Masking different tones in Photoshop

I need some help.

If I want, for example, apply some adjustment more strongly on bright tones and less on dark tones, I would create adjustment layer and paste contents of background layer into adjustment layer mask. If I want more strong effect on dark tones and less strong on bright tones I would just invert mask.

But... what if I want to apply strongest adjustment on mid tones and fade away effect on both sides of histogram - fade it for dark and for bright tones? How to create mask for that? So, the mask has to be almost white over mid tones and dark over brightest and over darkest tones from original layer.

Thanks

If it mustn't be a mask, use the "blend if" sliders (double click the layer or select "layer properties" from the layer palette flyout menu)
Move both sliders, alt-drag to split for a softer transition.

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Rene, first approach works great! Thanks.