I have an iMac 21.5 and still running Mountain Lion. I am also still using LR 4 and trying to find out the compatibility on EL Capitan. Any Advise?
Lightroom 4 has not been tested on Mac El Compatibility and we have not been reported any major issues till now.
So, you might want to update and check if it works well.
Your sliders might not be the right color. See here.
Sliders in Lightroom 5 are white, blue, or look different in Mac OS X 10.9, 10.10.
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