Mouselook
Mouselook, allows you to see Second Life from a 1st-person perspective — "through your avatar's eyes". The keyboard is still used to move your avatar, but your mouse, as the name suggests, is used to look around.
To enter Mouselook, go to View menu > Mouselook or simply press M when the chat bar is closed or doesn't have focus (otherwise, you'll type an "M" in the chat bar). Instantly, the camera zooms into your avatar's perspective.
To leave Mouselook, press Esc.
Show/hide your avatar in Mouselook
You can toggle whether or not you see your avatar in Mouselook. Showing is useful if you want to feel a closer connection with your avatar, but if you're filming video and don't want your parts (depending on your avatar's size and attachments) to interfere, you can also hide your avatar.
- Go to Edit > Preferences.
- Click Input & Camera tab.
- Next to Avatar Display Options, either check or uncheck Show Avatar in Mouselook.
- Click OK button.
Go into Mouselook and see if you notice the difference, as shown in this video:
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Mouselook options
Go to Edit > Preferences. Click Input & Camera tab and look next to Mouselook Options:
- Mouse Sensitivity - Adjusts how touchy your mouse is to motion in Mouselook. Moving the slider towards the right increases sensitivity, meaning a slight jerk of your mouse in Mouselook will make shift your view further then if the slider was on the left.
- Invert Mouse - Enabling this means Mouselook motions will be opposite to your mouse's actual movement. For example, if you move your mouse up, your avatar will look down. This can be preferred behavior when in some types of Mouselook-piloted vehicles, like aircraft.
In the unsupported Advanced menu, there's a Mouse Smoothing option. Enabling this evens out the Mouselook acceleration curve so sudden motions appear more gradual.
All of these options are shown in this video:
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Caveat
Mouselook can be a great way to gain additional immersion, but many parts of the user interface can't be accessed in Mouselook. For example, you can't build, nor can you sort your inventory. It's possible to open certain controls such as the Communicate window when in Mouselook, but since your mouse is controlling your avatar's viewpoint and not the regular cursor, you can't capably interact with them.