View Full Version : Symmar-S // Componon-S rear element focal length & aperture?

28-Sep-2010, 14:11
I was playing around with my 360mm Symmar-S MC and 240mm Componon-S and when removing the front element I found the resulting image very soft and pleasing - just like it is with convertible Symmars.
But I was wondering what focal length and aperture I was dealing with...
When I look at my 150mm Symmar Convertible the rear element has a focal length of 265mm/f12, so I guess it might result in a 636mm/f14 (something) for the 360mm and a 424mm/f12 for the 240mm.
Now I know the actual design of the lenses is different so the focal length may vary - but would those be good estimates? What about the aperture?

Mark Woods
28-Sep-2010, 15:02
Focal Length is determined by the distance of the center of the lens design to the film plane when the lens if focused at infinity. The F/stop is the fraction of the FL. For example, F/16. The iris opening is 1/16 of the FL. You should be able to figure out pretty accurately what FL your lens is and the F/stop.

28-Sep-2010, 16:02
Now that's interesting... the 360mm rear element has 500mm and an f-stop of 14, the front element about 660mm f13.5 and the 240mm rear element is actually about 300mm f10...the front element is a 550mm f18...does that sound about right?