  Recent developments in magnetic field sensing with negatively charged
nitrogen-vacancy centers (NV) in diamond employ magnetic-field (MF) dependent
features in the photoluminescence (PL) and eliminate the need for microwaves
(MW). Here, we study two approaches towards improving the magnetometric
sensitivity using the ground-state level anti-crossing (GSLAC) feature of the
NV center at a background MF of 102.4\,mT. Following the first approach, we
investigate the feature parameters for precise alignment in a dilute diamond
sample; the second approach extends the sensing protocol into absorption via
detection of the GSLAC in the diamond transmission of a 1042\,nm laser beam.
This leads to an increase of GSLAC contrast and results in a magnetometer with
a sensitivity of 0.45\,nT/$\sqrt{\text{Hz}}$ and a photon shot-noise limited
sensitivity of 12.2 pT/$\sqrt{\rm{Hz}}$.
