A quick look through Lancaster Archery Supply’s lineup of
3-D and target scope offerings for compound bows shows scopes measuring 29, 30,
35, 39 and 41 mm, among some other sizes.

Recognizing there are different sizes of scope housings available begs the obvious question, “Which size is right for me?”

And the answer is, “That depends on what you want to see.”

Scopes and lenses are married to provide a certain view of
the target. Some archers like to really zero in on the arrow’s exact point of
impact, while others prefer a more distant view, so they can relax while
aiming.

The smaller the scope housing, the smaller your field of
view. That field shrinks even further the more you magnify it with a lens.

So let’s say you are shooting at a typical Vegas 3-spot target face for an 18-meter, indoor shoot. A small scope housing will enable you to really focus on each individual spot, while minimizing your view of everything surrounding each spot.

X-Spot 29mm scope

Some archers find it distracting to see much surrounding the
intended aiming point. So maybe you start with a 29mm scope housing and then
choose a magnifying lens that blows up the target enough to all but completely
fill your view of it through the scope when you’re at full draw.

On the other hand, some archers feel “claustrophobic” when they can’t see anything but the target face in their scope. They like a little extra room around the bull’s-eye, which allows them to settle down and hold the bow steadier. So maybe a 35mm scope is a better choice for that archer.

Bowfinger 20/20 35mm scope

Moving outdoors, you’ll have to address the same issues for
field archery, 50-meter rounds and other bull’s-eye target rounds. How much
area around the target do you want to see? Find a scope and magnifying lens to
create that view.

For 3-D, the larger scopes dominate because most archers want to see the whole target in the scope. And those targets might range from a tiny skunk to a life-size bull elk. Being able to see the whole target allows you to find reference spots to aim when scoring rings are not readily visible. Also, for those archers who shoot unknown distance, seeing the whole target allows them to better judge the distance to it. As a result, many archers choose the 40- and 41-mm scopes for their 3-D setups.

Shrewd Nomad 42mm scope

Lighting is another factor to consider for an outdoor scope.
The smaller the scope, the less light will get through it to your eye. In an
open field, that’s probably not a problem. But if you’re going to be shooting
in the woods with a dense canopy, then going with a bigger scope to allow more
light in might be the best choice.