I am actually surprised that you get overexposure for a beach scene. Normally you would be more likely to get underexposure. There are a number of reasons that spring to mind which explain why you might get overexposure....
- exposure compensation set incorrectly;
- poor choice of metering mode such as spot or partial and improper use of such modes;
- predominance of dark areas within the scene, especially in the metered zone(s)
- using evaluative metering and placing the active focus point on a dark subject.
but there is little point guessing at the cause of your problem. It really would help us understand what's going on if you can post a sample picture with EXIF intact, just like my example below.
This was shot using Av mode before I knew of things such as Sunny 16. Exposure compensation was set to zero and I used evaluative metering. I picked f/8 and 100 ISO and the camera picked a shutter speed of 1/800. That exposure is equivalent to Sunny 16 minus 1 stop. This has had no edits and I think the exposure looks a tiny bit dark, but very useable. That said, it can take another 1/2 stop added to the exposure in Lightroom without blowing anything (even the white teeshirt) or looking overexposed.
| HTTP response: 404 | MIME changed to 'image/png' | Byte size: ZERO |
Knowing what I know now, I would have shot this with a manual exposure, starting with a standard Sunny 16 setting of f/8, 100 ISO, 1/400 and then checking the histogram and adjusting as necessary to avoid clipped highlights. That would probably have resulted in a final exposure of f/8, 100 ISO, 1/500, equivalent to an exposure of Sunny 16 minus 1/3 stop. That exposure would have continued to serve me well for any number of shots in those lighting conditions (bright front lighting from direct sunlight) for the next hour or so.
Here is another photo shot on the same day but 1 3/4 hours later. The exposure for this is f/11, 400 ISO, 1/800. That may not have been the optimum combination for IQ but in terms of the exposure value that is exactly equivalent to a Sunny 16 exposure. As above, this has had no edits....
| HTTP response: 404 | MIME changed to 'image/png' | Byte size: ZERO |
So, within the space of a couple of hours my "correct" exposure value has only altered by 1/3 stop under the same/similar lighting conditions. While it is undoubtedly true that you should learn more about metering, metering modes, exposure setting and exposure compensation, if you want an easy route to more consistent exposure in bright sunny conditions then try setting a manual exposure that matches a "Sunny 16" exposure or just a little bit less for beach scenes. You may still have to deal with the issue of shadows and providing fill light for those, but that's a topic for another day.
