Also, rub your hands together to generate warmth. Then hold your hands over your eyes so that the warmth can relax the eyes.
Keep the eyes relaxed, blink freely - whenever you feel the need. One of the basic keys to the whole system, and to accelerative learning in general, is to relax. Ideally, I think, there should be zero eyestrain in the process of PhotoReading and any strain that occurs in the early stages is due not to the PhotoFocus state itself, but is due to trying to hard to get the state. Once more, relax the gaze. If you see the blip page, great. If not - no big deal. If the words are blurred, that's okay. If they are clear, fine. The idea is not to deliberately defocus the eyes, nor to cross them. Instead, just gaze and take in both pages at the same time. The PhotoReading book gives several alternative techniques for using the eyes while PhotoReading. Play with them all.
Anyway, about photoreading making your eyes sore, I had the same problem initially. I think what you are doing is that you are trying to force your eyes at the same time to focus on the pages and beyond the pages. There is a confclict there and it makes your eyes sore (eye muscles). Forget focusing on the actual pages. Try for example to hold the book on your lap. First look at your feet and keep your focus there. Then move the book in front of your field of view and see if you try to focus on the pages or beyond them. Once you get the knack of focusing beyond the book your eyes can take endless hours of photofocus without any strain. In the end I can see the words clearly (even though of course I don't read them) and the blip page. It's kind of weird, you don't have that effect in other things in life in my opinion.