  Highly multiplexed spectroscopic surveys have changed the astronomy landscape
in recent years. However, these surveys are limited to low and medium spectral
resolution. High spectral resolution spectroscopy is often photon starved and
will benefit from a large telescope aperture. Multiplexed high-resolution
surveys require a wide field of view and a large aperture for a suitable large
number of bright targets. This requirement introduces several practical
difficulties, especially for large telescopes, such as the future ELTs. Some of
the challenges are the need for a wide field atmospheric dispersion corrector
and to deal with the curved non-telecentric focal plane. Here, we present a
concept of Multi-Object Spectroscopy (MOS) mode for TMT High-Resolution Optical
Spectrograph (HROS), we have designed an atmospheric dispersion corrector for
individual objects that fit inside a fiber positioner. We present the ZEMAX
design and the performance of the atmospheric dispersion corrector for all
elevations accessible by TMT.
