My vote goes for the chimney finder (cds). Well-built, light and accurate. The rotating eyepiece is the dioptre adjustment. Big eyepiece makes it easy(ish) to see the whole image, even when you're wearing specs. If you are going for a metered chimney, just one thing to note: It's a spot meter system. Actually, 'system' is too grand a word for it. It's a metering cell on the end of 'swing-in' arm. A bit Heath Robinson but typically Mamiya. Regards, BLIGHTY.