Gratings appear of higher spatial frequency when they are viewed peripherally rather than foveally. To test the hypothesis that this effect is an artefact of particular laboratory conditions, we manipulated the contrast, luminance and presentation duration, manipulations which have also been shown to increase the apparent spatial frequency of foveally presented gratings. It has been argued that such shifts reflect an attempt to increase sensitivity by changing the receptive field properties of spatially tuned visual channels, while keeping their size labels constant. If so, and peripheral channels are not otherwise mislabelled, it should be possible to find conditions under which the apparent spatial frequency of peripherally viewed gratings matches that of foveal gratings of the same spatial frequency. In this study, manipulations of contrast, luminance, and duration had no effect on the size of the perceived spatial frequency shift in peripheral vision. Thus the putative inappropriate size labelling of peripheral visual channels is constant over a wide range of stimulus values. We speculate that this apparent constant error may result from a mechanism which normally compensates for another factor such as blur, which may otherwise lead to an overestimation of size.