I understand your desire for an SEI photometer. I have one that I bought new in '66 at the first of several AA workshops I attended. The 1/2-degree spot is really nice, particularly if you need to read just the full moon. It's still going strong with the original bulb. But it did require a bit of heady mathematical gymnastics to use which became easier after practice. Like AA, I use it simply to find the luminance in c/ft^2 (which is the reciprocal of the shutter speed); the square root of the box speed represents the f-stop. That establishes Zone V; visualization adjustments follow from there. Heckuva meter.