# 1" sensor versus APS-C

Started Aug 15, 2013 | Discussions thread
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 Re: 1" sensor versus APS-C In reply to ultimitsu, Aug 22, 2013

ultimitsu wrote:

nigelht wrote:

Therefore we can conclude that Camera A at 54mm/2.8 received 9 times as much light as Camera B at 18mm/2.8.

Yes but that light has to cover 9 times the surface area in Camera A than in Camera B. You aren't just lighting up the center crop of the Camera A sensor anymore. There are 9 sensor squares to light up instead of 1 square.

Ooops. This is where your thought experiment falls over. Hard.

I am not sure why you think the thought experiment fall over, your reply pretty much is in complete agreement to what this experiement is trying to show you. You have been enlightened!

It need to be noted that no one said the 54mm/F2.8's light (on camera A) is 9 times more intense than 18mm/2.8 on camera B (which is what you seem to imply I have said, thus claiming there is a mistake). The intensity are the same (because they are both F/2.8), but there is 9 times more light passing through the 54mm, evenly distributed on the sensor of Camera A; i.e, per area, light is the same, but because Camera A has 9 times the sensor are, overall light is 9 times more.

Total light will reduce noise but doesn't do anything for you in terms of exposure of the final image.  Your sensor is calibrated to output Y given X input.  You've just provided 1/9th the input required to get the correct output.

There is no guarantee that your Camera A can generate the correct output at all with a 3 stop deficit.

If we reduce aperture diameter of the 54mm lens down to one third, we would get a f-ratio of 8.4 and diameter of 6.43mm. The amount of light that comes through the 54mm/8.4 is only 1/9 of the 54mm/2.8. The same amount as Camera B with 18mm/2.8.

Except that you need to spread that light across the much larger sensor area of Camera A making every square 1/9th as bright as the sensor on Camera B requiring 9 times the sensor sensitivity to generate the same output.

Exactly correct. Camera A's image would have to be ISO 900 if Camera B's was ISO 100. And they will look the same.

I am glad we got this all sorted, you are no longer stuck in that wrong mind set!

No.  This is wrong.

There can be no assumption that Camera A can do 3 stops better.

This works at ISO 100 but if I'm at ISO 3200 on the V1 the equivalent will be ISO 25,600+.  If I'm at ISO 6400 on the V2 the equivalent is ISO 51,200+.

Some cameras wont do 51,200.  Hey, look...like the D600 and D800.

Some cameras wont do over 25,600 leaving you a bit underexposed even compared to the V1.

With the Canon 1Ds Mk III you're topped out at ISO 6400.

The classic 5D MKII last sold in 2011 is only getting to 25,600.

And don't give me any hooey about nobody using 6400 on the V2.  I use 3200 all the time on the V1 and I'm stuck at 1/60 shooting people moving quickly so I'd gladly trade more noise at 6400 for less motion blur at 1/125.

1/60 means picking your shot very very carefully to get an "artful" blur or when the dancers are at rest and posing.

With a lens 3 stops slower the D600 is at 1/30 at max ISO.

the same diameter as the 18mm/2.8 lens for Camera B is 6.43mm, exactly the same as the diameter of the 54mm/8.4 lens.

A much slower 54mm/8.4 lens.

But we need to ask, what exactly is "slow"? Refer to Wikipedia - "A lens with a larger maximum aperture (that is, a smaller minimum f-number) is called a "fast lens" because it delivers more light intensity (illuminance) to the focal plane, achieving the same exposure with a faster shutter speed."

But as we have established, for the same shutter speed we end up with the same amount of light on sensor whicn in turn result in the same image, so for all practical purpose, the two lenses are of the same speed.

Wrong.  The lens is 3 stops slower, the D600 can only make up 2 stops so you're down a stop on shutter speed.  That's the D600.

No wait, let me guess, you're going to say "well, I'll just fix that in post" and shoot 1 stop underexposed and keep the shutter speed...see!  Same thing!  Except that I can underexpose and push the V2 in post as well.

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