thx guys for your invaluable advise. Guess i will stick to my Tamron.
currently when shooting in indoor with the use of external flash unit, the group photos always turned out pretty dark. Is there something wrong with my settings?
https://docs.google.com/file/d/0B5NSzKFHBTPATEZibDRJUUdEQXM/edit?usp=drive_web
Doesn't really look as if flash was used or there is something wrong with flash settings and flash direction. Why would any other lens help here? :dunno: Anyway, let's have a look at the EXIF.
Portrait Mode: why that? For such conditions the best way to work is Av or M. Learn about exposure, then select the settings. Don't let the camera think for you.
ISO 400: too low for such conditions, use at least ISO 800, manually set.
Evaluative Metering: With this setting the camera will consider the entire area of the image, including some of the lights in background. Use a setting that focuses on the center part of the image. (See manual for options).
Keep in mind to make test shots and adjust the exposure. The bright table cloth will reflect much more light than the people behind, the flash metering will be thrown off by that.
Regarding your Canon 50/1.4: Have you heard about the DoF effects of wide open aperture? Your image reveals this already when you look closely at the faces. With f/2 it will be worse and none of your family members will accept any technical excuse. Because every mobile phone can do it.
I would suggest you read the basics of exposure again (Newbies Corner), use this to learn in daylight. Abandon Portrait Mode and the others, P, Av, Tv and M is what you need to take control.
Read up about the basics of flash photography with Canon:
http://www.photonotes.org/articles/eos-flash/ (Some terms and some things are a bit different than Nikon and other brands.)
Use your manual as well to compare modes and settings.