Check Loris's links. Karakoy and Eminonu are the two sides of the Halic River connected with Galata Bridge. If you go to Taksim Square , Beyoglu or Bosphorus Sea Side Road , Modern Art Museum , Besiktas , Sariyer , Emirgan , Ciragan Palace and Dolmabahce Palace , Robert College , Bosphorus University ,Bebek they are all at the side of the Karakoy.
If you cross the Galata Bridge and reach to the Eminonu , there is Sultanahmet Mosque , Suleymaniye Mosque , Hagia Sophia , Hagia Cora , Archaeology Museum , Topkapi Palace , Koc Industrial Museum , Sirkeci , Grand Train Station and lots of used camera equipment sellers at Sirkeci and around Grand Post Office at Sirkeci . There is seaside route to Yesilyurt , Yesilkoy there.
There is a serious repair work is going on at Bosphorus Bridges and always prefer a ship route to Anatolian Side Kadikoy or Bosphorus Sea Side Tour via vapur ship from Eminonu or Karakoy or Kadikoy or Besiktas.
Istanbul is 100 times larger than tourists sees and tourists sees the not the nicest places.
Eminonu and Sirkeci Post Office area are the mecca of film photography but analog cameras are very expensive. Buy from ebay. You can buy every film possible from Pamuk Ticaret cheap , 6.5 dollars for 120 Kodak Portra 400 Fresh.
Istanbul is extremelly hot nowadays , buy hat , sunscreen and sunglasses. Try to visit after Ramadan.
Buy lots of train coins ,ship coins ,bus cards , metrobus cards , telephone card for not to need wait later
Its a suicide to visit that city without tour guide books and large maps and updated traffic flow information.
At Sirkeci , you can jump to train and go to Bakirkoy or Yesilkoy beatiful place , walk bus to the sea and turn back to the Sirkeci by bus from sea side route.
You can go to the Kadikoy with Ship , walk to the Moda , find a ship to Prince Islands expecially Buyukada and enjoy.
You can jump to minibus and go to the Bagdat Caddesi and great fun