changing vertical scale of log plot

edit

Could you please tell me how to change vertical scale in logarithmic plot?

In the following code I didn't set size of the vertical scale. So the result looks bad. How can I change the interval?

var('q1, q2, q3, q4, q5, o1, o2, o3, o4, o5, Lo1, Lo2, Lo3, Lo4, Lo5')

q1=1/20^2*exp(-20/L_s);
q2=2.4/20^2*exp(-20/L_s);
q3=4/20^2*exp(-20/L_s);
q4=5/20^2*exp(-20/L_s);
q5=15/20^2*exp(-20/L_s);

o1=plot(q1, (x, 0, 90), ymin=0, ymax=0.03, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=True, legend_label='I=1 cd', frame=True, color='yellow', title='r(distance)=20m');
o2=plot(q2, (x, 0, 90), ymin=0, ymax=0.03, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=False, legend_label='I=2.4 cd', frame=True, color='red');
o3=plot(q3, (x, 0, 90), ymin=0, ymax=0.03, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=False, legend_label='I=4 cd', frame=True, color='blue'); 
o4=plot(q4, (x, 0, 90), ymin=0, ymax=0.03, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=False, legend_label='I=5 cd', frame=True, color='black'); 
o5=plot(q5, (x, 0, 90), ymin=0, ymax=0.03, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=False, legend_label='I=15 cd', frame=True, color='green'); 
o5.set_legend_options(loc=2);

show (o1 + o2 + o3 + o4 + o5)

Lo1=plot(q1, (x, 0, 90), scale='semilogy', ymin=0, ymax=0.1, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=True, legend_label='I=1 cd', frame=True, color='yellow', title='r(distance)=20m');
Lo2=plot(q2, (x, 0, 90), ymin=0, ymax=0.1, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=False, legend_label='I=2.4 cd', frame=True, color='red');
Lo3=plot(q3, (x, 0, 90), ymin=0, ymax=0.1, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=False, legend_label='I=4 cd', frame=True, color='blue'); 
Lo4=plot(q4, (x, 0, 90), ymin=0, ymax=0.1, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=False, legend_label='I=5 cd', frame=True, color='black'); 
Lo5=plot(q5, (x, 0, 90), ymin=0, ymax=0.1, axes_labels=['Scattering length [m]','Illuminace on camera sensor[lux]'],axes=False, legend_label='I=15 cd', frame=True, color='green'); 
Lo1.set_legend_options(loc=4);

show (Lo1 + Lo2 + Lo3 + Lo4 + Lo5)