by Lorgar » 28 Aug 2017, 2:14 pm
"Dot sight" is really a label of convenience rather than a type of sight as defined by its functionality, any dot scope you're looking at likely would be a reflex scope.
On a reflex sight, a reticle is projected from the rear of the sight onto the objective lense which reflects it back at the user, hence "reflex'.
More often than not this reticle will be a dot, hence the nickname. But there are reflex sights with crosshairs, concentric circles etc. whatever you want. The "dot" is actually irrelevant to the type of scope or way it works.
Like bladeracer said you can get non-powered reflex sights. My understanding is they use some luminescent material to produce a light source without batteries. But the functionality as it concerns the reticle is the same.
The nature of how a reflex sights work means manufacturers have to manage a balancing act with the objective lense. On one hand it has to function as a mirror and reflect the reticle back to the user, on the other it has to allow light to pass through from the other side to the shooter so they can see through it.
Tipping the balance too much either way, means either a less prominent reticle or an increasingly darker view through the lense. Quality lenses manage this with clever coatings, but on cheap sights you will see the problem.
So, in most cases a "dot sight" is a reflex sight.
Where these style of sights do differ is reflex sights vs holographic sights.
A lot of the following sounds like splitting hairs, I know, especially as the tangible result (a visible reticle) is similar. At the end of the day both types of sight put a reticle on a bit of glass for you to look at, the difference is how it's produced.
I'll have a crack at explaining this but honestly, the technical intricacies of holograms are a bit beyond me. Google holography to learn in more detail how it works if you're really interested, but here's the layperson version I can manage.
The lense of a holographic scope is made of several layers of glass. Using beam splitters and filters etc. an image (photo) is taken of a reticle, then that image is reconstructed in the glass of the sight, as opposed to simply being bounced off it.
Because the reticle doesn't have to be reflected, the objective lens doesn't require that mirror element like a traditional reflex sight does; you have a clear view through the sight to targets beyond, unobstructed by filters or lens coatings.
A catch with holographic sights though is that the reconstructed reticle is polarised. If you're trying to use one while wearing polarised glasses, the reticle will be diminished or filtered out. And all this technical wizardry uses a fair amount of juice, so holographic sights are always powered and battery life is significantly less compared to the relatively simple reflex scopes.