We study the optical variability of the peculiar Galactic source SS 433 using the observations made with the Russian Turkish 1.5-m telescope ( RTT150 ) .
A simple technique which allows to obtain high-quality photometric measurements with 0.3–1 s time resolution using ordinary CCD is described in detail .
Using the test observations of nonvariable stars , we show that the atmospheric turbulence introduces no significant distortions into the measured light curves .
Therefore , the data obtained in this way are well suited for studying the aperiodic variability of various objects .

The large amount of SS 433 optical light curve measurements obtained in this way allowed us to obtain the power spectra of its flux variability with a record sensitivity up to frequencies of \sim 0.5 Hz and to detect its break at frequency \approx 2.4 \times 10 ^ { -3 } Hz .
We suggest that this break in the power spectrum results from the smoothing of the optical flux variability due to a finite size of the emitting region .
Based on our measurement of the break frequency in the power spectrum , we estimated the size of the accretion-disk photosphere as 2 \times 10 ^ { 12 } cm .
We show that the amplitude of the variability in SS 433 decreases sharply during accretion-disk eclipses , but it does not disappear completely .
This suggests that the size of the variable optical emission source is comparable to that of the normal star whose size is therefore R _ { O } \approx 2 \times 10 ^ { 12 } cm \approx 30 R _ { \odot } .
The decrease in flux variability amplitude during eclipses suggests the presence of a nonvariable optical emission component with a magnitude m _ { R } \approx 13.2 .