TS-Optics Erecting Lens 1,5x - 1,25 inch for refractor telescopes
Each refractor shows an upside-down image with sides mirrored if it is used in direct vision (without star diagonal).
With this accessory, the image is upright again and, if an Amici prism is used, not mirrored anymore. On the other hand, the view is angled by 90° or, with Amici prisms for terrestrial use by 45° angle instead.
Especially when viewing at daylight, one often wants to look into the same direction as the telescope. The erecting lens solves this problem and you have a correct image orientation in your telescope, but without angled insight.
The erecting lens also works great with nearly any type of telescope, apart from Newtonian telescopes. At Schmidt-Cassegrains, Maksutov telescopes and refractors, it even replaces the star diagonal. That is useful if you want to view straight through the telescope. Here, it also offers a correctly orientated image where up is up and left is left.
1 Erecting lens
Provides correct up/down and left/right orientation with direct vision when using refractors