It is fair to say that there are differences between these two designs.
Over the last decades, R&D has been focused on improving roof binoculars. Resulting in ever better models. And some surprisingly good affordable models in the US $ 300-400 range. Internal focusing and waterproofing have become the norm in roofs, as have the adjustable eyecups. Generally they focus quite close, in the 2-4m range.
Downsides of the design? Limited depth of field, sensitivity to spikes on bright lights and the necessity to apply both phase correction and highly reflective coatings on a roof prism surface. And they are MUCH more sensitive to alignment of their prisms, further increasing the cost to make them well. In exchange you get a sleek form format, generally well suited for eyeglass wearers. As an added bonus, fields of view get sharper to the edge and wider by the decade.
Porro’s have there own advantages by design, but are not currently developed any further, in stark contrast to roofs. To their advantage, their designs have wider optical bases, hence much better depth perception in the images at close- and mid range. And no spikes on bright lighthsources, because porro’s don’t introduce them to the image, as roofs easily do where they split the incoming lightbeam. Only the very best have (almost) no visible spikes on bright points of light. Eyepiece designs and instrument designs have come to a hold decades ago. So they tend to represent the design philosofies of decades ago. But some of them are still valid AND outstanding, like Swarovski Habichts, Nikon’s EII, Prostar and Astrolux make clear to their users every day AND night. But they are not easily adaptable to glass-wearers., have fixed or fold-down eyecups and generally have smaller and less wide fields than current roofs. Waterproofing is different too and certainly not as common as with their roof counterparts.
The very best roofs have come a long way in narrowing the optical gap with porro’s on-axis, with many additional features to boot.
I have owned the best of both designs and found them both to be wonderful, yet different by nature. I still own some of the best of both and could not do without either of them. They are not interchangeable, but excel in different ways. Just choose were the focus of your personal use-cases are. And be prepared to pay double to triple the price for similar on-axis quality.
The best example from the same manufacturer making similar magnification and aperture roof and porro binocular models currently being Swarovski. That makes a fair comparison of similar production quality easier. The roof NL 10x42 and porro Habicht 10x40. US $ 3000 vs US $ 1000. For comparable on-axis performance, but vastly different form factors and off-axis performance. Not to mention the night and day difference for eyeglass wearers, field of view and haptics. But the images and user experience for both is outstanding. Just different.
