'07 Cayman 2.7 w/ factory halogens. I'm not convinced my
headlights
are set properly. "headlight adjustment" showed up on my carfax during a big service visit. I've been spending a lot of time with them because I actually broke my high beam reflector while seating some new H9's(Hoen hyper yellow). I have the high beam reflector repaired but have also just installed a Morimoto HID kit for the H7 low beams. I have read the owners manual for height adjustment but after not being real happy with the results, I started playing with the focus. I have them pretty good now and can see they're good for oncoming traffic also. My question is just how do you properly adjust the focus which moves the beam up and down just as the height adjustment? For those who may not know, the up and down described in the manual is behind the little hinged flap on the inner fender well and requires a long 5mm allen wrench. It moves the whole assembly up and down. The upper access cover on the inner fender well which is not hinged uses the same wrench and moves the projector lens fore and aft. This fore and aft movement results in the cutoff moving up and down. There must be a merger of these two adjustments that I'm not seeing. I know someone is going to want me to take it to the stealer but I would rather learn more myself before I resort to that. Thanks, C.
'07 Cayman w/ halogens. I mapped my lights on the wall. The top screw does in fact move the beam up and down as the projector lens runs fore and aft but it looks like it also makes a more subtle side to side move. I assume you would make the lateral adjustment first then make the final vertical adjustment. My lateral was right on. What threw me was seeing the lens move forward and backward. After looking at several diagrams, I see how the lens and "shutter" could have a relationship where in and out of the lens would result in side to side of the beam, or more specifically the cutoff notch. It would be the angle changing between the cutoff on the shutter and the lens. Can anyone confirm this for me? Thanks, C.
There's a nice article on Wikipedia about automobile headlamp design that includes schematics of low- and high-beam illumination patterns, as well as projector headlamp optics. (See here:
Headlamp - Wikipedia, the free encyclopedia
)
Following are some additional details of the behavior of the projector headlamp optics and adjustments of the lens, which answers your question and agrees with your intuition:
If the optical axis of the lens and the optical axis of the reflector are coincident, then moving the lens forward or rearward along the optical axis moves the focal point of the lens relative to the focal point of the reflector and thereby changes the degree of collimation (angular spread) of the beam, which serves to adjust the width of the illumination pattern. As the optical axes are assumed to be aligned, such an adjustment does not steer the beam as the beam is broadened or narrowed.
If the optical axis of the lens and the optical axis of the reflector are parallel, but are displaced – such as caused intentionally by using the horizontal or vertical adjustments of the lens, then the beam will be steered left or right, or up or down. Such an adjustment should not change the degree of collimation of the beam, but will affect the illumination pattern on the roadway.
Depending on where the shutter/shield and its notch are placed (not user adjustable) relative to the focal plane of the reflector and the optical axis, the effect of adjusting the lens along the optical axis could cause the illumination edge produced by the notch to move transversely as the beam also widens or narrows. This could happen even if the optical axes of the lens and reflector are coincident.
Here’s one possibility for a sequence of adjustments of the low beams (assuming the car and a suitable target have been prepared and positioned as described in the Owner’s Manual):
1) Covering one lamp at a time, adjust the beam from the uncovered lamp to set the height to specification, as observed by the vertical cutoff. Repeat for the other lamp.
2) Covering one lamp at a time, adjust the beam from the uncovered lamp to set the horizontal displacement of the center of the beam (not necessarily the same as the location of the notch) to specification. Repeat for the other lamp.
3) Covering one lamp at a time, check the width and placement of the illumination pattern on the roadway, such as at distances indicated in the Wikipedia article. Only adjust the foci (forward/rearward adjustment) of the lenses as a last resort to adjust the widths of the beams.
4) Repeat 1-3 to check directions, widths of beams, and illumination pattern.
Note, accurate assessment of the illumination pattern will require an optical power measurement (eg. using a detector that can be moved traversely in a plane normal to the direction the car is facing), as absolute differences are difficult to assess by eye.
