Both are 42 mm; they are not the same complete design
The first number is nominal magnification; the second is the objective diameter in millimeters. In this comparison, both have 42 mm objectives while magnification changes from 8× to 10×. [N18] [N19]
The ratio 10 ÷ 8 is 1.25: the nominal angular image scale is 25% larger at 10×. That calculation does not mean 25% more resolved detail, 25% more useful range or a 25% better product. Those conclusions would require evidence about the finished instrument and observing conditions.
Even within one range, the eyepiece design, eye relief, body dimensions and field can differ. Across different brands and prices, still more variables change. Keep the model names attached to every specification comparison.
If you prefer 8× but are deciding how much to carry, see 8×32 vs 8×42 binoculars. That comparison changes objective size while keeping magnification the same.
What to prioritize in your own use
| Your priority | Our starting suggestion | Check before deciding |
|---|---|---|
| Finding subjects quickly | Begin by trying an 8×42 with a suitable real field | An individual 10× design may still provide enough field |
| A larger view of a distant, relatively steady subject | Compare a 10×42 directly with 8×42 | Does the larger image remain steady and reveal useful detail? |
| Glasses-friendly viewing | Ignore the power ranking at first | Actual eye relief, eyecup design and your eyewear |
| Frequent handheld use | Give comfort and control high weight | How each instrument behaves during a realistic session |
| Lower-light observing | Check the whole optical and eye-fit situation | Do not choose from a calculated brightness number alone |
| A major step beyond handheld reach | Revisit the type decision | A supported scope may be a different, more relevant route |
These are conditional starting points, not rankings based on a user trial we have conducted. Your hands, eyes, posture and targets can change the outcome.
Real field and apparent field answer different questions
Real field of view describes how much of the outside scene is covered. Apparent field of view describes the angular span the view appears to occupy through the eyepiece. Do not use one as a substitute for the other. [N10]
This distinction matters when reading “wide angle.” A higher-power model can have a wider apparent field but cover a slightly narrower real scene. That is not necessarily a contradiction.
For finding a subject, use the real-field figure and the actual handling. For the visual impression at the eyepiece, apparent field is also relevant. When comparing linear fields, keep the stated viewing distance and units consistent. A width in feet at 1,000 yards is not obtained simply by turning a width at 1,000 meters into feet.
A same-series example: Nikon PROSTAFF P3
The following are manufacturer-listed specifications, not our measurements or an overall recommendation. They were checked on October 16, 2026. [N08]
| Specification | P3 8×42 | P3 10×42 |
|---|---|---|
| Objective diameter | 42 mm | 42 mm |
| Real angular field | 7.2° | 7.0° |
| Apparent angular field | 53.4° | 62.9° |
| Eye relief | 20.2 mm | 15.7 mm |
| Close focus | 3.0 m / 9.8 ft | 3.0 m / 9.8 ft |
| Weight | 575 g / 20.3 oz | 585 g / 20.6 oz |
| Eyepiece spacing adjustment | 56–72 mm | 56–72 mm |
In this pair, the 10× has the larger apparent-field figure while the 8× covers a slightly larger real angle. Some other specifications stay the same, while eye relief differs. The point is to inspect the table—not to assume that every 8×/10× pair has these differences. [N08]
The table does not measure edge sharpness, glare, alignment or personal comfort. It cannot tell you that one is better merely because more of its numbers look larger.
Exit pupil is useful, but not a finished-image brightness test
Using nominal aperture divided by magnification:
42 ÷ 8 = 5.25 mm for 8×42; 42 ÷ 10 = 4.2 mm for 10×42.
Those are calculated exit-pupil diameters. A manufacturer may round the first to 5.3 mm. They are not measured light-transmission percentages. [N02]
A larger exit pupil can be useful in some lower-light or eye-position situations, but the observer's pupil and the instrument's transmission also matter. Nikon expressly distinguishes calculated relative brightness from the actual image, which can differ with optical quality and coatings. [N01] [N03]
Do not turn the squared ratio into a universal claim that an 8×42 view is a particular percentage brighter to every person. Equally, do not assume that the smaller 10× exit pupil makes daytime use unsuitable. The practical question is whether the specific view works for your conditions.
Fit and holding can outweigh a small power increase
Longer listed eye relief can make a model worth trying with glasses, but effective fit still depends on eyecups, lens position and your eyewear. Inspect the whole field in your normal setup rather than accepting an eyeglass-friendly label as a guarantee. [N11]
Check eye spacing and focus adjustment too. An incorrectly adjusted binocular is not a fair demonstration of its magnification. Nikon's center-focus instructions separate eyecup position, interpupillary distance and diopter adjustment. [N13]
For a handheld trial, use a posture you will actually adopt, not only a shop counter that supports your elbows. Start with ordinary safe targets at a useful distance. Notice whether the increased image scale helps you observe or mainly magnifies your movement. Nikon's power-selection advice identifies steadiness as a reason to consider lower magnification. [N09]
A five-question choice, not a universal winner
Try to answer these in order:
- Can I fit and focus both correctly?
- Can I find my typical target without unnecessary searching?
- Can I hold the view well enough to use the apparent detail?
- Does 10× reveal information I genuinely need compared with 8×?
- Would either change how often I carry and use the binoculars?
Choose 10× when the added image scale produces a worthwhile benefit for you without unacceptable fit or handling costs. Choose 8× when it better supports acquisition, comfort or repeated handheld use. Neither answer needs a claim that the other power is poor.
If your current 8×42 already does the job, 10×42 is not an automatic upgrade. If neither supplies the distant detail you need, revisit binoculars versus spotting scopes rather than expecting a modest power change to solve every limitation.
Solar safety
Never aim ordinary optics at the Sun without correct instrument-specific front-mounted solar filters. Eclipse glasses behind unfiltered optics are unsafe. Consult expert solar-observing guidance. [SAFE02]