I recently bought a box of Ektrachrome 100G in 4x5 and specifically looked for reciprocity information before shooting $35 worth of film in 10 easy shots.
As per instructions found inside the box of film I set about last weekend to shoot all 10 shots with a little feather in my cap. I intuited that the information you can read like on this page here: KODAK Reciprocity Info is information not for pinholers but for normal photography. So without so much as a good realistic guide for reciprocity I do what I normally do and that is examine all the reciprocity figures for all the films I have information on, and apply a best average using whatever information I can shoot from the hip. So basically I treated Ektachrome like it was an average of TMAX 100 and FP4 reciprocity exposure figures.
After using my shoot from the hip reciprocity exposure information, if anything the shots should have come out overexposed, but instead they came out underexposed. This is the third time (using three different eras of Ektrachrome) for this mistake for me. Everything is underexposed. Not by much but by enough that makes it difficult to render anything with the scans. And I spent $10 a scan on these so that's $108 down the drain almost. Again. I've repeated this enough times to know that the reciprocity figures supplied by Kodak are just plain wrong for pinholers. I think there's got to be a different way to calculate things for pinhole versus normal lens-photography where you have a lot of light to work with. Anyone with some hints or advice based on experience?