I just got a Yn685 hoping to be able to focus better in low light. However, the red grid that is projected is WAY out of alignment with my focus points (Canon 6D). Is there anything that can be done about this? It seems completely useless if the grid isn't aligned with the center focus point (and indeed does not seem to help achieve focus).
Anything I can do?
This is an apparent design flaw.
The YN685 is a very inexpensive superficial copy of the Canon 600EX. I wouldn't call it a "clone" as that implies more similarity than actually exists.
The Canon 600EX (and prior flashes such as the 580 and 580-II) project a pattern of horizontal bars that provides a good target for the camera focusing mechanism. The YN685's laser grid looks really cool, but is mostly useless as a focus assist beam.
Due to parallax effects, no matter how well aligned it is that alignment applies only at a specific zoom setting and subject distance. As you change the zoom and/or move towards and away from the subject the position of the grid lines will unavoidably change, and it's hit or miss whether or not they fall near focus points. That part is basic optics. The flaw is the use of a fine laser grid.
You must accept that since the YN685 costs ¼ the price of a 600EX, you are getting about ¼ the value.
It does have other issues. It produces incorrect exposures in certain situations using bounce mode and ETTL (it requires evaluative metering; See this question) and the zoom motor is very noisy whereas the 600EX is almost totally silent.
I tried two copies of the YN685 before finally biting the bullet and springing for the 600EX. I think Canon's flash is somewhat overpriced, but it does what I need and does it well. It all comes down to "you get what you pay for".
It seems completely useless if the grid isn't aligned with the center focus point
Well, I hope the misalignment is not to the sides. If it is poining up take a look at this: http://www.dpreview.com/forums/post/54160864
This depends on the focal length you are using. The misalignment would be more on a longer lens.
If the beams were pointing down, they would depend on the distance to your subject.
One posible solution is that you do not tight the screw so your flash has some free movement. Just take care of not droping your flash.
One DiY "hack" could be putting some small layers of transparent sticky tape to form some refraction on the beam and spreading it a bit more.
One option is to use it on another focus point and reframe.
If you are using a zoom lens and the focus does not change when zooming in, focus on a longer distance and re-zoom.
