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The cards in front and at the back of the stage are for colour and tone calibration when I'm editing the images on my computer; they get cropped out of the final images.
I think the colour cards are a good idea.Where did you get the colour and grey scale cards from?Did you make them yourself?
If you're OK with painted scenics, Jon Hodgson Maps on Patreon has a subscription available (I think $3 a month). Very nice artwork, and one month's subs will get you the whole back catalogue.