Place the rosehips and the apples in a preserving pan. Add enough water to cover them and simmer gently for around 45 minutes until the fruit is soft and pulpy. Mash the fruit with the back of a spoon, then pour it into a jelly bag and leave undisturbed overnight, collecting the drips underneath in a measuring jug. Allowing your jelly to drip through slowly will ensure it sets clear.
Use 450g sugar to every 600ml juice (the general rule is 450g sugar to every 600ml juice will make roughly 750g jelly). Place the juice in a preserving pan, add the warmed sugar and stir over a low heat until all the sugar has dissolved, then turn up the heat and boil rapidly to reach setting point. Skim if necessary.
Pour the jelly into hot, sterilised jars and seal.