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Aaron,
I don't understand how you come to the conclusion that the mirror is f/4. If the image came to focus at ~1500mm, then that's the focal length, and f/7.5. But this is ONLY an approximation as the actual focal length is determined by the light source being at infinity - having the light source so close and the focal point is shorter! A better way to do this is take the mirror out of the tube (you can wash it at the same time is it's dirty - there's an article about this in the Articles section in the left margin) and do the same thing that you did with a lamp but with the Moon this time. This will give you the true focal length of the mirror.
Yes, a photograph or two will help us with sorting things put.
A laser alone won't allow for true collimation. It won't deal with the secondary mirror! You may think that the secondary is set up properly because of the laser beam is on the primary, but this is actually a false reading. The laser will not tell you if the secondary is properly centered in the focuser nor if it is square with the focuser. This last point is most critical as it needs to be correct before the primary mirror is tweaked. This was a lesson that took me a LONG time to figure out. I too relied entirely on the laser when I first got it, but the "collimated" image was still poor and getting worse until I figured out what the problem was - and unfortunately this part very few people ever mention!
If the mirror had seen better days, then just use this OTA for practice. Cut your teeth with it ith your photography, ad that's all it is good for if the primary isn't in great shape. And if the mirror isn't brilliant, don't do your money on a new focuser as the investment isn't a good one.
We can't really offer much more help unless we know what your gear looks like.
Alex
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