# Talk:Petzval field curvature

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Is Petzval field curvature just another way to discuss spherical aberration? neffk (talk) 17:46, 3 January 2011 (UTC)

No, they are completely different. Field curvature is the curvature of what you would generally like to be a plane of focus. That is, field curvature means you can't get the entire image focused at once when focused at infinity or at a flat plane perpendicular to the optical axis. —Ben FrantzDale (talk) 18:04, 3 January 2011 (UTC)

## Equation

I think the equation given in the article is basically right, but I don't think it's fully generic and I also think it's not for the Petzval curvature but for the reciprocal of the Petzval curvature. Please check to see if I'm right about it being the reciprocal and not the actual Petzval curvature itself. Also, I think that the formula assumes that the surrounding medium is vacuum or air. I think that if the medium the optical system is immersed in has an index other than 1 that the formula needs to include an additional factor of n_medium at the front of the equation. This one I haven't confirmed yet. Finally, I think the overall sign is wrong. Please check to see if I wrong. Thanks. 157.185.92.179 (talk) 15:00, 27 June 2012 (UTC)mjd

From dimensional analysis the equation seems the right way up for curvature since it has units of one over distance. —Ben FrantzDale (talk) 18:47, 27 June 2012 (UTC)
Right. I misread the article. The formula represents the *curvature* of the Petzval and the formula uses the *radii of curvature* of the lenses. Most places where I've seen the equation it uses radii on both sides of the equation to avoid confusion. For the article I think that it might be clearer if the equation was turned into an equality with "kappa_petzval =" on the left hand side.157.185.92.179 (talk)mjd —Preceding undated comment added 13:38, 28 June 2012 (UTC)