I have a 150 Symmar- S lens f/5.6. I know its a good lens but there seems to be a problem with the f/stops. I measured the diaphram hole after removing the rear element and checked the aperture at the different f/stops. Here is what I found :
f diameter(mm) new f ?
5.6 20.7 7.25 8 15 10 11 10 15 16 7 21.4 22 5.1 29.4 32 3.75 40 45 2.75 54
min hole 1.5 100
rear element stop 21.5 7
The lens shows almost a stop too slow for its setting. The max aperture can also only be f/7 since the rear element lens opening is 21.5 mm. What f/numbers are valid for this lens ? I also have a Componon 150 5.6 that shows the same apertur e sizes. Does the lens design compensate for the smaller holes ? Doesn't f/ratio = F.L./diameter always without exception ? Why does't this lens follow this gol den rule ?
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