Because Constable sensed he was not a natural portraitist he remained an unadventurous one. As portraits increase in size they also increase in difficulty: the majority of his portraits were painted in the smaller established formats, three-quarters (head and shoulders) or Kit-Cat (head and shoulders with hands). These unshowy sizes suited his sitters too. As the magpie of gossip Joseph Farington noted in 1804, Constable charged two and three guineas and "this low price affords the farmers &c to indulge their wishes and to have their Children and relatives painted".

This is nevertheless a fascinating exhibition because it gives an opportunity to see a significant painter confronting his limitations. And Constable could, at times, surpass himself - especially when the sitter was someone close to him. The exhibition includes several pictures of his wife and children that are marked by a rare sweetness and informality. The small head of his wife, painted in 1816, shortly before their marriage, shows something of the depth of the bond they had formed during their troubled courtship. Painted with the flickering bush strokes he usually reserved for nature, Maria exudes serenity and a moist-eyed softness. Constable took the picture with him when he went away and placed it next to his bed so that it was the last thing he saw at night and the first thing he saw in the morning. With this portrait he forgot to be constrained and lived up to his dictum that "painting is but another word for feeling".

At the British Museum, the third of its exemplary exhibitions exploring the patronage of great world leaders has just opened. After the First Emperor and Hadrian it is now the turn of Shah ‘Abbas, ruler of Iran from 1587 to 1629. This series has so far proved a minor revelation, showing that there is an appetite for old-fashioned didacticism when it is proffered by scholarly and imaginative curating.