Anytime you sell property, you only owe tax if you have a gain, that is if you sell the property for more than your adjusted cost basis. For most personal property, your adjusted cost basis is whatever you paid for it originally. (For gifted property, your cost basis is what the original give her paid, and for inherited property, the cost basis is the fair market value on the date the previous owner died.)
Business property is a little different, because taking a deduction for depreciation an expense reduces the cost basis. For example, suppose you had a lens that cost $1000 new and you immediately put it into use as business property, and you had fully depreciated it over five years of business use. It’s adjusted cost basis would be zero, so the entire $216 selling price would be a type of capital gain called “depreciation recapture” and would be taxable income (because it is a recovery of a previous deduction).
However, if this particular lens was never listed as a business asset and was never depreciated, then it’s adjusted cost basis is whatever you paid for it when you acquired it, new or used, and you only have taxable income to report if you sold it for more than you originally paid for it.
Separately, even if you later sell equipment that was part of your business assets, you would not open a new schedule C just to report income from the sale. It would be a capital gain if you sold it for more than the adjusted cost basis. It would be reported on schedule D as a capital gain, not as business income. You would only start filing a schedule C again if you decided to go back to photography as a “ongoing trade or business.“
