Add the 4 cups of fruit, 1/2 cup of sugar, and 1 tablespoon of lemon juice (if using) to a blender body and blend until completely smooth. If the blender is struggling, add some water until it blends easily.
Line a dehydrator tray with a dehydrator sheet or silicone mat and pour the puree evenly onto it. Use a spatula to spread puree evenly over the tray. Be sure there aren't any holes or clumps in the spread. Even drying is the key to quality fruit leather that will last without molding.
Stack filled trays in the dehydrator and turn it on. Set the dehydrator to 135 F/57 C.
Start checking the fruit leather for doneness** at the 4 hour mark. It may take up to 6 hours; possibly 8 hours, if you're environment is humid.
Remove the fruit leather from the liner and allow it to cool. It should come off the liner easily; if it sticks or is still mushy, you know it needs more dehydrating time.
Cut the fruit leather into bite size pieces, strips or dothe classic fruit roll-up thing. Store in plastic or glass one month at room temperature and about a year if tightly wrapped and placed in the freezer.
You can also put wax paper or butcher paper in between yourrolls of homemade leather to ensure they don't stick to each other.