I am wearing glasses and I have to wear them in the headset, so my options to change the facepad thickness (and comment on it) are limited. What however I can say based on the design:
-
If you set the IPD on the headset to your real life IPD then the lenses optical axes should converge on your eyes, if:
a) Your eyes are at the exactly same spot Pimax used when they calibrated the model,
b) Your headset is correctly calibrated. -
If your eyes are not exactly at the right spot, because either a) or b) above does not hold, you can try to compensate for that by, either:
a) Changing the facepad thickness
b) Changing the IPD set on the headset
Increasing the facepad thickness means you are moving the point of views convergence in front of your face and is roughly equivalent (in terms of the geometric distortion) to decreasing the IPD set on the headset. The same goes in the opposite direction, if you make the facepad thinner, it is roughly equivalent to dialing in bigger IPD.
The relation can be expressed by the formula:
d_ipd = -2 * d_pad * tan(10°) =>
d_ipd = -0,35 * d_pad
where d_ipd is the difference in perceived IPD and d_pad is the difference in the facepad thickness. For example, if you add 10 mm to your facepad thickness, it would make the perceived headset IPD smaller by 3,5 mm.
Because you have two different means to reach the correct convergence point, it means you can also use them to counter each other. I.e. increasing the facepad thickness, while increasing the IPD setting on the headset keeps the perceived IPD the same, but increases the eye distance from the lenses (and vice versa). This principle can be used to fine tune the eye to lens distance, without changing the perceived IPD.
Anyway, what I would suggest is:
- Dial-in the real IPD and see how it goes.
- If not comfortable try some range around the original value, i.e. +/- 2 mm
- If not comfortable, try 1) and 2) with thinner padding (if possible)
- If not comfortable, try 1) and 2) with thicker padding
In general, closer you get the eye to the lens, lesser (geometric) distortion you get. What you suggest (trying the thinner pad first) also makes sense, it is just that with the thinner pad, you may already be too thin.
What is also confusing, Pimax shipping the facepad of different thickness, even though the thickness has direct impact on finding the right IPD. It is as if they did not know, or did not care, but neither is very encouraging.
One thing to keep in mind though, the steps above are supposed to help you primarily with the geometric distortion, but not with getting the sharp image in both eyes. The latter can only be eased by reducing the eye-lens distance, but not completely eliminated. And if you decide to eliminate it by bringing the lenses too close (and ignoring the IPD setting), you will introduce the geometric distortion, which may have some other unwanted consequences.