findDQE use

Hi,

I am doing some things that involve running findDQE on several cameras and have a question. The J Str Bio paper says that the program can work on a pair of images and use them to estimate the noise power spectrum. I have assumed that this means a pair of images with the beam stop in place, but that's not totally clear. I have not yet tried this option with findDQE but I collected images that I think I can use.

Maybe I am being dense, but it's not clear how to tell findDQE that there is a pair of beam stop images. I know that one of the questions for input is the number images, but the prompt implies that a second image should be a flat field/gain reference image, which to me is different from a second beam stop image. Is the prompt wrong about the second image? Alternatively, is the paper not clear that the "pair of images" it refers to are really a blank field with and without the beam stop?

I would just run the program and use one of the image pairs I have, but I'm not sure there is output that would tell me that my second image was what the program expected or not, and thus I wouldn't be able to tell if the output was really meaningful or not.