...as you mentioned perhaps it will be of interest to few, but for the sake of precision I believe it's worth mentioning - and about angle of view being larger with the lens focussed close.
Just to be clear, it's the image circle which increases in diameter (becomes larger) as you focus closer and not the angle of view. The increase in image circle diameter at closer focus distances would be true of any lens like the current Phase One XT lenses which have a low-tech focusing system that simply moves the entire lens assembly forward and backward and as a result the spacing between lens elements and groups never change. It's the inverse square law at work projecting an increasingly larger cone of light as the distance between the lens and image plane increases with closer subject distance. With a more complex lens design having floating lens elements or a change in spacing of lens groups as you focus, the relationship becomes less straightforward.
Again, thanks for the interesting article and for providing in it some of the specifications and lens data which I don't see published by Phase One. Perhaps it's just me that's frustrated by the lack of lens data from manufacturers and distributors.
Few manufacturers offer a reasonably complete set of lens data and it requires you to go hunting it down across the internet,
if you can find it there. The
specifications provided by Phase One are minimal at best. On their web page you get "angle of view" and the
nominal focal length (23 mm), but not the
actual lens design focal length standard for which the the lenses are produced which is 23.82 mm per Alpa. If you click on "Download Technical Specs Sheet" you can then find the image circle diameter. No information is given for what the actual "angle of view" is relative to sensor size. For focusing the only specification is "ultra fine manual focus", but no information on how close you can focus or maximum image scale.
Rodenstock, Alpa, and Sinar have identical minimum focus specifications for each of the HR lenses (0.25 m for the HR 23 mm). I don't know, but I would not be surprised if they all share the same focusing mount offered by Rodenstock rather than reinvent a wheel (or focusing mount) that already exists. Cambo Rodenstock X-Shutter lenses have slightly different minimum focus specs from the other three mentioned, some shorter and some longer. I have no idea what the minimum focus distance is for any of the Phase One XT lenses and I've searched pretty extensively. None of the Rodenstock HR distributors appear to give the lens entrance pupil which would be helpful to know, if you do panoramas, for determining positioning and to find the right shift plate length for a given lens.
By piecing together lens data from
Rodenstock,
Alpa,
Sinar,
Cambo, and
Horseman—which sell Rodenstock HR Digaron lenses in focusing mounts—you can get a more complete set of specifications to assess the capabilities and the limitations. Rodenstock provides MTF data and other optical specifications, including shift range for various sensor sizes. Alpa provides accurate focal length data which they refer to as "effective focal length". Sinar gives recommendations for minimum, maximum, and optimum scales of reproduction which produce a minimum resolution specification. Horseman states that the HR 23 mm is 15 Elements in 11 Groups.
If you have a precise focal length and sensor size, you can accurately calculate things like angle of view; field of view; and image/reproduction scale (magnification at a given distance). There are handy online calculators
like this which will do the math for you. The results are very precise at infinity and long distances. They are generally fairly accurate approximations at closer distances, depending on specific lens design and image scale. If you want to know the data for a specific image circle diagonal rather than a sensor size, you can enter a sensor size of: 42 x 56 mm for a 70 mm diagonal image circle; 54 x 72 mm for a 90 mm diagonal image circle; 60 x 80 mm for a 100 mm diagonal image circle; or 72 x 96 mm for a 120 mm diagonal image circle. You can then compare angle of view for various sensor sizes relative to image circle.
