Dick,
It looks like this setup has picked up more detail than the 250 alone
Not sure what you are after...higher magnifications or more "detail" (resolution?) at a given magnification.
Your Raynox DCR250 is a +8 diopter (125mm focal length). The 50mm lens is essentially a +20 diopter. So what you are doing here is "stacking" them together. You will get higher magnifications than either used alone, but it is not surprising to experience image problems.
In an endeavor like this it is hard to predict what will work well together, so experimenting the way you are is important. But it is probably generally safe to say that the results obtained from stacking disparate optics on the front will not provide results of the same quality as a single quality close-up lens used alone. So, for example, I would use the Raynox DCR250 alone, and increase the focal length of the Canon lens until I achieved the maximum possible magnification. Then , if more magnification was needed, go to a (single) higher "diopter" (shorter focal length) close-up lens on the front...perhaps something like your 50mm lens. I would only resort to stacking pieces together when the magnification needed was greater than could be achieved with a single piece on front.
