Binocular Sky Ratings
Scoring equipment is fraught with difficulties and inconsistencies; I am fully aware that others may disagree with the scoring system I use: the reason for publishing this detailed description is that it enables you to at least compare items I have reviewed and, if you wish, "transpose" it to a scoring system that you like.
- These are scores out of 10, based on the guidelines below; intermediate scores allow for nuance.
- Whilst they aim to be objective, it is inevitable that there will be some subjectivity.
- To obtain the Overall score, Optical:Mechanical:Accessories:VFM are weighted 5:4:2:4
- I do not give a score for brightness, because this would not be testable under consistent sky conditions and may therefore be misleading. It is also only relevant when comparing binoculars side-by-side; if I have done such a comparison, it will be noted in the text of a review.
Sharpness of Image This is based on the ability to split a double star at the centre of the FoV when the binocular is mounted. The star used will normally be chosen so that:
- 300 ≤ separation in arcseconds x magnification ≤ 400
- 5 * log10(aperture in mm) - 4.5 ≤ magnitude of primary star ≤ 5 * log10(aperture in mm) - 1.5
- Difference in magnitudes ≤ 2.5
- 10 Easy split, clear dark space between components
- 8 Easy split
- 6 Clearly split
- 2 Star looks elongated
- 0 Blurred
Size of usable field
This is the size of the field within which the image of the double star above does not begin to break down:
(% of field * True FoV * Magnification / 600)
(Yes, I do realise that based on this some top-end binoculars like the Swarovision EL 10x50 would have a score of 11/10 :-) )
Colour correction This is based on perceived colour from the lunar limb between 1st and last quarters.
- 10 No false colour with the limb anywhere in the FoV
- 8 No colour on axis; perceptible off-axis
- 6 No or minimal colour on-axis, obtrusive off axis
- 4 Colour noticeable but not obtrusive on-axis
- 0 False colour obtrusive on-axis
Control of stray light This is based on spurious reflections from the Moon between 1st and last quarters.
- 10 No spurious reflections with the Moon anywhere in or outside the FoV
- 8 Minimal with the Moon inside the FoV, noticable with it outside the FoV
- 4 Minimal with the Moon inside the FoV, obtrusive with it outside the FoV
- 0 Obtrusive with the Moon inside and outside the FoV
Eye relief
- 10 All spectacle users will easily see the entire field of view
- 6 May be a bit tight for some spectacle users
- 3 Only usable without spectacles
- 0 Field of view not visible without spectacles with eye-cups in extended position
IPD
- 10 Suitable for a wide range of faces
- 8 May be unsuitable for unusually large or small adult faces/wide noses
- 4 Unsuitable for some normal-sized adult faces
- 0 [Unlikely to be met]
Focus mechanism
- 10 Smooth throughout its range, precise, does not slip in use.
- 8 Some 'stiction' if it has not been used for a while, otherwise smooth throughout its range, does not slip in use.
- 5 Some 'stiction' if it has not been used for a while, stiffness feels uneven, does not slip in use.
- 0 Jerky/sticky, difficult to get precise focus, slips during use.
Right Eyepiece adjustment 'Properly set' means that it is at its zero/central position when used with properly corrected vision.
- 10 Easy to adjust, does not slip in use, properly set
- 8 Easy to adjust but with some stiction if it has not been used for a while, does not slip in use, properly set
- 5 Difficult to adjust but does not slip in use, setting tolerable
- 0 Slips in use or so poorly set so that it is impossible to simultaneously focus both eyepieces
Eye cups
- 10 Twist-up, intermediate click stop(s), no slippage under pressure
- 8 Twist up, no slippage under pressure or Fold down, appropriate length, comfortable
- 3 Difficult to fold or twist/inappropriate length/uncomfortable/slip in use
- 0 None
- 10 Smooth throughout its range, does not slip in use
- 8 Some 'stiction' if it has not been used for a while, otherwise smooth throughout its range, does not slip in use.
- 6 Some 'stiction' if it has not been used for a while, stiffness feels uneven, does not slip in use
- 3 Feels tight/uneven/jerky but does not slip in use.
- 0 Jerky/sticky, too loose and slips during use
Armour
- 10 Substantial, offers good protection, comfortable to hold
- 6 Minimal, offers some protection, comfortable to hold
- 0 Absent or uncomfortable
Weight and balance (Applies to binoculars up to 10x50 only) This is obviously somewhat subjective and is comparative to other binoculars of the same or similar size.
- 10 Easy to hold steadily
- 8 Can be held steadily
- 5 Feel uncomfortable
- 0 Too heavy or poorly balanced to be held steadily
Case
- 10 Waterproof hard case with foam cushioning
- 8 Hard or rigid case
- 6 Soft case, well-padded.
- 4 Soft case with minimal padding
- 0 No case
Neck-strap
- 10 Padded wide neckpiece
- 8 Wide unpadded neckpiece
- 3 Thin strap with no neckpiece
- 0 No strap
Objective caps
- 10 Tethered,well-fitting
- 8 Untethered, but fit well and do not easily fall off/tethered but poorly fitting
- 4 Untethered and fall off too easily
- 0 None
Eyepiece Caps/Rainguard
- 10 Tethered, fits well, does not restrict IPD
- 8 Tethered, restricts IPD / Untethered, fits well
- 4 Untethered, fits poorly
- 0 None
Value for Money My subjective opinion.
