Explanation of Co-Witness

[Jay Cunningham]

An absolute co-witness means that when you look through your iron sights and optic your front sight post appears dead center in your optic with the red dot on the tip.

A lower third (sometimes called a SOCOM) co-witness does the same as above except in the lower third of the optic. You can slightly raise your head position and just view the dot.

[Buckaroo]

To add just a bit of clarity (I hope).

If a "normal" height mount gives an absolute co-witness then you raise the optic just a smidgen to obtain a "1/3" co-witness.

[ballsout]

An absolute co-witness means that when you look through your iron sights and optic your front sight post appears dead center in your optic with the red dot on the tip.

A lower third (sometimes called a SOCOM) co-witness does the same as above except in the lower third of the optic. You can slightly raise your head position and just view the dot.

So on absolute will the red dot be literally on the tip or resting on the tip?


and if i raise my head won't the dot go further down the front sight?

[Jay Cunningham]

So on absolute will the red dot be literally on the tip or resting on the tip?


and if i raise my head won't the dot go further down the front sight?

An absolute means the sights align with the dot in the dead center of the optic. A lower third co-witness means the sights align with the dot in the lower third of the optic. The red dot will always sit on the tip of your front sight if you are looking through your rear. Remember that optics like the Aimpoint are parallax free, so as long as you can see the dot anywhere in the optic you are going to make your hits.

[ballsout]

Is this correct?

IF it is then is does the optic sit higher since the dot would be in the lower 1/3 of the optic?

[Jay Cunningham]

[ballsout]

think i got it.



in what circumstances would one be better over the other. absolute vs 1/3

and last questions: Does that mean a 1/3 co witness optic will actually sit higher than absolute? Will a added spacer make your optic 1/3 OR is it for going from 1/3 to absolute?

[LOKNLOD]

in what circumstances would one be better over the other. absolute vs 1/3

A lot of it is personal preference. I would say that 1/3 co-witness has all the advantages but none of the drawbacks. Your normal sight picture with the red dot will be less cluttered. On the other hand, I find it *slightly* more cluttered using the irons through the 1/3 co-witnessed optic, but not so much as to undo the value of having the red-dot more visible to me.

and last questions: Does that mean a 1/3 co witness optic will actually sit higher than absolute? Will a added spacer make your optic 1/3 OR is it for going from 1/3 to absolute?

Yes, the 1/3 co-witnessed optic will have to sit slightly higher. Some mounting systems do this by just being designed taller (Larue's mounts for example). Others, like the ARMS mount, use a spacer added into the body of the mount to change the height.

[MX5]

Some people find the sight picture on their RDS "cluttered" and others don't. If you're heads-up with both eyes open, focused on the target or threat and superimpose the red dot, you get hits. Some of us find the sight is nothing more than a obscure blur. I don't even see it anymore unless I focus on the front sight. YMMV. Neither is right or wrong, but a matter of preference.

[Jay Cunningham]

I decided to merge multiple threads discussing this concept and to tack this new combined thread since the question comes up so often.