Secondary Mirror Size and Low Power EPs

I'm anticipating being able to use my Discovery 8" F6 PDHQ soon (Thanks again A-marters!). With 1.52" (38mm) secondary, am I foolish to use a 36mm 70deg EP (H.S. OBS)? What is the upper limit of TFOV/ field stop that I can expect to get/use with this scope?

I have heard people talk about % illumination before, but so far don't understand it very well. If that concept is involved here, can you please be fairly explanatory?

Thank you to all from a refractor refugee!

The initial title sounded like a cliche' which EP post- so I tried to make the title more relevant to my question. Thanks!

The illumination depends on the distance between the
secondary mirror and focal plane, which I do not know
for your telescope.

But I would not say that you are foolish for trying
wide eyepieces. The eye is not very sensitive to
smooth light fall-off, so you may not notice any
problems.

Percent illumination refers to the fraction of the
primary mirror area that is being utilized at each
point in the focal plane. 100% means the entire
primary mirror area is being used. 50% means only
half the primary mirror is being used.

The diameter of the focal plane region with 100%
illumination is given roughly by d-(S/R), where
d is the secondary mirror clear diameter, S is
the distance from the secondary to the focal plane,
and R is the focal ratio.

For your scope we have 1.52-(S/6), but I do not
know S for your scope. Maybe if the secodary holder
covers the edge of the secondary mirror, a number
slightly less than 1.52" should be used for d. I will
assume the secondary holder lip is 0.05". Probably
8" is a reasonable guess for S. So we might have
1.42-(8/6)=0.09". But you should really re-work with
some measured numbers.

The 50% illumination area has roughly the same diameter
as the secondary mirror clear diameter. So for your
scope it is about 1.52" diameter.