I built this simple fully-adjustable bow sight out of scrap wood and plastic I had at home. You can have as many sight points ("pins") as you like, and they can be very close together. The sight is frameless and does not cover up any part of the animal or target.

The sight is very simple, and hardly needs instructions once it's described: It's just a rectangle of acrylic mounted in front of the riser, and the sight points are marked with a fine-tip wet- or dry-erase marker. Took a lot longer to write up the instructable than to make it.

You can color-code for different users of the bow or for different arrows or for field points vs. broadheads. You can put in sight points for all the targets in your club's field course, and even use one side of the acrylic for your permanent default sight points and the other side of the acrylic for wind-adjusted sight points. You can write distances and other notes beside your sight points. And all this at little to no cost depending on what you have in your scrap box.

NOTE: There is at least one potential safety issue, which is that perhaps if an arrow jumps or shatters and hits the sight it might ricochet at you. Don't use crooked arrows and always test carbon arrows before use. USE THE SIGHT AT YOUR OWN RISK. If this is a worry to you, don't use the sight, or maybe use undercut plastic screws or a weak glue (e.g., hot melt) to attach the plastic sight to the plywood mount for a more controlled failure.

I designed the sight for a recurve (a 66" Samick Polaris, 26# @28"), but it might work for a compound, perhaps with some changes. I'd love to hear if you got this working on a compound.

Parts:

Piece of clear see-through plastic that's rigid enough not to bend noticeably in the wind when supported by one side and clear enough that you can easily see what you're shooting at through it. I used 1/16" acrylic from some old Melissa and Doug toy boxes. The exact dimensions depend on how much adjustment range you need for your bow. My final sight is about 3.7 in x 2.6 in. If you can't find any acrylic sheet you want to sacrifice, you can order acrylic or polycarbonate sheet from Amazon.
Piece of 3/8" - 3/4" plywood, big enough to cut about a 2 in x 4 in rectangle. Better quality plywood will reduce warping and thus reduce the need to re-adjust the sight. I used scrap 1/2" Baltic/Russian birch.
Either: Two #10-24 screws long enough to go through the plywood and anchor to the sight threads on the bow. (If you don't have sight threads on the bow, you'll need to put in a threaded insert, or just use wood screws to mount directly to the riser.) The screws I had were too long and I had to trim them.
Or instead for greater safety: Hot-melt or other weak glue for semi-permanent attachment of plastic to wood.
Two small wood screws
Fine-tip dry- or wet-erase marker. (Fine-tip dry-erase markers with a built-in eraser might be the best.)
Kleenex or paper towel
Optional: Different colored of markers for multiple users
Optional: Stickers instead of markers.
Optional: Wood finish, paint, camo fabric, etc.
Optional: Washers for the wood screws
Optional (if you want to get a better idea of placement and size): Toothpicks or wooden matches, masking tape and target.

Tools:

Safety goggles
Metal ruler
Box cutters
Saw
Drill
Sand paper / flat file / sander

Step 1: Figure Out Size of the Sight's Window

You have two options.

Option 1: Decide to make the sight window really big, but not so big it will get in the way of arrows and other equipment, and later cut it down to size once you've started using and found how much of the sight area you need.

Option 2: Put masking tape on the inner side of the riser and sight along the edge of the masking tape to see how high up and how low down the marks for your closest and furthest expected shooting distances should be. Tape up match sticks to sight along the ends of to see how far away from your riser (left of riser for a right-handed bow) the sight's window should go, as well as how high up it should go. Add a good safety margin to take into account variation of conditions (arrows, points, wind, and maybe multiple users), plus about 20% to account for the fact that the sight is further away from the eye than the riser. You can always trim the window down later. Then add to the width the thickness of the plywood you will mount it on, plus the thickness of the bow from the sight mounting holes to the edge of the riser where you had the masking tape.

Whichever option you went for, you can now mark with masking tape how far up and down along the riser you want the sight's window to go. Keep it out of the way of the arrows!

Step 2: Cut Out the Window

Take some 1/16" (approximately) clear plastic, and cut out a rectangle of the right size (see previous step). I cut the rectangle by scoring several times along a metal ruler with box cutters, and then just snapping along the line (safety goggles!). The first line will probably need to go all the way across the plastic piece to snap nicely.

Clean up the cut edges and round off the corners with sand paper, flat file or sander. (I used a rotary tool with a sanding drum attachment.) Since you may want to trim more later, don't put too much time into this.

Step 3: Plywood Mount

Make a rectangle of plywood wide enough so you can screw it to the sight mounting holes on the bow (they were 1.3 inches apart for me, and I went for 1.9 inches width) and long enough to put the sight window at a decent distance in front of the riser. I went for about 4 inches.

Drill holes for the #10-24 screws on the side of one end of the mount at the right distance apart for the sight mounting holes on the bow. Check that you can attach the mount to the riser. If you weren't precise enough in drilling the holes in the mount, just enlarge the holes a little.

(If your bow doesn't have sight mounting holes, you might want to carefully drill into the riser and attach the sight with wood screws. If the sight is light enough, strong double-sided tape might do the job, too.)

Optional: Finish the wood on the mount (important if you're going to be using it in bad weather) or paint or put camo on it.

Step 4: Attaching Sight Window to the Mount

Attach the sight window to the forward edge of the mount in such a way that it will be in the right place vertically along the riser (see the measuring step).

I attached the window with two wood screws (pre-drilling both the wood and the plastic) and washers.

A safer method with respect to ricochet issues would be to attach with a weak glue, like small dots of hot melt glue, so that an errant arrow or arrow piece will likely knock the window off the mount.

Step 5: Using Sight

To adjust for a particular target distance, make a temporary dot on one side of the sight with the marker. Align that dot with some point on the target in such a way that if you aim along that dot your arrows consistently hit one place on the target. (If your initial dot didn't let you hit the butte at all, just move the dot.) If like me you're too much of a beginner to get much consistency, this can be pretty rough--you can fine-adjust later as your skills improve--but just see roughly where your arrows group. Then look through your sight with bow in shooting position, aligning the temporary dot at the place you were aiming at, and make a new dot in the center of where your arrows were grouping. Erase the temporary dot. You might want to put the temporary dot on the opposite side of the plastic from where the final dot will be, so you don't accidentally erase the final dot.

Repeat for other target distances. Once you have two distances, you can extrapolate where the next dot can be placed, and you may be only making small adjustments.

Instead of dots, you can draw little crosses or circles or arrows.

You can use stickers instead of marker dots if you like, e.g., three-ring binder hole reinforcers, little arrows cut out from some sticker, etc. Maybe cut out a part of a glow in the dark sticker even.

You can also use a permanent marker for really permanent dots. Or glow in the dark paint.

If you eventually find out you don't need as big a window on the sight as you initially put in, you can trim it down. Or if you find that you can't reach some target with the window, just cut a new one.

Step 6: Tweaks

Some time after writing the Instructable, I decided to reduce weight and wind profile, plus make it look better to my eyes, by drilling two lightening holes.

Also, I wanted to be able to easily take it off and put it back on, so I made some wooden knobs for the attachment screws. Basically, I made wooden squares with countersunk holes, and superglued the screws inside. I added washers on the bottoms, and superglue-treated the whole knob.