![Quote](images/misc/quote_icon.png)
Originally Posted by
Mike in NY
Since your son said, "assuming they are set at the same f stop," did you assume the opening for an f/8 Waterhouse stop for a Petzval lens would be larger than the opening of an iris stopped down to f/8 on the small RR lens? That wouldn't be the case. To build on what Emmanuel said, the reason the Petzval lens is so much bigger than the RR lens is because its maximum aperture is so much larger. The two lenses "start" with different apertures. If you built an RR lens with the same maximum aperture as the Petzval, it would become a much bigger lens.
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