Service Question: getting AF and split prism focus screen to play "nice"

D90 is 3+ years old. camera was showing rear focus behavior based on lots of careful tripod mounted test shots, several pros looking at test shots, service shop testing, etc.

found that I could get very accurate manual focus using split prism focus screen.

testing using nikor AF-S 35mm, shots at F1.8, variable speeds faster than 1/100, distance of ~1.5 ft, AF in single point ( center ) mode, natural light, remote triggered shutter

in addition to finding that AF put focus in test images behind the focus point, noticed that AF focused lens appeared "off" based on visible misalignment of focus point in split prism.

so i took the camera for AF service, to a reputable chicago based repair business providing service for customers throughout the US. the initial repair resulted in front focus shots. took the camera back for no-charge re-repair.

AF is perfect! now, images focused manually using the split prism focus screen are not in focus. as i write this i'm embarrassed to realize i don't know if they are front or rear focused, but most importantly the manual focus using split prism is no longer is accurate.

QUESTIONS:

is there a likely reason why correcting the AF behavior of the camera would cause the manual use of the split prism to no longer be accurate?

does the focus screen impact the AF behavior in any way?

is there any inherent problem with getting AF and split screen focus to agree?

i am planning to follow up with the split prism focus mfr to ask these same questions of them.

thanks in advance.

Re: Service Question: getting AF and split prism focus screen to play "nice"

you may have slightly misaligned the mirror when installing the screen.

Re: Service Question: getting AF and split prism focus screen to play "nice"

OK, so you have 3 focus modes...

1. Live view
No mirrors are used and no setting up is required, just focus lens onto the sensor as it's seen in live view.

2. Viewfinder, Manual focussing.
The front mirror must be set so when the image is focused, you press the shutter. The mirror then raises and if the front mirror was set correctly, the same focussed image will now be on the sensor.

3. Viewfinder Autofocus.
The rear mirror must be set so when the image is in focus on the AF sensor, it gives the same focus to sensor plane when the mirror is lifted.

>>CLICK HERE<< for more information, and a picture that will help you understand the 3 focusing modes of your camera.

The adjusters are 2mm allen grubs, inside the body, you can see them when the lens is removed and the mirror is raised.
Best left to the professional if you don't know which is which or what way they need to be turned to correct back or front focussing issues.

EDIT: Just noticed the page says the grub screws are 1.5mm, pretty sure mine was 2mm but not 100% certain.