2. Observations

In 1994-1995, BVRI photometric monitoring and fast photometry at I band for OJ 287 were carried out with the CCD attached to the focal reducer of the 1-m RCC telescope at the Yunnan Observatory, China. The CCD (Tek 512 mc) has pixels of . The field of view is . The characteristics of the filter are the same as that described in Schild (1983). The comparison star sequence is taken from Smith et al. (1985). The journal of observations is given in Table 1. The integration time and individual measurement errors in the I magnitude for the object and comparison stars 4, 10 and 11 as well as for a fainter star 5 (Visvanathan & Elliot 1973) are tabulated in Table 2. The averages of N/S ratio of flux for the object and stars 4 and 10 in each night are respectively listed in lines 2, 3 and 4 in Table 4.

**Table 1:** Fast photometry mode: journal of observations at I band
Date	Duration of	Number of	Average sampling
	Observations(hr.)	observations	interval (min.)
4/11/94	0.60	8	4.50
11/7/94	0.92	14	3.93
11/8/94	1.01	18	3.35
2/8/95	3.27	30	6.53
2/22/95	2.74	30	5.50
2/23/95	2.65	38	4.17

**Table 2:** Integrated time and individual measurement error on the I magnitudes of OJ 287 and comparison stars
Date	integrated	Error of individual measurement (mag)
	time(sec.)	OJ 287	4	10	11	5
4/11/94	150	0.011-0.013	0.005	0.007	0.008-0.010	0.014-0.016
11/7/94	100	0.006-0.007	0.006-0.007	0.008-0.011	0.010-0.012	0.017-0.021
11/8/94	100	0.006-0.007	0.006-0.007	0.009-0.010	0.010-0.011	0.017-0.019
2/8/95	200	0.008-0.010	0.004-0.005	0.006-0.007	0.007-0.008	0.010-0.011
2/22/95	200	0.007-0.010	0.004-0.005	0.005-0.007	0.006-0.008	0.011-0.012
2/23/95	150	0.011-0.012	0.005	0.007-0.008	0.008-0.009	0.013-0.015

Up: Microvariability of the