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New Graflex 23 Camera Fresnel Lens+ Ground Glass. 

 This new type of Fresnel screen and ground glass were made of Hi-Tech optical acrylic, which is the brightest and powerful. This durable product  significantly increase the brightness of the image to make focusing much more easier and accurate.   The circle gap < 0.1mm.

The condition is unconditionally guaranteed.  

 

The Fresnel lens was invented by French physicist Augustine Fresnel, the Augustin Fresnel first used this lens design to build a glass Fresnel lens - lighthouse lens in 1822.
The Fresnel lens is a thin, flat optical lens which consists of a series of small narrow concentric grooves on the surface of a lightweight plastic sheet in order to reduce the thickness, weight and cost. Each groove is at a slightly different angle than the next and with the same focal length in order to focus the light toward a central focal point. Every groove can be considered as an individual small lens to bend parallel Fresnel light waves and focus the light. The lens actually eliminates some spherical aberration.