You really should speak with a CPA, or a tax professional, or your state's small business bureau, as it's a tough call.
Can a business like Best Buy install car radios, offer tech support for computers AND sell DVDs under one corporation, or do they have separate corporations managed by an umbrella corp?
In any case, a business is allowed to invest its money as its governance so chooses. So what you could do, is form three LLCs. One for your photography, one for your real estate, and one responsible for managing the other two. Funnel all your profits into the management company, and distribute investment interest to each of the other two companies.
Or simply form two LLCs, one for photography and one for real estate, invest enough capital into the photography LLC to get it off the ground, and manage the two companies separately.
Or you could have one LLC for real estate, which then invests its profits, and register your photography company as a sole proprietorship.
Hobbist's knowledge of law and wikipedia.