http://www.antiquecameras.net/1890lenscatalogue.html
See page 7. It covers 14x17 wide open and 18x22 with a smaller stop. I suspect it would cover 20x24 with a small stop. It's a 21.3" (542mm) lens and does throw a large sharp image circle. Though keep in mind that a rapid aplanat like this will have quite a bit of field curvature wide open. It does flatten as you use smaller stops.
I think you should be thinking more about focal lengths for the type of portraits and landscapes you want to shoot. Generally, portraits are more flattering when shot with a lens slightly longer then the standard focal length. I also have a Euryscop IV No. 6. Which I bought with slightly wide 12x20 landscapes and 12x15 portraits in mind.
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