I'm looking for a good used 210mm lens. Use will be with a 4x5 Omega, mostly arc hitectural subjects, black and white mostly but do use some color and will do mo re in the future. Is the 210mmf6.1 Xenar a good lens for the application? I'm co ncerned with some reports of the Xenars having field curvature which can be an i ssue with geometric subjects. Is this a multi-coated lens? Any other recommendat ions on a 210? I would like to spend less than $500 is possible.