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Home Fly Fishing Techniques The Importance of Precision


The Importance of Precision Casting

 A Trout's Cone of Visiion

A Trout's Cone of Vision



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     When fly fishing small streams, precision casting is of paramount importance and thus, it is extremely important that you learn to land you fly on a coffee saucer at thirty feet because, if you are out of the trout's chosen feeding lane by even a few inches, then you fly will often be refused or ignored if it is seen at all. Consequently, it is very important to understand how a trout sees its world from its own unique point of view so that you can also understand how they view your flies.


     Therefore, in order to explain this, we need to dabble with a little math so that we can examine the fish's cone of vision. First, there is a law of physics called Snell's Law that states: "The angle of incidence equals the angle of refraction". Thus, light that strikes the surface of water at an angle less than 48.5 degrees is reflected and light that strikes the surface of water at an angle greater than 48.5 degrees enters the water. Now, what that really means is that when a fish is lying under the water and it looks up, the under-surface of the water looks like a big mirror that reflects a picture of the streambed. However, that mirror has a large circular hole in the middle of it directly above the fish’s eyes that allows the fish to see the surrounding surface environment. Also, the diameter of the fish's window is approximately three times the water’s depth so always keep it in mind that, “if you can see the fish, then the fish can see you!”


     However, a fish’s eyesight also has a fatal flaw that any good fly fisherman would be a fool not to take advantage of. Just because a fish can see what is above it clearly, we tend to assume that they can also see what is in front of or beside them clearly. But, this is not true. Due to some quirk in the shape and construction of a trout’s eye, things that float past them at eye level in the water column appear slightly blurry. Thus, fish depend on the color, general outline, and an appearance of movement to indicate that an object is alive and thus might be good to eat.


     Therefore, as you can see, if a trout is holding in relatively shallow water, then the size of his cone of vision is comparatively small and thus, being able to land your dry fly precisely within the trout's feeding lane is paramount to getting your fly seen by the trout. Also, landing you nymph or streamer in the exact spot it needs to be in is also very important because a trout often will not leave the comfort zone of his established feeding lane even to snatch sub-surface menu item. Thus, precision fly casting is of paramount importance to catching trout on small streams regardless of whether you are fishing above or below the surface!





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