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G'day Mok!
Yes, older binos can be difficult to collimate, sometime impossible by most untrained people.
If the binos need to be disassembled to collimate, it is a time consuming job.
But, some older binos, and most newer porro prism types, have one or two pairs of adjustment screws on the prism body. Sometimes you need to peel back the plastic or rubber grip that covers the body. The following info is for this type of binos. The other type that requires the binos to be disassembled, it is very involved. I can't remember where I saw an article on adjusting these. Maybe someone else has a link they can share.
If your binos are this 'external screw' type, these are very easy to collimate. You do it on a clear night when you have bright stars to easily find as you will be frequently going from a brightly lit room to under the stars to check on your progress.
Most rubber grips over binos are just lightly glued on along the rim/edge of the grip. This next part can be dangerous - you need to know how to handle a knife to do this safely, or you stand a real chance you will slice yourself open! A very sharp Stanley knife is essential here to not damage the grip and the binos. Start along the top of the body, and slowly cut away the grip, lifting it slowly a bit at a time to see where the glue is. You don't need to peel away the whole thing, just enough to access the screws. There might be just the one pair (one on each body like on my set pictured below), or two pairs, sometime even three.
Mark one side of the screw head and the body with a little line to indicate the starting point of your adjustments. You need this reference mark to keep track of which way you are turning the screws. These little screws might be the slotted head type, Phillips head or Allen key type. They will also be semi-glued in place with something like Loktyte just to hold them in place. A sharp, firm twist of the screwdriver will release them.
Before you begin adjusting, go outside and check the image to see how divergent the images are. Now back inside, and working with only 1/8th turns, turn one screw clockwise and the other counterclockwise. Go back outside and check your progress. If the images are closer to a single one, keep going this way. If the images are wider apart, turn each screw the other way. Easy.
Always take your time with this. Don't try to go more than 1/8th turns - you will get a lot of shift in the image this way and it is easier to control.
When finished, unless you have the appropriate bog to semi-fix the screws in place, leave them be. Yeah they are more likely to shift, but now it is easier for you to readjust them.
The rubber grip, using something like a silicone, and using very little, replace the grip, putting the glue where it was originally. Just enough is better than too much incase you need to make an adjustment later on.
In the picture below, you will see where I had made my reference mark on the bino body, and where the screwhead is now after the adjustment was made.
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