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View Full Version : Red-dot vs. Holographic sights


radioflyer
March 20, 2011, 09:57 PM
I'm having trouble understanding the difference. The First AR I shot had an Eotech sight and I'm not understanding how this differs from a Red-dot sight.

Can anyone explain?

thank you

Ridge_Runner_5
March 20, 2011, 10:53 PM
Red dot sights project an LED onto the glass
Holos like the EOTech fire a laser

radioflyer
March 20, 2011, 11:02 PM
Isn't a laser in the eye a bad for the retinas? How does the holographic design get around this?

wogpotter
March 21, 2011, 09:43 AM
While a laser is used in a holographic sight it isn't "fired" at anything other than an internal reticule (the hologram) so it is 100% eye safe.:rolleyes:

The difference lies in where the projected reticule or dot appears to be to the eye.

A red dot shines a focused image of a small LED, or pattern made of LEDs at a coated glass "lens" or plate. You look through the glass & the eye superimposes the red dot (or pattern) on the target behind the glass. The optical system uses a few tricks to let your eye focus on the dot & the target at the same time.

A holographic sight uses a hologram (laser created pattern) which is lit by a matching laser to the type used to make the reticule. Basically a Hologram is an interference pattern caused by interaction between splitting & recombining a laser beam, the usual example given is dropping a rock into still water & looking at the multiple overlapping wave patterns. The holographic pattern has some odd qualities, such as being able to recreate 3D objects & even look behind them if done correctly. This is used to "create" a "Virtual" dot, or pattern that is not inside the sight, but fairly long distance in front of the physical sight unit.

To use a holosight you look at the target way out there with both eyes & just allow the brain to recombine all the information into a single image. The effect is of a reticule floating in space 15~30 feet in front of the gun.

The effect gives some advantages such as not mattering if your eye is off center when sighting.

radioflyer
March 22, 2011, 12:15 AM
so with a red dot sight, the dot appears to be just over the targeted area where a holographic sight, the dot appears to be actually ON the target depth wise.

Double Naught Spy
March 22, 2011, 05:46 AM
so with a red dot sight, the dot appears to be just over the targeted area where a holographic sight, the dot appears to be actually ON the target depth wise.

Personally, I don't see that when I look through them.

One difference is that Eotech holographic sights all for more light transmission. The coating on the inside of the front glass on which a red dot is projected and reflected darkens the sight ever so slightly. For me, it has only been an issue at distance during low light.

grumpa72
March 22, 2011, 07:10 AM
My Eotech dot appears to hover in front of the lens and it is very easy to adjust to how it appears. Here is an example, my wife had never shot a rifle of any sort and had two sessions at the range using hand guns. I gave her my Eotech equiped AR and she shot a six inch circle at 50 yards. Not bad. While I have no experience with red dots, I am sold on the holographic sights. There is no paralax (sp?) and where ever you see the dot is where the bullet is going, even if you hold the rifle off center.

Double Naught Spy
March 22, 2011, 07:23 AM
Red dots really aren't different in that reguard. Some people perceive the dot down range somewhere as I have watched them put their hand in front of the optic. Parallax isn't an issue with decent reds dots and there are plenty in the price range of an Eotech, which is a very good optic.

Some are considerably less expensive and still good...
http://thefiringline.com/forums/showthread.php?t=444467&highlight=vortex

wogpotter
March 22, 2011, 08:20 AM
Where the shooter perceives the sight to be depends on where & how they look.

To really get the effect of the holographic reticules you have to train yourself to look at the target directly with both eyes open, ignoring the sight "frame" completely. In effect you stare past the sight to the target. Once you get the technique down the holographic reticule "floats in space out there between the sight & the target." Very hard to describe, but very easy to use in practice.

Here's a (poor) picture of a holographic sight reticule. The target, & reticule are pin sharp in reality & you can't really get the 3-D effect with a camera.
http://i60.photobucket.com/albums/h29/moosp/DSCF6406.jpg

Both types of sight have a coating on the lens, but some are stronger (darker) than others. You can see the greenish tint in the lens in the picture.