Transact SQL - Does It Have The Equivalent Of FINDONEOF Function?

Hi All,
Once again I find myself smacking my head into a wall (and it will probably be for naught). I'm trying to find a specific character in a string within a specific record. I've tried substring, but it's not quite getting me where I want to be. I even tried "nesting" the substring and got nowhere (but I could have had the syntax wrong when I nested it).

Here is a sample

Select substring(productimagefile, 20, 5)
from my table

What I need is something like this:

Select substring(findoneof(productimagefile, _r, 1), 1, 5)
from my table

Actually, on the start of the substring, I need it to be where it finds the _r, just not sure how to tell it that.
The replace function is the closest I've seen to what I need, but I don't want to replace it with anything, I just need to find it in the string.

So, if anyone has any ideas, I'd be grateful (and my head would stop hurting....)

Schimelcat