We present BV photometry of the Galactic globular cluster ( catalog NGC~5286 ) , based on 128 V frames and 133 B frames , and covering the entire face of the cluster .
Our photometry reaches almost two magnitudes below the turn-off level , and is accordingly suitable for an age analysis .
Field stars were removed statistically from the cluster ’ s color-magnitude diagram ( CMD ) , and a differential reddening correction applied , thus allowing a precise ridgeline to be calculated .

Using the latter , a metallicity of { [ Fe / H ] } = -1.70 \pm 0.10 in the Zinn & West scale , and { [ Fe / H ] } = -1.47 \pm 0.02 in the Carretta & Gratton scale , was derived on the basis of several parameters measured from the red giant branch , in good agreement with the value provided in the Harris catalog .

Comparing the ( catalog NGC~5286 ) CMD with the latest photometry for ( catalog M3 ) by P. B. Stetson ( 2008 , priv .
comm .
) , and using VandenBerg isochrones for a suitable chemical composition , we find evidence that ( catalog NGC~5286 ) is around 1.7 \pm 0.9 Gyr older than ( catalog M3 ) .
This goes in the right sense to help account for the blue horizontal branch of NGC 5286 , for which we provide a measurement of several morphological indicators .
If NGC 5286 is a bona fide member of the Canis Major dwarf spheroidal galaxy , as previously suggested , our results imply that the latter ’ s oldest components may be at least as old as the oldest Milky Way globular clusters .