Question

with new digital cameras, the user simply presses on a button to take a picture. the camera focuses the image using a sensor to detect the subject. but up until the 1980s, professionals and amateurs alike used manual film cameras to take photographs. on a manual single lens reflex (slr) camera, there is a ring on the lens, which is turned to sharpen or blur the subject. a viewfinder sits on the top of the camera and the photographer must look through it to ensure the subject is in focus. slr cameras require

solvents

fission

manipulation

tutorials

Explanation:

The sentence is about SLR cameras requiring an action related to focusing (sharpen or blur the subject). "Manipulation" fits as adjusting the lens ring to focus involves manipulating the lens. "Solvents" (chemicals), "fission" (splitting, like in physics), and "tutorials" (instructions) don't relate to the camera's focusing action.

Answer:

manipulation