An apparatus (201, 301, 401, 501, 601, 701, 801, 901) comprising: first light guiding means comprising at least: first in-coupling diffractive means configured to in-couple one or more first input beams of light into the first light guiding means from a first light engine, first expanding means configured to expand the one or more first input beams of light from the first light engine to form one or more first expanded beams of light, first out-coupling diffractive means configured to out-couple the one or more first expanded beams of light from the first light guiding means; and second light guiding means comprising at least: second in-coupling diffractive means configured to in-couple one or more second input beams of light into the second light guiding means from a second light engine, second expanding means configured to expand the one or more second input beams of light from the second light engine to form one or more second expanded beams of light, second out-coupling diffractive means configured to out-couple the one or more second expanded beams of light from the second light guiding means; wherein the first light guiding means is configured to provide a first image, the second light guiding means is configured to provide a second image; wherein the apparatus is configured so that at least one of the first light guiding means and the second light guiding means can be moved between at least two different positions to change the relative position of the first light guiding means and the second light guiding means; wherein the apparatus is configured to maintain a combined exit pupil formed from outcoupled beams from the first light guiding means and the second light guiding means as the relative position of the first and second light guiding means is changed; wherein within at least a part of the combined exit pupil the image viewed is at least a part of the first image and at least a part of the second image. first light guiding means comprising at least: first in-coupling diffractive means configured to in-couple one or more first input beams of light into the first light guiding means from a first light engine, first expanding means configured to expand the one or more first input beams of light from the first light engine to form one or more first expanded beams of light, first out-coupling diffractive means configured to out-couple the one or more first expanded beams of light from the first light guiding means; and second light guiding means comprising at least: second in-coupling diffractive means configured to in-couple one or more second input beams of light into the second light guiding means from a second light engine, second expanding means configured to expand the one or more second input beams of light from the second light engine to form one or more second expanded beams of light, second out-coupling diffractive means configured to out-couple the one or more second expanded beams of light from the second light guiding means; wherein the first light guiding means is configured to provide a first image, the second light guiding means is configured to provide a second image; wherein the apparatus is configured so that at least one of the first light guiding means and the second light guiding means can be moved between at least two different positions to change the relative position of the first light guiding means and the second light guiding means; wherein the apparatus is configured to maintain a combined exit pupil formed from outcoupled beams from the first light guiding means and the second light guiding means as the relative position of the first and second light guiding means is changed; wherein within at least a part of the combined exit pupil the image viewed is at least a part of the first image and at least a part of the second image.