mercoledì 19 settembre 2012

Stampate i vostri targets

Grazie a Kleanthes Koniaris ognuno può stamparsi "in casa" i propri targets per allenarsi.

Everybody likes free archery targets that can be printed on a nearby color printer. The novel thing about my free targets is that they contain an overlay of grid lines spaced by 1moa. These targets can only be used correctly at their rated distance, but provide a very powerful tool for the analysis of groups of arrows.
The "minute of angle" spacing is very important, because it (a) provides a very natural way to view group sizes at various distances, (b) makes sight adjustment very natural (as sights ultimately deliver some amount of moa/click), and (c) provides simple notation for recording arrow impacts.

As you probably know, a circle is divided into 360 degrees. A 70m Olympic target from the shooting line is one degree wide! So, if you want to talk about the width of (say) the ten ring, you need something smaller than a degree. While it makes perfect sense to use fractions, like 0.1 degree, there is a long-standing solution, the "minute of angle." Just like an hour is split up into sixty minutes, a degree is split up into sixty "minutes of angle." (I know it is confusing to use the word "minutes" for two unrelated concepts, but that's what's done.) So, a 70m archery target is 60moa wide. (The alternative choice in angle is the milliradian, but I think that it's a little too wide to be convenient for our purposes.)
To give you an idea, a person with 20/20 vision can read a letter that is about 5moa wide, and perhaps see a line that is 1moa wide. A fine rifle can shoot groups under 1 moa.
If we place the official FITA targets at their official distances, and stand at the shooting line, their widths are as follows:
A large target is easy to hit, and the best way to think about the width of the target is in moa. So, one can see that 90m is tough, not only because of the wind blowing arrows around, but the size is only 47moa! So, you can see that 30m is the easiest, for example, as the target is very wide (92moa), and there is not a lot of chance for the wind to blow arrows.
Not only does it make sense to think of the width of your target in moa, the same holds for the width of your groups. The main idea is that your group size should be roughly the same size in moa, no matter the distance, until air effects come into play (this will spread your groups out and make them wider).
If you print a target, be sure not to fit it to a page (or zoom), as the printed size will be wrong. Do compare your target to an official FITA target to be sure that nothing went wrong. If you observe some problem, email me, and perhaps I can fix it or help....
For those of you in the United States or Canada who have never been blessed with ISO paper, the sizes are quite clever, and worth using; A4 paper fits in most US Letter printers, in passing, so there is no excuse not to use it!
For those who want a peek at my PostScript program that's still under development, (I'm amused with the procedure "ldict," in passing; it's nearly a PostScript macro.) I expect to improve the targets shortly, so do come back....
Kleanthes Koniaris, email.