WFPC2 allows only certain quantized exposure times. This quantization is disregarded during computations herein.
Allowed exposure times (seconds):
0.11 0.12 0.14 0.16 0.18 0.20 0.23 0.26 0.30 0.35 0.4 0.5 0.6 0.7 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.3 2.6 3.0 3.5 4 5 6 7 8 10 12 14 16 18 20 23 26 30 35 40 50 60 70 80 100 120 140 160 180 200 230 260 300 350 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700 3800 3900 4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000 5100 5200 5300 5400 5500 5600 5800 6000 6200 6400 6600 6800 7000 7500 8000 8500 9000 10000 15000 20000 25000 30000 40000 50000 75000 100000