Three lines in the atomic spectrum of tin, $\lambda 3262$ angstrom, $\lambda 3283$ angstrom and $\lambda 6454$ angstrom have been studied in emission under high resolution with the use of light sources containing enriched isotopic samples. Results are reported for isotope shifts in these lines for the abundant stable isotopes $(A\geq 116)$. Pressure-scanned Fabry-Perot etalons provided the necessary resolution; the spectrograms for $\lambda 6454$ angstrom were recorded and analysed by digital techniques, and for this line hyperfine structure constants required in the interpretation of the data were also evaluated. The results for the three lines are not in good agreement with earlier work, but are shown to be self-consistent by means of a King plot. Their interpretation in terms of the nuclear charge distribution is considered in the following paper.