September 2015 Portraits

[jesse]

Lotus 5x7, Jamin & Darlot cone type Petzval, Fomapan 100, HC-110

[RSalles]

Nice Jesse, both of them,

Cheers,

Renato

[AtlantaTerry]

Lotus 5x7, Jamin & Darlot cone type Petzval, Fomapan 100, HC-110

Would someone please explain to me why the out of focus background swirls yet the subject does not?

Thank you.

[Peter De Smidt]

Would someone please explain to me why the out of focus background swirls yet the subject does not?

Thank you.

That's the nature of a Petzval lens: the center is normal, while the edges are swirly.

[polyglot]

That's the nature of a Petzval lens: the center is normal, while the edges are swirly.

It's not just a centre-vs-edge thing, it's a focused-vs-unfocused variation as well.

Near the edges (well, not the extremes), you can still get a fairly-well focused image, i.e. all the light coming from a single point in the scene ends up largely at one point on the film. But where a point is defocused, the light from each scene-point gets spread out (to a first approximation) into an image of the aperture as seen through the rear element. Because of how the petzval rear group works, the defocusing spread is mostly tangential (in circles around the lens axis), with the effect becoming stronger away from the centre (at wider angles, the rear element looks flatter and more-elliptical to the film), while focused regions are mostly un-distorted.

[Mark Sawyer]

It's not just a centre-vs-edge thing, it's a focused-vs-unfocused variation as well..

Also a specular highlight thing, and only faster (f/4, or there abouts) Petzvals will swirl. There's a bit of learning to get a Petzval to jump through the hoops...