FAST LIGHT COL­LEC­TION

Sky at Night Magazine - - FIRST LIGHT -

The 210mm par­a­bolic pri­mary mir­ror at the heart of the PN210 Mk II works at f/3.8. This is con­sid­ered a fast fo­cal ra­tio, a pho­to­graphic term that es­sen­tially de­scribes how quickly a cer­tain depth of im­age can be de­liv­ered. One ma­jor ben­e­fit of a fast sys­tem is that ex­po­sure times can be kept rel­a­tively short. This also goes hand-in-hand with the ex­cel­lent porta­bil­ity of the te­le­scope. Trans­port it to a dark-sky lo­ca­tion and even with mod­er­ately ac­cu­rate po­lar align­ment, it should be pos­si­ble to take rel­a­tively short but still quite deep ex­po­sures.

The 800mm fo­cal length of the pri­mary mir­ror de­liv­ers a fairly wide field of view at prime fo­cus. Us­ing a Canon EOS 6D, a full frame DSLR, our im­ages cov­ered a sky area 2.5x1.5°. Con­se­quently, the fast, wide-field de­liv­ery of the PN210’s op­tics makes it best suited for the imag­ing of ex­tended deep-sky ob­jects.

Be­ing a New­to­nian re­flec­tor, the PN210’s field does suf­fer from coma, which be­comes very no­tice­able to­wards the edge of frame, es­pe­cially when us­ing a cam­era with a large sen­sor. A match­ing field flat­tener is rec­om­mended to re­duce this is­sue.

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