SFX200 is sensitive to light up to 740nm.

The Hoya R72 blocks all wavelengths up to 720nm.

So, first and foremost, you need to be aware that you are photographing a range that you can't see and your camera can't meter - and it's a very slim range at that.

Ilford's Tech Info recommends increasing the exposure by 4 stops over what your meter would say when the filter is off.

But, that's not quite the whole story. If your shutter speeds are starting to get long, you may have to also account for reciprocity failure. Ilford lists a correctional factor of exposure^1.43.

But, also consider that IR light is both absorbed and reflected differently than visible light. For example, it gets absorbed by water and scattered and reflected by foliage. You'll have to keep this in mind, especially when it comes to shadow detail.

So, the reality is: taking a meter reading and then adjusting by 4 stops will be your baseline. You'd be wise to bracket your shots.

---

Sidenote: Also be aware that IR focuses differently as well. Lenses typically have an IR adjustment line/lines/dot. You'll need to obtain focus and then minutely move the focus using the IR guide.