On a Canon 600D, what are the best settings for a 4-8sec long exposure in the daytime? I have tried manual and shutter priority modes but photos always come out completely white.
In daylight it is not possible to took such a long pose: the amount of light reaching the sensor is too important: that why your image is "burned" (overexposed full white).
What you could do to reduce the amount of light and incrasse the exposure time without burning the image is
lower the sensitivity (iso) as down as possible,
close the diafragm (pass in aperture mode and rise the f-number as much as possible
but in order to really access long poses the only way is to bought a ND filter: that is a gray filter wich will let pass only a part of the light...
The exact answer will depend a bit on what you're trying to photograph, but if you're trying to do something like a long exposure shot of a waterfall or the like, in general you'll want:
- Base ISO (i.e. ISO 100 for the 600D)
- Aperture in the "sweet spot" for your lens - probably around f/8 to f/11 or so.
- A neutral density filter to cut down the amount of light reaching the sensor
The solution is to use a neutral-density filter to allow you to keep the shutter open longer in daylight without letting in so much light that it ruins the picture. There are a few other questions on this topic that you should check out: