Binocular magnification
8x42 or 10x42 Binoculars: Which Should You Buy?
Quick answer
Buy the Vortex Diamondback HD 8x42 Binoculars at $239.00 for most uses: 8x gives a 5.25mm exit pupil against 10x's 4.2mm, and 8x is noticeably steadier to hold on target than 10x. Buy 10x42 only if the extra reach outweighs a dimmer image and more visible hand shake for your specific use.
Vortex Diamondback HD 8x42 Binoculars
$239.00A 42mm objective at 8x giving a 5.25mm exit pupil and a noticeably steadier handheld image, the better all-around choice for most users and most light conditions.
Best for: handheld glassing at dawn and dusk
Check price on Amazon Vortex Diamondback HD 10x42 Binoculars
$240.00The same 42mm objective at 10x giving a 4.2mm exit pupil and more visible hand shake at the eyepiece, in exchange for meaningfully more reach on a distant subject.
Best for: general hunting and glassing
Check price on AmazonBoth magnifications share the identical 42mm objective lens, which makes this one of the cleanest comparisons in binocular shopping: the only variable that changes is magnification, and every real difference between an 8x42 and a 10x42 traces back to that single number.
Two things change directly with magnification and nothing else: exit pupil, which controls how bright the image looks, and how much ordinary hand tremor gets magnified along with the target. Both point the same direction, and it is not the direction most first time buyers assume.
These figures are researched from published objective diameters and magnification specifications, not from a side by side field comparison of these two products.
The exit pupil difference, exactly
The working
Exit pupil = objective diameter / magnification. 8x42: 42 / 8 = 5.25 mm. 10x42: 42 / 10 = 4.2 mm.
Both figures are exact arithmetic from the published objective diameter and magnification of each configuration.
A larger exit pupil means more of the light your eye can actually use is being delivered, which matters most in dim conditions such as dawn, dusk or deep shade under a canopy.
An 8x42 binocular gives a 5.25mm exit pupil against 4.2mm for a 10x42, both from the identical 42mm objective lens.
Sourced figure
| Configuration | Objective | Magnification | Exit pupil |
|---|---|---|---|
| 8x42 | 42 mm | 8x | 5.25 mm |
| 10x42 | 42 mm | 10x | 4.2 mm |
A typical dark-adapted human pupil dilates to roughly 4 to 7 mm depending on age and lighting, a convention rather than a published constant, which is why an exit pupil below about 4mm starts to feel dim to some users in low light.
Why 8x is noticeably steadier to hold
Magnification does not only enlarge the target, it enlarges every bit of hand tremor between your grip and the image, in direct proportion to the magnification itself. A 10x binocular amplifies that tremor 25 percent more than an 8x binocular does, which shows up as a visibly less stable image at the eyepiece, particularly after your arms have tired from holding the binocular up for a while. This is not a subtle effect: most users can feel the difference in steadiness between 8x and 10x within the first few seconds of comparing them side by side.
What 10x actually buys you
More reach, plainly. A 10x binocular resolves finer detail at a given distance than an 8x binocular does, which matters for open country glassing where subjects are routinely far enough away that the extra magnification reveals detail an 8x simply cannot. The tradeoff is real: a dimmer image in poor light and a shakier view that can partly offset the resolution gain, especially without a tripod or a solid rest to steady the higher magnification.
So which should you actually buy?
8x42 is the better all-around choice for most people: brighter in poor light, steadier to hold for a long glassing session, and close enough in reach to 10x that the difference rarely decides whether you find or miss game or a target. 10x42 earns its place for open country hunting or long distance observation where the extra magnification's resolution gain outweighs the dimmer, shakier image, particularly for a user who braces the binocular against something solid rather than holding it entirely freehand.
Sources
- Vortex Optics published specifications
- Exit pupil, objective diameter divided by magnification, standard published optical formula
- Typical dark-adapted human pupil diameter, standard published convention
Frequently asked questions
Is 8x42 or 10x42 better for hunting?
8x42 for most hunters, because its 5.25mm exit pupil gives a brighter image at dawn and dusk, and it is noticeably steadier to hold over a long glassing session. 10x42 suits open country hunting where subjects are consistently far enough away that the extra magnification's resolution gain outweighs the dimmer, shakier image.
What is the exit pupil difference between 8x42 and 10x42?
An 8x42 gives a 5.25mm exit pupil, from 42 divided by 8. A 10x42 gives 4.2mm, from 42 divided by 10. Both share the same 42mm objective, so the entire difference in brightness comes from the magnification alone. The larger exit pupil on the 8x42 delivers more usable light to the eye, particularly in low light.
Why does 10x42 shake more than 8x42?
Because magnification enlarges hand tremor in direct proportion to the magnification itself, so a 10x binocular shows 25 percent more apparent shake than an 8x binocular for the identical amount of hand movement. This is a fixed optical consequence of magnification, not a difference in build quality between comparable binoculars.
Do I need 10x binoculars for long range shooting?
Not specifically. Binoculars are for finding a target or game, not for the fine detail work a spotting scope handles once something is located. 10x binoculars offer somewhat more reach for that finding job at long distances, but the brighter, steadier 8x42 is the better all-around tool for most shooters, with a spotting scope covering true long range detail.
Is a bigger exit pupil always better?
Only up to the point your pupil can actually use it. A typical dark-adapted eye dilates to roughly 4 to 7 mm, so an exit pupil larger than your own pupil at the time delivers light that never reaches your retina. In bright daylight your pupil may be closer to 2 or 3mm, making the 8x42 and 10x42 difference far less noticeable than at dusk.
Can I use 8x42 binoculars for birding as well as hunting?
Yes. 8x42 is a common general-purpose choice across birding, hunting and casual observation, because its brighter image and steadier hold suit long observation sessions in a range of light conditions. Serious birders sometimes prefer higher magnification for distant identification, but 8x42 remains a widely recommended starting configuration for most users.
Researched, not professional advice. This page is compiled from published manufacturer specifications, published optical and ballistic formulas, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are shooter convention rather than sourced numbers, and they are labelled that way wherever they appear. Ballistic figures come from a point mass model using the ballistic coefficient the maker publishes, so treat them as a starting point and confirm them on paper at a measured distance. Confirm your firearm is unloaded with the action open before you mount, level, torque or bore sight anything. Verify a zero only on a supervised range or a safe, legal backstop, know what lies beyond your target, and follow the law where you hunt and shoot, including rules on land access and permitted cartridges.