Hello! I imaged M67 on 18-April and 1-May with my 8 inch LX200 classic at f6.3 using BVI filters and an SBIG ST-402 camera.
After using the photometry wizard in MPO Canopus with the same 15 stars from Mr. Henden's field, I obtained the following transforms: 18-April B=0.529, V=-0.065, I=-0.006
01-May B=0.135 V=-0.051 I=-0.017
The error plots for each night were very close to zero with small standard deviations.
The transforms for V and I seem close. B seems quite different on the two nights. How much variation should I expect? Thank you and best regards.