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Table 1
Log of observations.
| Filter | Exp. time | Airmass | Seeing |
| (s z) | (arcsec) | ||
|
|
|||
| NGC 6121 | |||
| u_HIGH | 25 × 410 s | 1.004–1.104 |  – |
| b_HIGH | 25 × 200 s | 1.007–1.113 |  – |
| v_HIGH | 25 × 52 s | 1.118–1.251 |  – |
| I_BESS | 25 × 30 s | 1.036–1.150 |  – |
| NGC 6397 | |||
| u_HIGH | 25 × 410 s | 1.153–1.452 |  – |
| b_HIGH | 35 × 200 s | 1.144–1.599 |  – |
| v_HIGH | 50 × 52 s | 1.142–1.272 |  – |
| I_BESS | 25 × 30 s | 1.251–1.355 | – |
| NGC 6752 | |||
| u_HIGH | 25 × 410 s | 1.227–1.416 |  – |
| b_HIGH | 33 × 200 s | 1.227–1.850 |  – |
| v_HIGH | 25 × 52 s | 1.367–1.483 |  – |
| I_BESS | 25 × 30 s | 1.293–1.363 |  – |
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