I’m off to Denver tomorrow to speak at The Fly fishing Show held at the Merchandise Mart in Denver. It’s always a fun time, but this year it will be tinted with the sadness of the death of my long-time friend, Charlie Meyers. He was the Outdoor Editor of the Denver Post and was a dedicated conservationist that was not afraid to write what he felt to be true and just, regardless of the toes that he stepped on. Good bye, old friend, I will remember our discussions, tiger fish, and sand grouse.

The diameter of the fish’s window is fixed by the physics of refraction. If the apical angle of the window were 90 degrees, then the diameter of the window would be exactly twice the depth of the fish. Since it is 97 degrees, the diameter of the window is 2.26 times the depth of the fish, in theory. In practice, it is much closer to the simple 2X the depth. This is because the images of objects above the surface and under 10 degrees above the horizontal are so very strongly compressed as the light bends sharply over the edge of the window that these objects basically become part of the window’s edge–like a border on the window. This border effectively closes the clean, crisp, see-though portion of the window a bit. So if one simply figures that the diameter of the window is about twice the depth, that’s good enough for angling purposes.

Now note carefully, I said the diameter of the window. The front edge of the window, therefore will be the distance of the window’s radius from the fish. If the fish is down two feet, the front edge of the window is two feet upstream from the fish. There that’s easy. More on estimating fish depth in a future post.

Mike Allen casting from a rock on the Siberian River in NZ. NOTE: mountains, rocks in background.

Mike from under water. Where in the heck are the mountains and rocks? They are folded into the edge of the window. Look carefully, you will see them.

The diameter of the fish’s window is about 2X the depth of the fish. As the fish changes depth, the size of the window changes proportionally.

Refraction is the bending of light as it passes from a medium of one optical density into a medium of a different optical density, as from air to water or water into air. The amount of bending is dependent upon the incident angle of the light.  In the diagram below, a light ray, “A” strikes the water at right angles and passes through the surface without bending. But as the incident angle decreases (becomes less than 90 degrees) the light bends more and more–rays “B” and “C.” Light striking the surface parallel to the surface, bends downward 41 1/2 degrees (dotted lines). NOTE: light passing from the water into air will bend exactly the opposite of light passing from air into water.

Since light is coming into the water from all directions, refraction creates a cone of light with its base on the surface and its apex at the fish’s eye. The apical angle of the cone is 97 degrees. The base of the cone is a circular opening at the surface through which the fish sees the entire outside world. This opening is called the “Fish’s Window,” and was first described in 1621 by Willebrord Snell van Royen. Only the light passing through the window enters the fish’s eye. Notice line “D,” It’s a ray entering the water beyond the window; refraction bends it such that it cannot reach the fish’s eye. There are a number of somewhat startling ramifications to the window relative to the fish’s vision, and to the angler’s perspective of the fish. We will take these up in future posts. Watch for them.

Refraction of light between air and water. See text for explanation.

Many anglers don’t realize that water absorbs light wavelengths differentially. That is to say, red light is absorbed differently that blue or green or yellow or orange. On top of that, different waters will absorb light differently. Here’s a chart from my book, “Presentation,” showing this differential absorption of different waters. What this means is that red flies are basically gray to black below about 6 feet. Other colors drop out at different depths in clean water, water with algae, and bog water. However, what the chart doesn’t show, and can’t really, is the fact that fluorescent colors are good at all depths. A substance fluoresces when it absorbs light at one wavelength and emits it at another. So fluorescent red will absorb any other color and emit it as red. For flies to be fished deep, fluorescent colors will hold their colors, other turn black—do you suppose this might be the secret of the black leech? It is black no matter at what depth it’s fished, and black is a strong silhouette color.

Background space light is the color of the water as it appears from underwater looking horizontally. In clear waters, it is blue; in algae filled waters, its yellow green; in a bog, it reddish brown.

Hey! Want a really great T like the one I’m wearing? Well, get on over to Fish, Flies & Water (Jason’ Blog) and order one today. This cotton poly blend feels like silk. I know fish will like me bettter now that I’m wearing this–I’m not promising that you’ll catch more fish, but you certainly will look smart trying! There’s 100% cotton Coastal Green in Unisex and Horizon Blue in Women’s sizes, too.

GB in JB T. Get yours today!

