From a seminarian reader:
My present church is thinking on having a EF Mass as well as a Versus Deus [Deum] OF Mass. The Original High Altar is still in place with the Tabernacle.
There is however a smaller “fixed” “table” Altar in place a few feet in front of this. The “table” Altar is too small too accommodate a EF Mass. Is is still O.K. to celebrate a Mass in the OF & EF with the Old High Altar, while disregarding the “table” Altar.
It is always good idea to ignore iron-board altars whenever the main altar is still there and still usable. The next step is to get rid of the interloper-altar and use the original main-altar exclusively, as was intended in the church’s design.
There was never a directive that table altars were to be set up in front of main altars or that main altars were to be abandoned or destroyed.
Furthermore, in an issue of the Congregation for Divine Worship’s official publication Notitiae in May 1993 there was some years ago an editorial article which stated:
The principle of the unicity of the altar is theologically more important than the practice of celebrating facing the people.
Clearly the main altar was intended to be the focus in the design of the church. It is absurd to put up another altar, within the sanctuary, in front of the original altar.
But, yes, it is always appropriate to use the original, main altar of a church for either the Extraordinary or Ordinary Form.
As a matter of fact, celebration ad orientem is the way assumed in the rubrics of the Ordinary Form. For example, in GIRM 154 we read that the priest turns to the people if he is going to use the option of inviting the people to make a sign of peace. thus: “… extendens et iungens manus, pacem annuntiat, versus ad populum, dicens… opening and then joining his hands he announces ‘peace’, having turned toward the people, saying…“.
Finally, as a seminarian, you should run, not walk, to get yourself your very own copy of Joseph Ratzinger’s The Spirit of the Liturgy. In this useful book, the future Pope lays out the theological significance of ad orientem worship. You will want to study this section carefully and commit it to memory. I have a few PODCAzTs on Ratzinger’s view.