File :-(, x, )
Anonymous
sup /p/

I have a few questions on the effect of aperture on exposure.

Does the diameter of a lens affect the exposure? If I shoot with the exact same focal length, aperture, shutter speed and ISO on a P&S and on a DSLR, will the photo from the DSLR be brighter because of the physically larger lens?

A 200mm lens at F/4 will have a physically larger aperture than a 50mm lens at F/4. Yet, both will produce similarly exposed photos, right? But does anyone have a link to a good explanation to what happens to the extra light in 200mm lens?

pic unrelated
EXIF data available. Clickhereto show/hide.
Camera-Specific Properties:Equipment MakeSONYCamera ModelDSC-W80Camera SoftwareAdobe Photoshop CS2 WindowsMaximum Lens Aperturef/2.8Image-Specific Properties:Image OrientationTop, Left-HandHorizontal Resolution72 dpiVertical Resolution72 dpiImage Created2008:05:18 20:53:32Exposure Time1/40 secF-Numberf/2.8Exposure ProgramNormal ProgramISO Speed Rating320Exposure Bias0 EVMetering ModePatternLight SourceUnknownFlashNo Flash, CompulsoryFocal Length5.80 mmColor Space InformationsRGBImage Width800Image Height600RenderingNormalExposure ModeAutoWhite BalanceAutoScene Capture TypeStandardContrastNormalSaturationNormalSharpnessNormal
>> Butterfly !xlgRMYva6s
http://upload.wikimedia.org/math/a/d/c/adcd8400b9cff8f5ae4ff1cac2074b07.png

http://en.wikipedia.org/wiki/Aperture
>> Anonymous
Yeah thanks, I've read guides, including the wikipedia page. Unless I misunderstood it, it says a 50mm lens and a 200mm lens will have a different area. Hence, my question. If the 200mm lens has a larger area, but the exposure is the same, what happens to the extra light the 200mm lens gathers?

And it does not seem to say anything about the physical size (diameter) of the lens (my first question).

Basically, is the amount of exposure indicated by an F number always the same, regardless of size, format, whatever? If yes, why does the diameter not matter? Or is there one F number for DSLRs, another for compacts, and yet another for miniature spy cameras, etc.
>> Anonymous
>>184109
>what happens to the extra light the 200mm lens gathers?
A 200/4 lens gathers the same amount of light as the 50/4 lens because the larger physical aperture size is cancelled out by the narrower spatial angle from which the light is collected.

>Basically, is the amount of exposure indicated by an F number always the same, regardless of size, format, whatever?

Yes. F-number determines the illuminance of the target surface (in lumens per unit of area), not the total amount of light gathered by the lens. Thus, a f/4 lens in a compact camera has to gather much less light than a f/4 lens on a DSLR because the latter has to cover a significantly larger sensor at the same illuminance.
>> Anonymous
>>184115
Thank you. To clarify, the sensor size is taken into account when giving F numbers? So if I replaced a DSLR sensor with a smaller one, and then somehow re-focused the light from a lens to cover the smaller area (assuming no loss of light in the process), the lens would, effectively, be faster? Would this change depth of field as well, or does the magical refocusing of light make the question meaningless?