Binoculars for Stargazing Why binoculars Cost From as
Binoculars for Stargazing
Why binoculars: • Cost: From as low as £ 20 -£ 30 you can get a decent pair of binoculars. • Wide Field: Binoculars provide different views compared to telescopes: low power, wide fields, excellent for star fields. Can be breathtaking under dark skies. • Ease of Use: Just hold them in front of your eyes. Also, an easy connection with what you see with your eyes. • Portability: Can be with you almost always.
What you can see:
Basics: Aperture & Power • “ 10× 50” = 10 x magnifying power, 50 mm aperture. • For astronomy: at least 35 -42 mm aperture (birdwatchers love these sizes) 50 mm or more preferred (size & cost define our upper limit). • Too much power is bad – too dim & too hard to hold steady. Many people feel up to 10 x is OK to hold (I prefer 7 -8 x). • Avoid variable magnification / zoom binoculars (12 -20 x 80 etc). They are never good.
Basics: Exit pupil & Eye relief • Exit Pupil is the diameter of the light cone coming out of the eyepiece. Exit Pupil = Aperture / Magnification. Large exit pupil = bright image. Young people up to 7 mm exit pupil (e. g. 7 x 50) Older people perhaps up to 5 mm (e. g. 10 x 50, 8 x 40) • Eye Relief is the distance of your eye from the eyepiece. For eyeglass wearers, 12 mm or more are required.
Basics: Field Of View • Example: “ 315 ft @ 1000 yards”, “ 105 m @ 1000 m”, “ 6. 0°” • Apparent field of view = Fo. V° x magnification (e. g. 6. 0°x 10 = 60°) – similar to telescope eyepieces • At least 60° is “wide-angle”. Under 50° is rather narrow. ? ? ? ? ?
Basics: Prisms & Coatings • Porro prism better perf. /price for astronomy. Roof prism preferred for birdwatching (more compact, waterproofing), requires expensive phase-coatings for good stargazing. • Ba. K 4 glass better than cheaper BK 7 glass. • Full Multi Coated (FMC) > Multi Coated (MC) > Fully Coated (FC) > Coated (C) > No coating > Orange/Ruby “coating”
Tips for Evaluating Binoculars • Check for smooth operation of focuser, diopter and hinge. • Collimation: Make sure the two images from your eyes merge into one. New binoculars should be collimated. • Check for sharpness of focus, colours and chromatic aberration around bright objects.
Tips for Evaluating Binoculars 2 • Look through the eyepiece from a distance to check for undersized prisms and BK 7 glass (diamond shape). • You can measure the effective aperture using a single LED torch / flash at least 15 cm from the eyepiece + tissue paper. • Make sure you can easily view the entire Fo. V with or without eyeglasses (i. e. as you will be using them).
Buying Tips • Avoid zoom binoculars, anything with a red/orange coating, unknown brands (e. g. based on Amazon reviews) – some well known brands with decent budget bins are: Nikon, Olympus, Celestron, Opticron, Helios, Bushnell, Bresser, Meade… • Porro prism will give you better quality for the price for astronomical use. If you don’t have a limited budget, expensive roof prisms with phase coatings perform as well as good porro. • Astronomer favorites are 7 x 50 or 10 x 50, as those have the most aperture you can easily carry around and hold steady. • Astroboot (http: //www. astroboot. co. uk/) often has some good quality models at heavy discounts. • Lidl carries a couple of times a year usually a Bresser 10 x 50 for around £ 17. But test it first because many are uncollimated.
Examples up to 50 mm • £ 25 -£ 35: Celestron G 2 Porro 8× 40 / 10× 50, Bresser Hunter 8× 40 / 7× 50, Helios Solana 8 x 40 / 10 x 50. • £ 40 -£ 60: Opticron Adventurer 8× 40 or 10× 50, Celestron Cometron 7× 50, Olympus 8× 40 DPSi, Helios Fieldmaster 7 x 50 / 10 x 50. • £ 60 -£ 90 Nikon Aculon 8× 42 / 10× 50, Helios Weathermaster III WP 7 x 50 / 10 x 50 – Naturesport Plus 10 x 50 WA.
www. binocularsky. com
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