Ok, so now my stupid factor is going to jump right out at ya but I want to know. If I have a 2.8 lens and a 5.6 lens both mounted on tripods shooting a senic at f16, does the 2.8 lens automatically gather more light than the 5.6 lens? I know everyone drools over the fastest lens but if shot at a greater depth of field is there any difference?
Well if I understand the question, both lenses are at f16, then they gather the light the same since the aperture is the same size. Wide open, the 2.8 would gather more light than the 5.6.
No, at f/16 they both will gather the same amount of light.
f/2.8 would be better than a f/5.6 lens when both are being shot wide open and in lowlight or if you want shallower depth of feild/better Bokeh. Faster glass allows you to shoot with a faster shutterspeed/handheld lowlight than a slower lens. The disadvantage is you have a larger/heavyer/more expensive lens compared to the f/5.6 lens.
Suprisingly (and counter-intutitively), you're both technically incorrect (although as it turns out you're probably right in most cases).
Although photographers have gotten used to the idea that a certain aperture value equates to a certain amount of light transmission, that simply isn't the case. The f-stop is a measure of the ratio of the aperture diameter to the focal length -- not the measure of light transmission.
In fact, I can illustrate this quite clearly. Imagine I have two 50/1.8 lenses, but one lens is made from the glass used to make neutral density filters (or, if you're less photo-inclined, sunglasses). When they are both set to f/1.8, clearly the lens made of clear glass will transmit MORE light despite the fact they share the same f-stop.
Luckily for us, most lenses are somewhat similar in their transmission values, and so the t-stops for most lenses (transmission-stops) correspond to their f-stops so that f/16 on one lens produces a somewhat similar exposure to f/16 on another lens. The key term is "somewhat" -- for example, some people have noted that the 24-105 IS lens is "slower" than their other lenses at f/4.
This is why I suggest that the other posters are "probably" right -- two modern lenses at f/16 probably have similar (if not identical) t-stops.
EOS20 wrote:
No, at f/16 they both will gather the same amount of light.
f/2.8 would be better than a f/5.6 lens when both are being shot wide open and in lowlight or if you want shallower depth of feild/better Bokeh. Faster glass allows you to shoot with a faster shutterspeed/handheld lowlight than a slower lens. The disadvantage is you have a larger/heavyer/more expensive lens compared to the f/5.6 lens.
That's not necessarily true the wider aperture lens suffers from diffraction at a wider threshhold than the narrower aperture lens. It may not occur at f/16, but you could be less than a stop away.
Remford wrote:
the wider aperture lens suffers from diffraction at a wider threshhold than the narrower aperture lens. It may not occur at f/16, but you could be less than a stop away.
