Posted By Dan D DuBal
I recommend a simple meniscus shield/baffle sleeve (like a dew shield on a refractor). Cardboard, craft foam, felt-lined bubble-wrap -- these materials are fine. Make sure the interior of the shield is flat black (not glossy or shiny or otherwise reflective). The sleeve/shield should project a distance equivalent to at least 1.5x the scope's aperture (up to 2x is also fine -- do not make it much longer). This would mean about 5 to 7 inches for your Apex 90.
All cassegrain designs require some level of compromise with regard to the length and/or shape of the primary baffle tube. If a primary baffle tube is made long enough to strictly/fully baffle the meniscus, then it will end up projecting into the primary light cone, thus *increasing* the effective diameter of the central obstruction. On the other hand, if a baffle tube is made short enough to allow for *zero* additional obstruction, then the meniscus ends up *not* being fully baffled.
A forward shield/sleeve/extension baffle should help quite a bit.