For some odd reason Adobe removed the slider for the Transparency panel some time ago, and replaced it with a mostly useless drop-down menu of 10% increments. While many users certainly aren’t happy about this, they probably don’t know that you can adjust transparency more precisely than the drop-down menu allows using keyboard shortcuts.
With the object(s) you want to adjust selected, click in the Transparency panel’s amount input box and use the following keyboard shortcuts:
- Increase/Decrease Transparency by 1% = Up or Down Arrow Keys
- Increase/Decrease Transparency by 2% = Option + Up or Down Arrow Key
- Increase/Decrease Transparency by 10% = Shift + Up or Down Arrow Key