Why Do Anamorphic Lenses Produce Horizontal Flare

[Peter Ellner]

I'm curious as to why anamorphic lenses make such a unique horizontal lens flare that's so recognizable? What actually causes this effect to occur?

 

Thanks so much!

[Chris Millar]

Best method for investigating lens bokeh, flare and coverage falloff is to put your eye in the focal plane of the lens in question and look at the colours you see projected from it - sometimes it becomes very obvious what is going on, big bright hotspots of accumulated refraction, lens hoods and casings catching unwanted light, scratches hitting a sweetspot of intensity, spectra becoming more and more intense in one particular colour etc...

 

Point sources of 'real' white light in a black room can be good testers to point them at

 

Never had a chance to do it with a scope lens though - someone might be able to fill us in

Edited May 29, 2011 by Chris Millar

[David Mullen ASC]

Anamorphic lenses use an element that, from the front, looks like a glass barrel standing up. This is the element that squeezes the image on the horizontal axis. Most anamorphic prime lenses have this cylindrical element in front for greater sharpness and speed (compared to adapted anamorphic lenses like zooms and telephotos that put a small anamorphic element at the rear of the lens.)

 

So since the front of the lens is a barrel-shaped cylinder of glass, a bright point of light basically smears across the surface on a horizontal axis. The lens coating usually gives this flare a blue-ish cast.

 

You can see some pictures of anamorphic lenses here:

http://owyheesound.com/images/krasnogorsk-3_w_lomo_anamorphic_lens_2.jpg

http://owyheesound.com/anamorphic.php

 

Since from looking at the lens directly from the front, the cylindrical element looks square-ish, this is one reason why rear-adapted telephoto anamorphic lenses sometimes produce a square-shaped bokeh.