those would be called "speed easels". speed-ez used to be a popular brand. the manufacturer, saunders, makes a nicer version of these, with a hinged frame (3/16th or so border all around) in a preset size. There's a 5x7 Saunders model with a removable bar that sits off-center. You can leave this in place and get a 3.5x5 and 4x5. Pop it out, get a 5x7. The speed-ez's, come in all sorts of sizes from wallet up through 20x24. They're yellow--slide the paper in either side. These can be kind of cheaply made--they get warped pretty easily, don't hold the paper flat all the time, and they can be hard to get the paper centered accurately for an even border. But they're cheap....
Originally Posted by Huram
a "4-in-one" easel might be worth looking at--premier, kalt, costar etc all make these. you get a preset 2x3, 3x5, 5x7 and 8x10 on the back. These are pretty cheap too, and you oughta be able to find a used one easily.
btw-I do have an Omega handbook from the late 50s, that covers some of these earlier ones & has all the condenser set info, plus the various lens board dimensions etc. I think you can pretty much use the D2 instructions though--the two models are slightly different, but it's a pretty easy beast to learn how to use.