"Enlarging" with a fresnel sheet magnifier?

[mabman]

Interesting. As it happens I also have an (ugly, but functional) Graphic w/ focal plane shutter that I planned to make a pinhole for, but haven't gotten around to it yet...

[michaelbsc]

I think Jorj point that the sheet lenses you find in book stores have a short focal length isn't to be ignored.

Wonder where you could find them with longer focal lengths? Of course that would kind of defeat the light gathering function, so that's probably not a desired characteristic for most lens makers.

And with an aperture the size of a graphic lensboard the light falloff would probably be horrific.

Still might beat a Holga.

[Ottrdaemmerung]

Would such a fresnel sheet be useful for placing in front of the ground glass of a view camera to enhance it?

[holmburgers]

Interesting. As it happens I also have an (ugly, but functional) Graphic w/ focal plane shutter that I planned to make a pinhole for, but haven't gotten around to it yet...

*thumbs up*

Terry, by many accounts these magnifiers work quite well for enhancing a ground-glass. I'll be trying soon, but haven't gotten around to it. There's a thread here that discusses it.

[TimmyMac]

Sorry but you are wrong. http://science.howstuffworks.com/question244.htm

Fresnel lenses can be used in enlargers but only between the light source and the negative. As I said they are not good for imaging.

Huh?

Aren't fresnel lenses used in multi-kilobuck Canon green ring lenses?

[Gerald C Koch]

The Canon lenses use a multilayer diffractive optical element. The pattern seen through a DO lens may look similar to that of a Fresnel lens but other patterns other than concentric rings are also used. Diffractive elements are thin phase elements that operate by means of interference and diffraction to produce arbitrary distributions of light or to aid in the design of optical systems. A pattern is etched onto the surface of the DO element and is only a wavelength or two deep. In a Fresnel lens, the rings are much, much deeper and they work by refraction rather than diffraction. So the Canon DO lenses do not use a Fresnel element.

[Gerald C Koch]

The Fresnel lens was invented by a frenchman by the name of Augustine Jean Fresnel in 1822. Its purpose was to concentrate the light from lighthouses and make them more effective in warning ships.

An interesting fact, in pronouncing his name and the name of the lens he invented the 's' is silent so it is pronounced "frenel". The french appear to have an aversion to the sound of 's' in some words. This can be seen in many cognates. For example, ecole, foret, arret; the English words being school, forest, and arrest or stop.