A focus is a focus no matter what method you use, even if your eyes dont come to complete focus doesnt mean your camera or scope doesnt. If you focus in and out and obtain the clearest image your eye's can resolve then the image will be as sharp as is possible, your eye's may not see it but the device will, camera's included. Dioptic correction at the eyepiece doesnt affect the film plane, in an SLR it is corrected after the focal point of the collecting lens, it is only beneficial for your eye, not the image.