The focal ratio of a lens is the lens's focal length divided by the diameter of the lens's opening. For a 150mm lens such as the Rodenstock you mentioned, 150mm is the focal length so a focal ratio of f/6.3 (how it's usually written,) means that the largest clear opening of the lens would be about 23.8mm. When the lens is stopped down to f/64, the lens opening would be about 2.3 mm. The practical value of this is knowing that opened to its widest, f/6.3, the lens lets a lot more light through. The image on the ground glass will be relatively bright, making it easier to compose and focus. At f/64 the image will be dimmer because the lens isn't letting very much light through (although depth of field will be greater.) For a view camera, f/6.3 is reasonably bright and should be easy to work with. In terms of quality, the f/6.3 lens was a budget lens, simpler in design and lower in cost than their larger, heavier, and more expensive plasmat designs. It's single-coated (more expensive lenses would be multi-coated,) which are anti-reflection coatings. These coatings reduce glare and increase contrast. Single coating is fine, in my humble opinion, for black and white films; if you shoot a lot of color then you may prefer a more expensive multi-coated lens. I shot for a couple of years with Fuji's version of this lens and was perfectly happy with it. I only sold it because I prefer lenses in other focal lengths.
I can't say much about the Zeiss lens because I don't know much about Hasselblads. I assume, being a Zeiss, that it's a good quality lens (they have a reputation in photographic circles.
A "studio" camera is probably a monorail; seems reasonable and that's what most Toyo cameras were, I think. Monorails aren't as desirable for carrying around out in the world because they don't fold up very compactly and they tend to weigh a bit more than folding cameras. Studio cameras were designed to be rigid as a first priority; folding cameras, generally, are designed to be portable and tend to be less rigid (although these are generalities: exceptions to all cases can be found.) You can carry a monorail around; it's just less convenient than carrying a folding camera in a backpack, that's all. I was once offered a Toyo model C monorail by a fellow at a yard sale; he hadn't heard of the Internet and was unaware of the decimation of prices digital photography had performed and so wanted a laughable price; I just politely declined. It looked like a solid, if perhaps somewhat heavy, camera. I could have made it work, I think, if I had to. I did carry a Calumet CC-400 monorail for a couple of years. The rail was a bit long and tended to get caught on things, so I sawed about 10" off and it was fine from then on. More cumbersome, yes, but also more satisfactory in others. I use a folding wooden field camera now and love it to death but there are times when I miss one or another of the features of the old Calumet.
The condition of this equipment is important and without experience it's going to be hard for you to judge. I'm of fairly easygoing outlook and probably over trusting but I've never been seriously disappointed by a seller yet, thus keeping my disposition sunny and my digestion regular. You say that you've talked to the fellow, he says that he's used it in the recent past and it works and that your instincts aren't setting off any alarms. Speaking personally for myself, that would likely be fine with me. Yes, he could perhaps get more for his stuff peddling it on Ebay but there's effort required in taking pictures and listing it and answering questions and managing the sale. Not to mention packing things so they don't get broken in shipment and finding boxes for everything, carting it to the post office... Then he has to worry about getting ripped off in payment. I think it understandable if he's willing to trade some of the price for a more convenient sale.
Mike
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