Sennheiser MKH800 Dual Capsule microphone, is not a stereo microphone, it is a unique concept it allows users to make their own polar patterns, explained in an excellent review in the Sound on Sound magazine.
SOUND ON SOUND Say :
The Sennheiser MKH 800. It has two separate cardioid capsules, mounted coincidentally and back-to-back, and each capsule has a dedicated output that can be fed to any standard mic preamp. Because of the versatility of the Twin, it doesn’t feature the four pattern-selection and frequency-response adjustment knobs that were found on the original MKH 800. Its signals can be recorded for later processing and even re-mixing, enabling engineers to make minute adjustments to the sound of the mics.
To read the complete review click here