We report a singly resonant optical parametric oscillator (SRO) based on a ${\mathrm{ZnGeP}}_2$ crystal directly pumped by a lamp-pumped Q-switched $\mathrm{CrTmHo}:\mathrm{YAG}$ laser. The IR was tunable from 4.7 to $7.8\mathrm{\mu }\mathrm{m}$ via crystal angle tuning. A maximum optical to optical efficiency of 56% was obtained from the pump $\left(2.09\mathrm{\mu }\mathrm{m}\right)$ to total IR at a pump energy of $6.5\mathrm{mJ}$ . The corresponding idler energy was $1.45\mathrm{mJ}$ . The SRO was measured to have a slope efficiency of 64% and a threshold of $1\mathrm{mJ}$ . The spatial beam quality of the idler, characterized by the $M^2$ parameter, was 1.38 when the SRO was pumped at 2.5 times threshold. These results show that ${\mathrm{ZnGeP}}_2$ optical parametric oscillators directly pumped by a $\mathrm{CrTmHo}:\mathrm{YAG}$ laser can be operated efficiently, while maintaining good IR beam quality.