I recently had my focusing screen replaced in my Nikon D70 camera to a split prism focusing screen for more precise manual focusing while taking macro photographs. The split prism screen is like the one that was in many film SLR cameras of old, like my precious Minolta X-700 which I used for over 20 years. I have been using the D70 camera now in manual mode for 2 weeks and have not returned to the autofocus mode once. I love shooting macro now, and no longer have to guess if my image is in focus.
I was extremely lucky to win a Lester Dine 105mm lens and a older model Dinecorp point/ringflash on eBay and am having a ball taking photographs of my Japanese morning glory garden.
It cost about 200 dollars to have the focusing screen modified but that included the installation fee (and in reality was about how much I spent on the D70 camera body on eBay LOL). It was money well spent.
Send me a Dmail if you want to learn about the vendor who did the modification.