Easiest way is to place the Fresnel on top of the gg so it is on the
side that faces your eye. This makes no change in focus plane, can use
any thickness Fresnel and the fresnel can easily be removed when you
don't want to use it. This is where Linhof, Wista and Sinar place their
Fresnel screen.

Yes, the fresnel is definitely brighter with the f8 90mm SA, but I removed
it and reinstalled my plain ground glass.  The fresnel lines get in my
way of focusing.  Ultimately a Maxwell screen would give me the best of
both worlds, but I haven't forked over the $200+ for it.

Many thanks for that piece of info.  It's arrived at a good time.
I'm going into London on Saturday, and will almost visit a few photo shops
where I may find a screen, and I'm certainly not taking my MPP or lenses
with me!

Things are going to be pretty dim just because of the f8
aperture.  Compare the SA to your regular lens @f8 - there
may not be all that much difference due solely to the
focal length.

And then there are three locations for the fresnel:

o in front of the GG, as in the Speed Graphic;

o molded into the GG, as in a 35mm SLR;

o in back of the GG, as in Sinar.

Not quite sure how this interacts with the lens FL.  The
Sinar GG is useless with a 65mm, but works OK with 90mm and
up.

If you are adding/removing the fresnel at the front of the
GG you have to reset the location of the GG.  I don't know
how the MPP mounts the fresnel.

I use a micro-fine GG in 35mm and the standard GG with a
reflex hood with the Sinar.  If you can exclude most of
the ambient light I think a plain -very fine- ground glass
gives the best overall performance.

The Speed Graphic with the normal lens and the front-mounted
ground glass has a very acceptable image using just the
flip-up hood.

"Satin Snow" ground glass gives a very bright image and
has a loyal following here in the US, though manufacturing/
delivery has been erratic.

My Wista DX came with a fresnel lens already laminated to the
groundglass.  In that form, it is not a problem with a 90mm lens, though
I begin to see some difficulty in the corners especially, with a 65mm
lens.  My guess is that with a 90, you'll be OK.