Started Nov 16, 2013 | Discussions thread
Re: m43 instead of FF - nuts!

inasir1971 wrote:

Ontario Gone wrote:

Yea, the idea of a larger sensor is a tricky thing. This is bc sensor size is not the only factor in light gathering, lenses are the other half of the equation. This is where it gets hairy. The problem is, some people want to claim bigger sensors are always going to be better (in regards to noise, in this conversation). On a static scale, this is true, but price is ALWAYS a factor for 99% of us. Since larger apertures cost more, and since larger sensors require larger apertures to get that extra light, cost will always be tied in.

????? This is just completely wrong. The physical aperture size is given by focal length / f-number! For a given focal length and max aperture given by f-number the aperture size is identical irrespective of sensor size.

I'm not sure i possess the vocabulary to show exactly what i mean here, but i will try to do so through some general explanation. We know that F stop is the aperture divided into the FL. A 50mm @ F/2 means there is a 25mm bottleneck aperture (50mm / 25= 2). But it's not as simple as this, because we also know, if this 50mm lens was a FF lens, slapping it on an APSC camera is going to waste some light, which is the reason for the crop factor (the sensor only records the center portion, giving the appearance of zoom, exactly what a TC does). The opposite is true if you put a crop lens on a FF camera, you get vignetting, not a wide enough light path to cover the larger sensor.

This means that a FF 50mm F/2 lens lets more total light through than a crop 50mm F/2 lens. But how is this possible if we look at F stop and say that's the entire situation? F stop is there only to tell us the intensity of the light path, but it says nothing about the diameter of the light path. That is why a lens must be fitted by format. This is also why we can put a speed booster on a FF lens+APSC camera, and get a faster lens. The speed booster condenses the light path, adding in what was previously wasted. This ends up giving a smaller F stop, or larger effective aperture, and shorter FL. In this situation, did the physical aperture change? No, it's still the same lens, we didn't use a ray gun to stretch it, but the F stop and FL changed bc we changed the angle of the light path.

Iv'e never seen a technical explanation, and it's hard to put to words in a chat room, but the above is true. Larger sensors require a larger light path, which does not necessarily mean a more intense light. It literally takes more light to expose a larger sensor, which is why they are "less efficient". Only when you increase the physical aperture and offer the same F stop does a larger sensor actually end up with an advantage, and larger physical apertures cost more. In theory (i have no idea who has tried it), one could take a FF camera, throw a crop sensor lens on it + a tc, and have no vignetting. It is thinning the light out to a wider path, lowering the effective aperture, lowering the intensity of the light path, and giving a slower SS.

I close with the following, screen captured from BobAtkins.com . This shows how the wide angle light, in red, is only captured by a larger FF sensor as it is able to catch a wider angle light path. This light is being "wasted" on a crop sensor, yet for either sensor size, the F stop is considered the same if we are to go by the F stop equation. If this were a FF 50mm @ F/2, it would be F/2 on either sensor size. An apsc 50mm F/2 would give the exact same SS on that crop sensor, but would not allow exactly the same amount of total light in the front element. Larger sensors can catch more light, but require physically bigger apertures to do so.

EDIT: lets be clear, i am aware the FF sensor is actually capturing more light, smaller sensors simply use more gain innately, which is why the have more noise. This however doesn't change the fact that larger glass is a must with larger sensors, and that means it costs more as well.

Ontario Gone's gear list:Ontario Gone's gear list
Nikon D7000 Canon EOS 70D Nikon AF-S DX Nikkor 35mm F1.8G Nikon AF-S Nikkor 50mm f/1.8G Canon EF 40mm f/2.8 STM
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