If you're having issues finding perfect focus...this might be why. How to test and adjust your secondary mirror.
New to Astrophotography? Need help with PHD2 autoguiding? This Star Stuff Video Series episode has some great tips on PHD2 setup and troubleshooting.
Think BackyardEOS and BackyardNIKON with PhD Guiding, without the need for a separate computer, simplified, and in a slick anodized red metal housing.