Optics fail quietly. A binocular that has drifted out of collimation does not look broken, it just gives you a headache after twenty minutes and you blame the weather. Twenty minutes in September is worth more than discovering any of this in October.
The eight checks
What you need
- Your binoculars, rangefinder and tripod
- A distant straight vertical line - a power pole, a building edge
- Fresh batteries
- Lens wipes made for coated optics
- 1
Check collimation on a distant vertical line
This is the one nobody does. Find a distant vertical line - a power pole, the corner of a building. Look at it through the binoculars and let your eyes relax, then slowly pull the binoculars away from your face by an inch. If the two images separate into two poles that do not merge comfortably, the barrels are out of alignment. That is what causes unexplained eye strain and headaches, and it is a warranty job rather than a field fix.
- 2
Set and lock the diopter
Cover the right objective, focus on a distant object with the center wheel using only your left eye. Then cover the left objective and adjust the diopter ring only until the same object is sharp to your right eye. If your binocular has a locking diopter, lock it. A drifted diopter is the second most common cause of a binocular that 'went soft'.
- 3
Check the focus wheel through its full travel
Run it from close focus to infinity and back. It should be smooth with no gritty spots. Grit in the mechanism is what eventually makes a focus wheel stiff in cold weather, and blowing it out now is easier than living with it in November.
- 4
Test the eyecups
Twist them up and down several times. They should hold position. Eyecups that creep down under light pressure will cost you the full field of view at the worst moment, and if you wear glasses they need to stay fully down.
- 5
Clean the lenses properly, once
Blow the grit off first, then brush, then use a wipe made for coated optics in a light spiral from the center out. Never wipe dry. The full method.
- 6
Put fresh batteries in the rangefinder and range something known
Fresh CR2 or whatever it takes, then range an object you know the distance to - a fence line, a tree you have paced off. Confirm it reads correctly in both the uncorrected and the angle-compensated modes, and check which mode it is left in. A unit sitting in LOS mode all season gives you the wrong number every time.
- 7
Set the rangefinder's ballistic group, if it has one
If your unit uses TBR/W or a similar ballistic output, confirm the selected group matches what you are shooting this season. If you changed loads or rifles, this is probably wrong. What TBR/W does.
- 8
Check the tripod and adapter
Run the leg locks, check the head is tight, and mount the binocular to confirm the adapter still holds its level after five minutes. If it rotates, you need a clamping adapter rather than more torque. Adapters.
Two things worth fixing now
If you are still using a neck strap, a harness is $29 and it is the cheapest meaningful upgrade available. The binocular stops swinging, stops getting rained on, and stops ending up in your pack. Harness picks.
If the collimation test failed, send the binocular in now. Every serious manufacturer will realign it, Vortex's VIP warranty covers it unconditionally, and turnaround in September is much faster than in October.
Questions people actually ask
How do I check if my binoculars are out of alignment?
How do I set the diopter on binoculars?
Why do my binoculars give me a headache?
Read next
No product picks: this is a maintenance checklist, and the honest conclusion of most of it is that your existing gear is fine. The two items it does recommend - lens wipes and a harness - are linked in context.