The first 35mm SLR camera was invented in 1935 by a company named Ihagee, who wanted to improve the quality of pictures of its SLR camera by expanding the length of its focus lens. These cameras also gave them faster operation speeds so they could now react quicker and take a picture of something they deemed photo-worthy. They were larger, but more accurate cameras which enabled them to get the picture and angle the photographer really wanted.
When speaking of how this camera effected photojournalism it is really quite simple. The larger focus lens enabled photojournalists to better be able to tell what type of photograph they were taking and what it contains, and the easier operation made them be able to snap a quick photo if the picture only had a short bit of time before it would go away. These luxuries helped photojournalists better be able to encapture the exact photo they wanted, which in turn assisted them in telling the story they really wanted to.
I took the photo I did below with my Iphone 4. I went to Fenway Park last night and wanted to get a good picture from the view of my seat, while also capturing some of the history of the team by getting the retired numbers in the picture. Many advantages of this camera; its viewing lens, its quick action, etc. were originally stemmed from the 35mm SLR. Now with this technology there are just more advances that were added on to the camera such as zoom capabilities, add-on lenses, photo editing, flash, and things like that. So if it were not for the 35mm SLR this technology would not exist, but as with all things it continues to evolve.
Essay Sources: http://slrcameras.ajaxnetphoto.com