LensRentals has loaned me a Hasselblad XCD 55mm f/2.5 V lens for testing. Today I tested for focus curvature, using Roger Cicala’s test method. I found a flat surface with some texture, set the lens to wide open, focused about 5 meters away, and got this image:
In order to show the in-focus area, I brought the image into Photoshop, and selected Filter>Stylize>Sharpen Edges. That gave me this:
The focal plane of the periphery of the lens is close to the camera than it should be. This is usual. The amount of focus curvature is not bad, but not great.
Hi, I’ve always presumed all lenses has focus curvature with the exception of macro lenses or lenses for enlargers. Is that thinking correct? Thanks.
All lenses have focus curvature. Some lenses have less than others. Macro lenses, enlarging lenses, and industrial process lenses are usually designed to provide flat fields, but no lens is perfect in that regard. These results with the 55V are not unusual.
Thanks for this post. Curiously, does this represent more the lens curvature, or the actual surface curvature? Does the ground truth need to be a little more….planar?
You need an approximately flat surface for this test, with some texture to it. The putting green worked out well.