Why do my front sight look sharper with narrow gaps?

[fkw]

I don't know if my eyes are seeing this correctly.

As I narrow the rear sight width down to a slit against the front sight, the image of front sight becomes sharper.

Am I seeing this correctly? Is there a scientific explanation for this? Or am I just imagining this sharper front sight?

[orionshooter]

Could it be that by making the front sight more difficult to see (by narrowing the rear gap) you are forcing yourself to focus much harder on the front sight??

[Spencer]

...Am I seeing this correctly?

- Yes, and no. If the front sight is sharpening up it might be that your natural focal length is not at the front sight distance.

...Is there a scientific explanation for this?

- Yes - the rear sight is working as a (partial) aperture

...Or am I just imagining this sharper front sight?

- No

Is there an advantage in using this effect?
- unless you have a hold that approaches the steadiness of a machine rest, NO.

[David M]

Also, see what it looks like after an hour or so of shooting, chances are that your eye will give up, be watery, very sore and blurry.