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How Does a Slide Projector Work?

By Dillon Wallace

Slide projectors or viewers were all the rage decades ago, particularly for education purposes. Then, technology got the best of it with the ushering in of the digital age. 


But, have you ever wondered how those little tiny transparent slides delivered full-blown images when placed in the projector?


Well, you’re about to.


Let there be light

Slide projectors, viewers, carousels … whatever you want to call them function on a pretty simple premise. When light from the projector is shined through specialized photographs (AKA slides), it enlarges the photograph on the slide and displays the image on a screen or wall.


Simple, right? 


Well, it’s just a little more complex than that.


Inside the projector are several lenses and mirrors that it uses to project parallel rays of light through the slide. While this is happening, a lens on the other side of the slide spreads the light rays back out, enlarging the image. That’s where the focus feature of the lens comes in handy, in order to make each projected image sharp and clear. The size of the image can be adjusted by moving the projector further from or closer to the wall or screen it’s projecting on. Of course, limitations of the lenses come into play when you try to enlarge the image too much, compromising clarity.


Click, click, click

Similar to a cylinder on a revolver, projectors use a magazine to hold many different slides. Dozens of them. When the user clicks the button, the slides advance in a consecutive carousel fashion and a new slide is projected.


So, there you have it – the 411 on how slide projectors work.


Do you have old slides ready to digitize?

If you’ve got a box full of old 35 mm slides (there were several formats of them), you’re sitting on a goldmine of memories. Lucky for you, we can help. Send them in to us and we’ll digitize them for you via DVD, thumb drive or cloud download. No projector necessary. Just friends, family and a box of tissues to enjoy them.

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