The given combination gives a zero dispersion and zero average deviation combination of two prisms. But this happens only when the material of the prisms is same. If material of one of them is different, and prism are rotated in such a way that one of deviation or dispersion gets removed, the other would remain.
We can combine two prisms in such a way
- deviation is zero but dispersion is not
- dispersion is zero but deviation is not
But in both situation, both cannot be zero simultaneously.
