirrors, which will not be solvable with any corrector.

You also need a 2'' focuser to use a coma corrector, which is something that is really not viable for very small newtonians. For astrophotography the 130PDS is a great first purchase.

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