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View Full Version : What Is Effect of Hole Shape in Waterhouse Stops?



Richard K.
02-14-2010, 07:14 PM
I've seen many Waterhouse stops with ROUND holes but recently I've seen one with a square aperture. How will this affect the image compared to the more usual round aperture? Is Bokeh affected? Thank you!

Oren Grad
02-14-2010, 07:59 PM
Is Bokeh affected?

Yes.

http://www.luminous-landscape.com/essays/bokeh.shtml

Nicholas Lindan
02-14-2010, 09:29 PM
Square waterhouse stops are used in process lenses. The geometry of the stop is aligned with the direction of the dot-screen when half-tones are made for reproducing photographs.

calceman
02-15-2010, 01:57 PM
Maybe this could help...

http://www.apug.org/forums/forum44/65726-shape-opening-waterhouse-stops.html

Jeff Searust
02-15-2010, 02:10 PM
I have seen them as star shapes also -- The theory is that you are letting a volume of photons through a hole. The shape of the hole is irrelevant, the area of the hole is relevant. And it WILL affect the image.

polyglot
02-15-2010, 06:55 PM
What you get in the image (ignoring lens issues like spherical aberration, etc) is the convolution of your aperture (stop) with every point in the scene, with the size of the aperture-image scaled by how far from the plane of focus the point is. So stuff in focus varies only in brightness with the area of the aperture, stuff that's out of focus will vary in shape.

The usual cliche is to make heart- and star-shaped cardboard stops for a 50/1.4 (35mm-equivalent), put a loved-one in front of christmas-tree-lights and fire away. You get glowing coloured hearts etc in the background.