The Art of Projection: How Convex Lens Enhance Projectors

Convex lens are indispensable for projectors. Convex lens enhance projectors by helping them project magnified & focused images. But have you ever wondered if it’s a bit counter-intuitive? Despite learning that convex lenses typically produce diminished, inverted images, they managed to create magnified images in projectors.
If this puzzles you, then you are at the right place. In this article we will try to demystify how projectors achieve magnified, focused images.

The assumption that a single convex lens in a projector is producing magnified and yet focused image is wrong. A projector contains an array of lenses and a lot of other components that help it to produce a focused & magnified image.

So, what are the components of a projector?

Projector is a complex machine with several key components. It includes light source, condensing lens, LCD panels, color wheels, projection lens, aperture and many more. However, to keep the discussion limited to the overall optics of image formation, we will be discussing certain specific components in this article.

Light Source: High intensity lamps or LEDs that illuminates the whole picture
Concave mirror: the concave mirror gathers and reflects scattered light from the light source , directing it toward the condenser lens. Without this mirror, much of the light would spread out and be lost. The mirror captures and focuses this light for better projection.
Condenser lens (for Light Concentration): Two plano-convex lenses are positioned near the light source, to gather light which would otherwise spread out and be wasted & focus the light into a beam, directing it toward the image-forming element (LCDs)
LCDs: Many projectors use Liquid Crystal Display (LCD) panels that control light passage through tiny pixels to create the image. It is the image formed in the LCDs that get projected on the big screens
Projection lens: this is a convex lens that magnifies & focuses the image created by the LCDs and projects it to the big screens. The projection lens is moved to & fro in the lens barrel until a sharp magnified image is produced on the screen.

Image magnification & focusing by projection lens (convex lens)

The image becomes sharper and more focused where the light rays converge after passing through the convex lens.
Inside the projector, the image on the slide acts as a light source. Light rays from each point (or pixel) of the image are refracted by the projection lens and then converge on the screen, creating a clear, magnified, and focused image. While it may seem like the light rays are diverging, they are actually converging from all individual pixels to form the final image on the screen. Below, you’ll find detailed schematics illustrating how the projector achieves this.

The LCD is positioned very close to the lens barrel. Within the lens barrel, the projection lens can be adjusted back and forth to project a focused image onto the screen. Typically, the LCD (image) is placed between the radius of curvature and the focal point of the projection lens, resulting in a magnified & focused image. Below we’ve given you a representation of how each individual pixel from the image is getting magnified & focused,

The projectors are designed in such a way that provide focused projection beyond the focal point.

The image remains in focus because the projector lens system is carefully calibrated to ensure formation of a clear image at the screen’s location. The following aid the projector in producing a focused projection:

Lens Assembly: Often, projectors use multiple lenses to correct any distortions that might occur as light rays of different wavelength converge. These lenses work together to focus the light rays into a sharp, coherent image on the screen.
Focus adjustment controls: By adjusting this distance, you can ensure that the image projected onto the screen remains sharp. This is why projectors have focus adjustment controls—to fine-tune this distance and achieve a clear image.
Lens Quality and Design: The design of the lens also plays a crucial role. High-quality lenses minimize optical aberrations and ensure that the rays of different wavelengths converge at the same point.