Instrument using two concave lenses

[songoku]

Is there maybe instrument using two concave lenses? Tried to google it but found nothing.

Thanks

 

[sysprog]

Rays that pass through convex lenses converge; rays that pass through concave lenses diverge $-$ here's a link regarding two concave lenses: https://www.ck12.org/c/physics/double-concave-lenses/lesson/Images-in-Double-Concave-Lenses-PHYS/

 

[Andy Resnick]

Summary:: Microscope uses two convex lenses and there is telescope using combination of convex and concave lens.

Is there maybe instrument using two concave lenses? Tried to google it but found nothing.

Thanks

AFAIK, since two concave lens elements can be made equivalent to two convex lens elements by suitable spacing and focal lengths, there is no compelling reason to use more than one diverging element. In terms of manufacturing, concave lenses are much more difficult to form and mount- thin in the middle and sharp angles at the edge- so there are excess costs associated with concave lenses.

That said, use of diverging lens elements is important for high-power systems because there is no intermediate focal point- no part of the optical system is exposed to extremely high irradiance- and you can find diverging lens systems in unstable resonators and amplifier systems.

 

[songoku]

Thank you very much sysprog and Andy Resnick