What Makes a Lens a Petzval?

Fotoguy20d

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I've seen old brass lens listed as being petzval lenses. What makes a lens a petzval and what makes it special?

Thanks,
Dan
 

Q.G.

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A Petzval lens is a very old, very simple lens design, consisting of two positive doublets, one on each side of the aperture.
Decent image quality, but over a limited field. And for its period (mid 19th century), very fast.

What realy made it special - its claim to fame - is that it was one of (or perhaps the) first lenses that were calculated, and not just made up relying on experience and craftmanship.

Being rather simple - thus cheap -, fast, and pretty good, it was popular for a while.
 

jimgalli

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The Petzval was designed in 1840 and is generally considered to be the first mathematically designed lens. There's a good page about them Dead Link Removed The design has a signature effect of extreme center sharpness that is very shallow and falls off to excellent oof bokeh. Pushed beyond their design constraints they get the additional effect of swirlyness out in the far edges which people seem to like. The signature effect really lends itself to portraiture where the sharp center is all you really need to draw attention to your subject.
 

brian d

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Just look at mr. Galli's work and you will see what makes it special
 

smieglitz

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Probably should mention that just because a brass lens is old, that doesn't make it a Petzval. There were other designs such as Rapid Rectilinears, etc., that were contemporary with Petzvals and look similar externally.

Petzvals exhibit a certain roundness and three-dimensionality in the way they render images and this, along with their great speed made them desirable for portraiture.
 
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