Difficulty tying your fly to the tippet? Try this!
As you get older and the light gets dimmer, it becomes increasingly difficult when fishing to thread the fly, let alone knot it onto the tippet. An obvious answer to this problem is to carry some sort of magnifying optics with you to facilitate the process. Often in low light conditions even that is not enough. If you pull out a flashlight, you can sometimes see well enough to tie on the fly, but then you've just lost your night vision at the time when you needed it the most. And, of course, the trout become very active right around dusk. Why is this happening?
The ability for the human eye to discern small details and pick them out of a background typically decreases with age. Part of the problem is the change in the physical shape of the eye as we get older which usually causes us to lose the ability to focus on items up close. Another part of the equation has to do with chromatic aberration in the human eye. Different colors have different wavelengths and the human eye focuses differently for each of them. When you get too many different colors all in the same area, it becomes difficult to pick the detail out of any of it. Without getting too far into specifics, suffice it to say that it is easier to pick out detail against a solid mono-colored background than a mottled or multi-colored one.
So, next time you're on the water with the light failing, the fish rising, and having trouble tying on the fly, try holding the fly up against a single-colored background - preferably a light, single-colored background. A good candidate for this is the sky overhead. It is one of the last things to go dark if it is not a terribly cloudy day. Even if it is cloudy, you can usually find a cloud big enough to use as a solid color. Sometimes the solid glare from the low light on the water does the trick. Look around. It might be that the large elephant-eared leaf of a wild rhubarb does the trick. Using any of these backgrounds makes it much easier than trying to see and tie on a fly against the multi-colored, multi-edged background of streamside vegetation. This is not a cure-all, but it helps and it sure beats not fly fishing!