a) ISAAC mosaicked image of SNR G21.5-0.9 in the [Fe II] 1.64 μm narrow-band filter. The full field of view is presented to show also the North Spur region. b) Same field of view as in panel a, but imaged in the 1.71 μm narrow-band filter. Faint diffuse emission at the NE and SW of the PWN is visible in 1.64 μm filter, and not in 1.71 μm. c) The [Fe II] 1.64 μm image after subtraction of the image in the 1.71 μm narrow-band filter. Some stellar residua are still visible; the net flux in these residua is typically around 9% (rms) of the corresponding stellar flux. For all panels: the star depicts the position of PSR J1833-1034; contours represent the extent of the X-ray PWN seen by Chandra ACIS (Slane et al. 2000). All images are presented with the same intensity scale. For presentation purposes, images were smoothed with a 2-dimensional Gaussian with σ = 0.28′′. The images shown include the data from the first night of observation (08.07.2002) only, in order to yield more uniform coverage of the PWN and North Spur regions.