I often use a highpass filter in photos and use various blending modes in layers while doing photo work or purely digital images.  Yet, I have yet to figure the real differences when using "blend" modes in **Opacity** and **Fill**.   Used one at a time the effect seems about the same. Used together, I think I see some difference but am not sure.

Is there a simple way to know which to use or how?  Any input will be greatly appreciated.

TomDart.