Bokeh

[Inkanyezi]

oh and one more little tidbit for thought....

Bokeh is determined by your aperture aka f-stop. well. i could take that 35mm and shoot at f/2. then take the 135mm and shoot at f/2. i could shoot a subject, and frame them the same way in both shots (the body fills the frame from head-to-toe), BUT the pictures would look very different. the bokek/background blur would be very different. why? i'm shooting at the same aperture, right? why the difference in the appearance of the image? why isn't all bokeh created equal?

Anyone?

No, you are not shooting at the same aperture. The aperture of your 135 mm lens at f/2 is 67.5 mm diameter, while it is only 17.5 mm with the 35 mm lens. As distance increases from your subject, the apparent size of the aperture of the wide angle lens, as seen from the subject or background, is shrinking much faster than the one of the tele lens, and therefore detail in the background will be less blurred. As the lens also covers a wider angle, there will mostly also be more detail to clutter the background. Bokeh, just as depth of field bears a relation to the image size on the sensor and the f-number, but it can also be expressed as the angle of the entrance pupil of the lens as seen from the subject. This angle rapidly decreases with distance for a wide angle lens, much more than for a tele lens, where subject distance is larger from start when it is the same size on the sensor.