Sounds a bit like an oxymoron, but it’s so easy and so fast to tie, that even oxen can do it. The nail knot has been around for a long, long time, and it’s a really great way to attach the leader to the fly line. I actually attach a 12—15 inch piece of leader butt to the fly line to make a connector, and then loop my leaders on and off the connector. Go to Jason’s Blog to see the connector concept and the Perfection Loop that we use to make the leader to connector attachment.

To make a nail knot really fast without a nail or tube, follow the diagrams below. I developed the “twist” technique for this knot many years ago, and everyone that tries it can do it, and do it fast.

Step 1. Make a loop in the leader material, then wind the short end of the leader around the fly line and through the loop. Wind the short end up the fly line. Drawing by Jason Borger

Steps 2 & 3. Simultaneously pull and twist ONLY the short end of the leader to spin the knot over. Don't over tighten. Slide the mono coils down toward the end of the line, push them together while gently drawing out the extra mono, then tighten firmly (really firmly) and clip off the ends. Drawing by Jason Borger

Notice that the leader comes off the side of the line when the knot is done. Sometimes the end of the line will catch in a guide, so I make a slight variation on the knot that prevents hangups. It’s called the Needle Knot and is very easy to do. Follow the diagrams below.

Step 1. Insert a needle into the end of the fly line about 1/8 to 3/16 of an inch, and then out the side. Allow the needle to remain in place for a couple of minutes so the plastic of the line will stretch a bit. Drawing by Jason Borger

Step 2. Trim the end of the mono to a point, pull the needle out, and thread the mono in the end of the fly line and out the side. Now tie a Nailess Nail Knot. Notice that the leader now comes right out of the center of the fly line. This connection will flow through the guides very smoothly. Drawing by Jason Borger

The construction of fly lines took a huge leap forward when shortly after the second world war, manufacturers began to build lines with a level braided nylon core coated with plastic. The taper in the line is built into the coating, not into the core. With this technique, lines could be made that floated better than silk and others that sank better than silk. Floating lines were made by adding microspheres of glass filled with air to the plastic coating. To make the lines sink, the manufacturers replaced the air filled microspheres with powdered lead. For the sinking lines, manufacturers also started using a braided Dacron core rather than nylon.

Since the early days of building plastic coated lines, there have been improvements in the microspheres, other materials besides lead are widely used in sinking lines. tapers have improved, coating additives have changed, and so on, but the basic structure is still the same.

When manufacturers switched to the new methodology of making lines, they very quickly discovered that the old letter designation system (see the last post) was no longer adequate. The reason is very simple. A floating fly line of “D” diameter (.045″) was much lighter than a silk line of the same diameter, while a sinking line of the same size was much heavier than the silk line. And, since a fly rod is desigtned to cast a specific line weight, a “D” floating line was too light for a rod designed for “D” silk, and the “D” sinking line was way to heavy.

Manufacturers quickly gave up the diameter designation in favor of a strictly weight-based system. The plastic-coated line designation is now a number category, 1—15. Each number indicates a specific line weight. So, a number 5 floating line weighs exactly the same as a number 5 sinking line, even though the floating line is significantly larger in diameter. Furthermore, every 5 weight line, regardless of the taper style is the same weight. All these lines weigh the same: WF5F, WF5S, WF5I, WF5F/S, L5F, L5S, L5I, L5F/S, DT5F, DT5S, DT5I, DT5 F/S, SH5F, SH5S, SH5I, etc. A 5 is a 5 is a 5. A 5 by any other name is still a 5. That’s the beauty of the system. If one owns a 5-weight rod, that it will properly handle any 5-weight line, regardless of taper or density.

Line weight is the actual weight of the first 30 feet of line in grains (7000 grains per pound; 437 1/2 grains per ounce). Manufacturers often add a short tip (6 -12 inches) of level line at the very front of the taper on WF and DT lines. The weight of this section is excluded. Here are the categories:

Weight    Actual Line   Allowable
Class      Weight (gr.)   Variation (gr. +)
1                  60                         6
2                  80                         6
3                  100                       6
4                  120                       6
5                  140                       6
6                  160                       8
7                  185                       8
8                  210                       8
9                  240                      10
10                280                      10
11                330                       12
12                380                       12
13                450                       15
14                500                       20
15                560                       20

When I started fly fishing in 1955, fly lines were designated with a lettering system, beginning at A and running through I. The letter designation specified a diameter, with “A” being the largest diameter and “I” the smallest. This brought line designations up to par with leader “X” designations, each “X” representing a diameter (for example, 3X = .008,” 7X = .004″). The diameter designations were OK in silk because every line was made of the same material and therefore weight designations were not important.

