Petzval focal length vs coverage?

[athanasius80]

Is there a general rule for the coverage of a Petzval lens based on its focal length?

 

[David A. Goldfarb]

It's something of a matter of taste and planned usage.

Petzvals are mainly used as portrait lenses, so they don't need to cover the format at infinity. If you want the field curvature, you can use a shorter one. If you don't like too much of the "swirly bokeh," then use a longer one.

My 10" Petzval seems like it was made to cover full plate (6.5x8.5"), but I'm planning to use it for portraits on 8x10". It vignettes on 8x10" at infinity.

If I remember correctly, the nominal coverage of a Petzval is on the order of 24 deg.

 

[bobfowler]

Is there a general rule for the coverage of a Petzval lens based on its focal length?

With any lens, you have the circle of illumination and the circle of good definition. With a soft focus lens such as a Petzval, you don't necessarily want the circle of good definition to be as large as would a "regular" lens, rather, you would want take advantage of the fall off of sharpness.

You can expect that "normal" diagonal of film plane focal lengths to have sufficient coverage. I wouldn't advise going with a 2X normal focal length as you'd lose most of the Petzval's charm by only using the lens' sharpest area of illumination. The 10" lens I bought from Jim Galli is perfect for 5X7, though the 10" focal length is "normal" for full plate (6.5 X 8.5 inch). I also have a B&L Rapid Rectilinear of that focal length and the difference on the ground glass is astounding!

 

[jimgalli]

I like 6-8 inch for 4X5, 9-10 inch for 5X7, 11-13 for full plate, 13-16 for 8X10, and 15- ?? for 1114. Of course there's lots of overlap in all of those, that's just general. For instance I wouldn't hesitate to use a 12" on an 8X10 and I've made some lovely things on 5X7 with a 15". I seem to recall they cover about 36 degrees.