On lower budget projects, we sometimes don’t get the luxury of a prep day—or sometimes even if we do, we might only check that the gear isn't broken. But if you’re concerned with the outcome of the final product, I would encourage you to do more thorough testing of your gear, above and beyond the question of whether it functions or not, specifically when it comes to lenses.
Even on the lowest of budgets, you need to know how your lenses behave so you can shoot accordingly. Take, for example, my old Pentax 50mm.
This lens has a cool vintage look, and it’s the only lens that I’ve ever gotten the question, “what lens did you use?“ after showing someone a photo I took.
^This isn't a great photo, but it's an example of how the Pentax looks. Anyways, if you had this lens, you might be inclined to use it for one of your shoots. And that's where the lens test comes in.
Notice the vignette and halation when wide open. That's the "cool vintage look" right there.
So imagine you've just bought this lens on eBay, you pop it on your camera to shoot a quick test clip at f/1.7 and love what you see. You take it on a shoot, but the subject matter you're shooting requires a larger depth of field. You stop down to f/5.6 and now you've lost most of that cool look, but you might not notice until you're seeing the footage on your computer monitor, at which point, it's too late.
Another example: I recently worked on a short film where they chose to use rehoused Canon FD lenses for their glass. The tighter shots looked good, but the wide shots looked fuzzy and had a crazy amount of spherical distortion. Again, a great reason to test—to avoid unpleasant surprises on set.
Side note regarding my test shots: The bottom test card image is noisy because I bumped the ISO up to keep the exposure consistent—DON'T DO THIS! Ideally, you would have enough light on your test card that you could only change the aperture and shutter angle, because changing the ISO affects the sharpness and gives an ambiguous result. I was trying to take these quickly just for the example, but you shouldn't rush through your tests for an actual project!
