Why are Tube Red Dots so Big?

[NorCalRefuge]

Micro Red Dots are all the rage now, for being small and light, etc.

Full sized red dot sights are much larger - not only in aperture size, but also the length!

Aimpoint CompM4 with 23mm aperture and length of 4.7 inches:

https://www.aimpoint.com/product/aimpoint-compm4/

Aimpoint T2 with 19mm aperture and length of 2.7 inches:

https://www.aimpoint.com/product/aimpoint-micro-t-2/

The same trend holds true for most/all manufacturers, such as Vortex, and more.

Does anyone know why a larger aperture usually means getting a long toilet paper tube of a RDS? Surely someone can make something the size of a T2 but with glass as large as the M4? Trijicon kind of does this with the MRO, why are there not more micro sized RDS with large glass?

[Scotty]

Think of it like a triangle. The LED diode is at the adjacent and hypotenuse leg. The lens is on the opposite leg. If you grow the length, the distance to the diode grows in order to maintain the same angle. If you were to try to shorten the length, you would need to either angle the front lens more or modified the diode side curvature which leads to more distortion.

[osis32]

I like the bigger window and they can take more punishment.

[The War Wagon]

I like the bigger window and they can take more punishment.

Not sure about the latter, but I can relate to the former. I ran Comp M2's for a long time, and until the mini's came out with 2moa dots, they suited me fine.

[theduracellbigd]

Its America, bigger is better. HaHa
I like larger windows. I think length might have to do with dot imaging and parallax free , idk.

[NorCalRefuge]

The ruggedness argument used to be true, but today's micro RDS can take a beating from everything I've seen & read. Even the cheaper ones...

[NorCalRefuge]

Think of it like a triangle. The LED diode is at the adjacent and hypotenuse leg. The lens is on the opposite leg. If you grow the length, the distance to the diode grows in order to maintain the same angle. If you were to try to shorten the length, you would need to either angle the front lens more or modified the diode side curvature which leads to more distortion.

Ah, Scotty - you are right!

Thought about what you said for a bit, and came up with this awful diagram to illustrate the point you were making.



The grey is the larger sized optic. Since the diode needs to be somewhere out of sight, it does require a longer tube to keep the same dot position relative to the eye - otherwise the glass would have to be concave/convex quite a bit to achieve the same, and then you wouldn't have a true 1x anymore.

[teflondog]

The Trijicon MRO is a good example of the disadvantages of a red dot sight that is both short and wide. The curvature of a large objective lens becomes more noticeable as you reduce its distance from the ocular lenses. Many people described this as magnification although it's technically distortion. When people look through my MRO, a lot of them say that it feels like they're looking through a prescription lens. Trijicon reduced the amount of distortion during a revision change (post 89k serial number) by altering the objective lens, but there is still a bit of distortion in the current models.

[NorCalRefuge]

The Trijicon MRO is a good example of the disadvantages of a red dot sight that is both short and wide. The curvature of a large objective lens becomes more noticeable as you reduce its distance from the ocular lenses. Many people described this as magnification although it's technically distortion. When people look through my MRO, a lot of them say that it feels like they're looking through a prescription lens. Trijicon reduced the amount of distortion during a revision change (post 89k serial number) by altering the objective lens, but there is still a bit of distortion in the current models.

MRO's also have a strong blue tint to them, from what I've seen.

[teflondog]

MRO's also have a strong blue tint to them, from what I've seen.

The ones with a pre 89xxx serial number had a significant blue tint. I just purchased one with a 173xxx serial number and the blue tint is dramatically less. I would say it's just slightly more blue than my Aimpoint T1 and way less blue than my RMR v1.

[NorCalRefuge]

The ones with a pre 89xxx serial number had a significant blue tint. I just purchased one with a 173xxx serial number and the blue tint is dramatically less. I would say it's just slightly more blue than my Aimpoint T1 and way less blue than my RMR v1.

Good to know!

[Scotty]

MRO's also have a strong blue tint to them, from what I've seen.

Most red dot lenses will have a tint to them. It's to help you see the dot and it is also part of the beam splitter. The front lens is working as both a beam splitter and a collimating lens.

If you don't know what a beam splitter is, it's basically like a 1 way mirror. It allows you to see the reflection and also through the lens. The coating needs to be on the near side so you don't get a secondary reflection off the farside surface. If you place your cellphone on the dash with the display pointing up, you'll see 2 reflections on the windshield. The beam splitter coating stops that.

The curvature of the lens acts as the collimating lens, basically that focuses the red dot out to infinity.

I'm not a optics engineer, but I had to learn all this stuff when one of my projects at work was to reverse engineer and build a helicopter helmet mounted sight for a foreign military. It was basically a light source, reticle, collimating lens, and a beam splitter.

[NorCalRefuge]

Most red dot lenses will have a tint to them. It's to help you see the dot and it is also part of the beam splitter. The front lens is working as both a beam splitter and a collimating lens.

If you don't know what a beam splitter is, it's basically like a 1 way mirror. It allows you to see the reflection and also through the lens. The coating needs to be on the near side so you don't get a secondary reflection off the farside surface. If you place your cellphone on the dash with the display pointing up, you'll see 2 reflections on the windshield. The beam splitter coating stops that.

The curvature of the lens acts as the collimating lens, basically that focuses the red dot out to infinity.

I'm not a optics engineer, but I had to learn all this stuff when one of my projects at work was to reverse engineer and build a helicopter helmet mounted sight for a foreign military. It was basically a light source, reticle, collimating lens, and a beam splitter.

Nice insight there! Sounds like some interesting work you've done