All Figures

$\begin{figure} \par\includegraphics[width=8.8cm]{fig1.eps} \end{figure}$ Figure 1: A DSS red map of the covered region in the field of Berkeley 73. North is up, East to the left.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm]{fig2.eps} \end{figure}$ Figure 2: A DSS red map of the covered region in the field of Berkeley 75. North is up, East to the left.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm]{fig3.eps} \end{figure}$ Figure 3: A DSS red map of the covered region in the field of Berkeley 25. North is up, East to the left.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{fig4.eps} \end{figure}$ Figure 4: Star counts in the area of the three open clusters under study as a function of radius. The dashed lines represent the level of the control field counts estimated from the accompanying control field.
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In the text

$\begin{figure} \par\includegraphics[width=14cm]{fig5.eps} \end{figure}$ Figure 5: V vs. (B-V) ( left panels) and V vs. (V-I) ( middle panels) CMDs of Berkeley 73 ( lower panels), Berkeley 75 ( middle panels) and Berkeley 25 ( upper panels) and corresponding control fields ( right panels). We include all stars in each field.
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In the text

$\begin{figure} \par\includegraphics[width=14cm]{fig6.eps} \end{figure}$ Figure 6: B-V vs. V-I diagram for the four clusters. The solid line is the normal reddening law, whereas dashed and dotted lines are the intrinsic colors for luminosity class III and V, respectively. See text for details.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{fig7.eps} \end{figure}$ Figure 7: Isochrone solution for Berkeley 73. The solid lines are isochrones for the age of 1500 million year and metallicity Z=0.008. The apparent distance modulus is (m-M)=15.3, and the reddening E(B-V)=0.12 and E(V-I)=0.18. Only stars within the derived radius are shown. The dashed line in the left panel is a Z=0.019 isochrone for the age of 2 Gyr. See text for more details.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{fig8.eps} \end{figure}$ Figure 8: Isochrone solution for Berkeley 75. The isochrones (solid lines) are for the age of 3 Gyr and metallicity Z=0.004.The apparent distance modulus is (m-M)=15.2, and the reddening E(B-V)=0.08 and E(V-I)=0.13. Only stars within the derived radius are shown. The dashed line is a 3.5 Gyr, Z=0.008 isochrone. See text for more details.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{fig9.eps} \end{figure}$ Figure 9: Isochrone solution for Berkeley 25. The isochrones (solid lines) are for the age of 4 Gyr and metallicity Z=0.008. The apparent distance modulus is (m-M)=15.8 and the reddening E(B-V)=0.17 and E(V-I)=0.24. Only stars within the derived radius are shown. The dashed line is a 3.5 Gyr, Z=0.004 isochrone. See text for more details.
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In the text

$\begin{figure} \par\includegraphics[width=6.5cm]{fig10.eps} \end{figure}$ Figure 10: Age histogram of old open clusters. See text for details
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm]{fig1.eps} \end{figure}$	Figure 1: A DSS red map of the covered region in the field of Berkeley 73. North is up, East to the left.
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$\begin{figure} \par\includegraphics[width=8.8cm]{fig2.eps} \end{figure}$	Figure 2: A DSS red map of the covered region in the field of Berkeley 75. North is up, East to the left.
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$\begin{figure} \par\includegraphics[width=8.8cm]{fig3.eps} \end{figure}$	Figure 3: A DSS red map of the covered region in the field of Berkeley 25. North is up, East to the left.
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$\begin{figure} \par\includegraphics[width=8cm]{fig4.eps} \end{figure}$	Figure 4: Star counts in the area of the three open clusters under study as a function of radius. The dashed lines represent the level of the control field counts estimated from the accompanying control field.
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$\begin{figure} \par\includegraphics[width=14cm]{fig5.eps} \end{figure}$	Figure 5: V vs. (B-V) ( left panels) and V vs. (V-I) ( middle panels) CMDs of Berkeley 73 ( lower panels), Berkeley 75 ( middle panels) and Berkeley 25 ( upper panels) and corresponding control fields ( right panels). We include all stars in each field.
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$\begin{figure} \par\includegraphics[width=14cm]{fig6.eps} \end{figure}$	Figure 6: B-V vs. V-I diagram for the four clusters. The solid line is the normal reddening law, whereas dashed and dotted lines are the intrinsic colors for luminosity class III and V, respectively. See text for details.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{fig7.eps} \end{figure}$	Figure 7: Isochrone solution for Berkeley 73. The solid lines are isochrones for the age of 1500 million year and metallicity Z=0.008. The apparent distance modulus is (m-M)=15.3, and the reddening E(B-V)=0.12 and E(V-I)=0.18. Only stars within the derived radius are shown. The dashed line in the left panel is a Z=0.019 isochrone for the age of 2 Gyr. See text for more details.
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$\begin{figure} \par\includegraphics[width=8cm]{fig8.eps} \end{figure}$	Figure 8: Isochrone solution for Berkeley 75. The isochrones (solid lines) are for the age of 3 Gyr and metallicity Z=0.004.The apparent distance modulus is (m-M)=15.2, and the reddening E(B-V)=0.08 and E(V-I)=0.13. Only stars within the derived radius are shown. The dashed line is a 3.5 Gyr, Z=0.008 isochrone. See text for more details.
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$\begin{figure} \par\includegraphics[width=8cm]{fig9.eps} \end{figure}$	Figure 9: Isochrone solution for Berkeley 25. The isochrones (solid lines) are for the age of 4 Gyr and metallicity Z=0.008. The apparent distance modulus is (m-M)=15.8 and the reddening E(B-V)=0.17 and E(V-I)=0.24. Only stars within the derived radius are shown. The dashed line is a 3.5 Gyr, Z=0.004 isochrone. See text for more details.
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$\begin{figure} \par\includegraphics[width=6.5cm]{fig10.eps} \end{figure}$	Figure 10: Age histogram of old open clusters. See text for details
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