Orto film and filters

I have bought a box of Ilford Orto Plus 5X4 which I intend to experiment with for general outdoor photography, mainly landscapes and seascapes. One problem I am having is working through the physics of which filters I should use, given the different colour sensitivity of the ortho emulsion. Can anyone advise me? Also, should I be using the same filter factors as for panchromatic film?

Bill

Possibly stating the obvious here, but the below link gives some information about this film and the filter factors:
http://www.ilfordphoto.com/Webfiles/200621611533563.pdf

I should also say that I have no experience using this particular film with filters.

It is a great film, by the way.

A friend of mine always uses a light yellow filter (n°8) when shooting with this film. I have a box of 8x10 wainting in my fridge!

Any of the normal contrast filters (red, yellow, orange) are all blue blockers to a greater or lesser extent. Since the film is essentially red blind, and sensitive to green and blue, the response you'll get by using these filters will be radically different from the response you'd get with a panchromatic film. If you expect to separate clouds and sky, that's not going to work so well. Filter factors for these common filters are higher than you'd expect. Normally, a light yellow filter costs you about 1/2 to 1 stop of light with panchromatic film. With OrthoPlus, you need to allow more than 2 stops. Film speed under tungsten light is dramatically lower (half) as well because tungsten light is rich in red, but not so much in green and blue.