Snowdonia National Park

Light

Especially in late spring and summer the sun rises quite fast, so to photograph in “good light” you will need to get up very early and photograph until late in the evening. You can expect long days, starting at 4am and lasting until 23pm. During the day, when light is too harsh to photograph, you can use that time to catch some sleep or to explore the area and prepare what to photograph next.  On overcast days you should be able to take pictures the whole day.
In winter the sun stays low enough, giving you soft light and the opportunity to photograph the whole day.  That time of year, the days start and end at a reasonable hour, giving you plenty of time to get a decent breakfast or evening dinner afterwards.

Good to Know

Since you will be focusing mainly of landscape photography make sure to bring a wide range of lenses including a wide-angle lens (e.g. 17mm), a mid range lens (e.g. 24-70mm), a short telephoto zoom (e.g. 70-200mm) and a telephoto (e.g. 300 or 400mm). Try to pack as light as possible; the walks up and down the mountains can be pretty exhausting.  A good set of graduated ND filters and a polarizer filter are indispensible.
Accommodation can be easily found since there are plenty of campsites and bed and breakfasts around. If you are camping make sure you are well prepared against changeable weather, as nights can become pretty cold in the mountains, even in high summer.
Finally, always bring decent outdoor clothing and walking boots and especially during the summer months, protection against midges might prove helpful.

More Information

There is no official website about the national park, but useful information can be found at: http://www.snowdonia-wales.net. A decent map of the area is necessary and can be found at: http://www.ordnancesurvey.co.uk. For Snowdonia National park you need to look for OS Landranger map 115.
For more information on the mountain walks I would suggest the following guide:  “Pocket Guide to Snowdonia's Best Mountain Walks” by Carl Rogers.