There are further Stargate props that are no more than two-dimensional or semi-three-dimensional (jar-lid shaped) Stargates, being more lightweight and easier to erect on location. These are always filmed front-on to preserve the illusion. If a shot involves the iris, this is added in post-production, as the mechanics of it opening and closing would be very difficult to build. However, when a Stargate is filmed with just a closed iris (i.e. without it moving), a tangible prop is inserted into place.