Originally Posted by
R.K
So in accordance with post above, the Fresnel on the cameras is a special Fresnel, not just a regular Fresnel lens. Well, some people on this great forum like to make a posts even when they not sure are they right or not.
So, some information for the poster above. On the cameras the Fresnel lens used for the same purpose as on the light houses and any other lighting devises – to combine the rays of light falling on it, make those rays parallel to each other and perpendicular to the flat face of the Fresnel lens. As known the ground glass not only a focusing device, it is in the same time a good reflector and diffuser. So when the Fresnel placed under the ground glass it can combine all light falling on it and send a powerful parallel ray of light though the ground glass to make the focusing work much easier. Of course as any other surfaces the Fresnel also reflecting some light back, but because it is clear and made from the special optical material it reflect much less light then the ground glass. So when the Fresnel located under the ground glass it really help. Some people like to locate Fresnel on the top of the ground glass. This is possible to. But what the Fresnel really doing in that arrangement, almost nothing. In that arrangement the ground glass already reflect some sufficient amount of light back in the camera and this light will never any more reach the Fresnel and the photographer.
Bookmarks