Open red dot sights
— in open collimator sights, the main lens is not inside the body, but above it, in a special frame. Such sights are more compact than closed sights and do not block the field of view as much; their main disadvantage is less protection from pollution and damage. In addition, open models tend to “go blind” under bright light (for example, sunlight): in such conditions, the brand may become poorly visible; however, in most models, this moment is taken into account by manufacturers and compensated in one way or another (for example, by high maximum brightness).
In general, it is worth paying attention to open collimators in cases where the ability to quickly shoot offhand and maximum control of the situation are of key importance.