Can I have both Lightroom 3 and Lightroom 5 both installed on the same computer? I like the "fill light" feature in 3 and use it a lot. I would have not gotten 5 except that the images from my new Canon 5D Mk III are not re4cognized on 3. I have 5 on a laptop and 3 on my desktop but would like to have both on my desktop .
Yes you can do this, but you can also get rid of Lightroom 3 and use the "Fill Light" command in Lightroom 5. You need to set the Process Version to 2010 (default is 2012 in Lightroom 5). Use the menu command Settings > Process > 2010
But honestly, you would be wise to stop using "Fill Light", as the new sliders in Lightroom 5 produce superior image quality than anything you can come up with using "Fill Light". Yes, the new sliders take a little time to get used to, but your patience and effort learning the new sliders will be rewarded. You can find some tutorials and videos on using Process Version 2012 on that Internet thing.