  The ability to measure precise and accurate stellar effective temperatures
($T_{\rm{eff}}$) and surface gravities ($\log(g)$) is essential in determining
accurate and precise abundances of chemical elements in stars. Measuring
$\log(g)$ from isochrones fitted to colour-magnitude diagrams of open clusters
is significantly more accurate and precise compared to spectroscopic $\log(g)$.
By determining the ranges of ages, metallicity, and extinction of isochrones
that fit the colour-magnitude diagram, we constructed a joint probability
distribution of $T_{\rm{eff}}$ and $\log(g)$. The joint photometric probability
shows the complex correlations between $T_{\rm{eff}}$ and $\log(g)$, which
depend on the evolutionary stage of the star. We show that by using this
photometric prior while fitting spectra, we can acquire more precise
spectroscopic stellar parameters and abundances of chemical elements. This
reveals higher-order abundance trends in open clusters like traces of atomic
diffusion. We used photometry and astrometry provided by the \textit{Gaia} DR3
catalogue, Padova isochrones, and Galactic Archaeology with HERMES (GALAH) DR4
spectra. We analysed the spectra of 1979 stars in nine open clusters, using
MCMC to fit the spectroscopic abundances of 26 elements, $T_{\rm{eff}}$,
$\log(g)$, $v_{\rm{mic}}$, and $v_{\rm{broad}}$. We found that using
photometric priors improves the accuracy of abundances and $\log(g)$, which
enables us to view higher-order trends of abundances caused by atomic diffusion
in M67 and Ruprecht 147.
