Boil just the raspberries and a quarter cup of water to a nice mush. Cool enough to handle. Run the mush through a food processor or blender in batches. Return to pan and bring to a boil.
Filter the hot juice through a clean hot water wetted muslin cloth to remove seeds and most of the pulp. Using heavy enough muslin to withstand the forces, you can twist the muslin into a tightened bag to force the juices, but this allows some pulp to filter through.
Return to pan, add 1/4 cup of the sugar and return to boiling, reducing volume to half its original. This intensifies the flavor. Add the lemon juice and half the remaining sugar.
While boiling slowly add enough of the remaining sugar to just thicken to the point where a heavy coating appears on a metal spoon when dipped and cooled. Don't add to much sugar or it will gel. Boil covered, about 5 minutes longer, cool and store in a glass bottle.
Refrigerated, it should pour from the bottle very slowly. Very little is required on foods, for the flavor is intense.