fresnel lenses

[jimdesu]

Quickie Q for anyone who knows:

 

Does the scheimpflug affect apply to Fresnel lenses?

 

thanks

 

James

[jim kerr]

James, Guess I'm just dumb, never ran across the term "scheimpflug Effect " before, care run over that in English or American would you?....Jim

[jimdesu]

Assuming I haven't misspelled it, it's the ability to alter the plane of focus by tilting the lens, so that points of varying distance from the camera can be in focus simultaneously.

[Ed_Ingold]

Insofar as a Fresnel lens is a simple lens "collapsed" to retain the curvature but not the bulk, it would exhibit the Scheimflug effect. It might be hard to tell, since the resolution is not very good.

[alex_lofquist]

Yes.

[grahams]

"It might be hard to tell, since the resolution is not very good."

 

It depends on the lens in question. Historically, fresnel lenses were mainly only used in luminaires, lighthouses and such, and as part of the viewing screen of camera viewfinder systems, as I am sure you all know. However, Canon are now using fresnel lens elements in some of their latest zooms - designated "DO" for "Diffractive Optics". With this technology, the resolution is very good indeed.

[winfried_buechsenschuetz1]

"However, Canon are now using fresnel lens elements in some of their latest zooms - designated "DO" for "Diffractive Optics"."

 

Not quite true. Fresnel lenses 'shape' light beams by refraction.

 

Refraction and diffraction are two different things. Refraction always needs two mediums of different refraction index (usually glass and air), and in most cases surfaces of different curvature (glass elements with two plane surfaces also cause refraction but this is rarely used for photographic optics). Diffraktion works without difference in refraction index, diffraction is caused by structures with dimensions close to the wavelength of radiation.

 

The structure of the diffraction elements in the new Canon lenses looks very similar to the structure of a fresnel lens but actually is NOT a fresnel lens.