We present new estimates of the observed rates of SNe determined with the control time method applied to the files of observations of two long term , photographic SN searches carried out at the Asiago and Sternberg Observatories .
Our calculations are applied to a galaxy sample extracted from RC3 , in which 65 SNe have been discovered .
This relatively large number of SNe has been redistributed in the different morphological classes of host galaxies giving the respective SN rates .

The magnitude of two biases , the overexposure of the central part of galaxies and the inclination of the spiral parent galaxies , have been estimated .
We show that due to overexposure a increasing fraction of SNe is lost in galaxies of increasing distances .
Also , a reduced number of SNe is discovered in inclined galaxies ( i > 30 \degr ) : SNII and Ib are more affected than Ia , as well as SNe in Sbc-Sd galaxies with respect to other spirals .

We strengthen previous findings that the SN rates is proportional to the galaxy blue luminosity for all SN and Hubble types .

Other sources of errors , besides those due to the statistics of the events , have been investigated .
In particular those related to the adopted SN parameters ( Cappellaro et al .
( [ 1992 ] ) ) and correction factor for overexposure and inclination .
Moreover , we show that the frequencies of SNe per unit luminosity vary if different sources for the parameters of the sample galaxies are adopted , thus hampering the comparison of SN rates based on different galaxy samples .

The overall rates per unit blue luminosity are similar to the previous determinations but significant differences show up for individual types .
In particular , the rate in ellipticals , 0.11 SNu ( H = 75 km s ^ { -1 } Mpc ^ { -1 } ) , is significantly lower than previously reported and better agrees with the predictions of galaxy evolutionary models .
Contrary to recent claims , in late spirals the rates of SNIa ( 0.39 SNu ) and Ib ( 0.27 SNu ) are similar .
The most frequent SNe in spiral galaxies are SNII ( 1.48 SNu ) .
Even the possible occurrence of faint SNe similar to SN 1987A ( < 0.5 SNu in late spirals ) does not significantly alter the total rate of SNII .

In the Galaxy , the expected number of SNe is 1.7 \pm 0.9 per century .