But, when plastic lines became available, the letter designation (a shorthand way of indicating diameter), was no longer sufficient. A size “D” floating line weighed considerably less than a size “D” fast sinking line. And since it is the weight of  the line that we cast and not its diameter, using diameter alone as the indicator of line size was no longer acceptable. Thus came the American Fishing Tackle Manufacturers Association (AFTMA) weight categories, designated with numbers 1 through 15. We’ll look at these in another post.

So, relatively early in my fly fishing career, manufacturers switched horses in the middle of the stream and began using the AFTMA numbering system. It was a great improvement, really,, and allowed some real refinements in tackle and tackle designations.

Here’s a chart that shows the old system of letter designation versus the new AFTMA system. The comparisons are for silk against a floating plastic line.

ALPHA   DIAMETER           DT          WF        AFTMA
#              IN INCHES        LINES    LINES         #

I                 .022                                                  1
H               .025                                                   2
G               .030                   IFI           IFG          3
F                .035                 HFH        HFG          4
E                .040                HEH         HEG          5
D                .045                HDH        HDG          6
C                .050                HCH        HCF           7
B                .055                GBG         GBF          8
A                .060                GAG         GAF          9
2A              .066                G2AG      G2AF        10
3A              .070                G3AG      G3AF        11
4A              .073                G4AG       G4AF       12

I occasionally get questions on old line designations, so in this post I want to discuss the old, old system of line sizing. Originally, silk lines were not designed by the weight standards that are in play today. Rather they were designated by a simple numbering system, 1, 2, 3, etc. Later the numbering system was converted to an alpha system in which the line diameter was designated with a letter, for example HDH (a double taper of about 6 weight).

Kingfisher was a producer of lines for many years, and one can find  their silk lines yet today. The Phoenix line  (Silk Lines), currently manufactured today, is built on the Kingfisher tradition. The new lines are all categorized by weight, like all other modern lines. But in the original system a Kingfisher line number 1 is the same as an AFTMA 3 and the Kingfisher 7 is the same as an AFTMA 12. The AFTMA scale, as you know, is sliding, but we don’t know what the Kingfisher scale was. However, if we assume that the Kingfisher lines 1 through 7 were evenly spaced in terms of weight (most likely the case), then their number 1 would be 100 grains and their number 7 would be 380 grains. Therefore each line would be 46.67 grains heavier than the previous line (380-100/6 = 46.67). So, the lines would go like this:

Kingfisher #/wt    AFTMA Equivalent
1–100 g.                       3–100g +/-6g
2–146.67g                    5–140g +/-6g
3–193.34g                    7–185g +/-8g
4–240.01g                   9–240g +/-10g
5–286.68g                  10–280g +/-10g
6–333.35g                   11–330g +/-12g
7–380.02g                  12–380g +/-12g

Extending the edges of the fish’s binocular zone rearward defines the limits of its field of vision, or so theory says. The theory, furthermore, promotes the idea that the limits of the fish’s peripheral vision clearly establishes a 30 degree blind spot to the fish’s rear. Therefore, the theory continues, one can sneak up on fish from the rear, and they’ll never see you. Only problem is, this is theory, not reality, and it doesn’t consider all the ramifications of the fish’s ability to see the angler.

First, the fish’s eyes bulge a bit, and they can actually see further to the rear than simple line drawings would indicate. Second, the fish can rotate its eyes rearward,  enhancing its rearward view. Third, the fish’s swimming movements wiggle its head side to side slightly, constantly shifting whatever blind zone really exists. But far more important, the part of the angler that spooks the fish is the part above water, and the rearward blind zone doesn’t exist when the fish is looking up at its window.

The reason that anglers can “sneak up” on fish from the rear is because fish are normally looking upstream for food, and their attention is thus aimed upstream. It’s really not hard to “sneak down” on a fish, either, if one moves slowly, wears “environmentally friendly”  clothes (read, colored like the stream side vegetation), and keeps the casting to a minimum. I’ve done it hundreds of times on smooth waters like Henry’s Fork, Silver Creek, the Test and Itchen, New Zealand’s crystalline waters, and many other similar waters.

The fish’s eyes are especially sensitive to contrast and motion, and doing anything that exposes you to that sensitivity is a sure-fire way to spook the trout. Be the predator that you have to be.

The rear blind spot is 30 degrees in theory, far less in actuality, and non-existent when the fish is looking at the surface.