Like said above your post, there's an official thread for OBGE issues, and it sounds like you're stacking DoF shaders?? They don't "switch" because nothing is as of yet released to toggle shaders. However, like being discussed in the current OBGE thread, I'm writing two mods, one to dynamically control DoF and the other to control SSAO. I have a bow-aiming-specific DoF toggle already coded in my mod.
In the meantime I would suggest NOT to use multiple DoF shaders, it's already not advised to do. Applying multiple DoFs will harm performance with each shader applied.
Bokeh and the Crysis DOF shader work together like a charm.
Bokeh offers no distant blur, but Crysis DoF does, and together they work 95% of time perfectly.
In case of those 5% I have to reload, or restart.
Its absolutely irritating to have Bokehs blur in 3rd person, and when switching to 1st person, its only nearblur.
adding the crysis DOF gives a neat distant blur even in 1st person, if you adjust the values of both, they work seamlessly together,
and you wont notice that its two different shaders working at the same time.
But back to the bow, i was wrong about saying that the combination of the two DOF shaders will prevent a near focus when the actor does aim with the bow in 1st person.
It seems to be fully dependent on the Arrow, some arrows dont cross the focus point, others do. then it wont focus near, and you will have to aim at a blurred target in the distance.
To avoid to much blurring, I have set the R value to 4 in Bokehs shader, and the radius to between 0.7 and 1 (whether hexa or circle version of bokehs).
The value of the crysis dof are more subtle to find, the distant blur has to be true, and the other values have to be adjust while being in 1st person mode. I think its mainly two values,
one for the distant blur strength, and one for the seamless blurring from near to far.
With this settings, the distant never blurs this much as with default settings, and you are able to aim at distant targets. Especially Bokehs uses very extrem default values.
Here are exmaples pictures in highres quality to see:
http://img600.imageshack.us/img600/1319/oblivion201101270934096.jpg shows 3rd person near and far blur:
http://img263.imageshack.us/img263/5720/oblivion201101270934171.jpg shows 1st person near and far blur.
http://img819.imageshack.us/img819/4575/oblivion201101270935006.jpg shows 1st person aiming with iron arrow and correct blurring.
http://img577.imageshack.us/img577/6018/oblivion201101270936029.jpg show aiming with a different arrow and not blurring correctly.