Hi folks
I've got a hankering for a Petzval to shoot head and shoulder portraits on 5x7, but have no idea how long the focal length would need to be. I read that only about 30 degrees of the coverage is sharp, but how big is the overall coverage?
You see, I think if the eyes are sharp, then the rest can be as soft and funky as it wants to be.
So if we assume the width of the eyes will not be more than 3 inches on the negative, how do I work out what length Petzval will be suitable? Vignetting of corners is not a problem and I don't care if the outer area is really swirly.
If my maths is correct, to cover a 3 inch circle with a 30 degrees lens, you would need a focal length of 5.6 inches. However, what would the diameter of the illuminated circle be for a 5.5" to 6" Petzval? Would it be big enough to illuminate 5x7?
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