A reminder for some memebers as to what the F stop is all about.

Started Jan 26, 2014 | Discussions thread
Great Bustard Forum Pro • Posts: 43,017
Re: A simple Yes or No.

CollBaxter wrote:

Great Bustard wrote:

CollBaxter wrote:

Great Bustard wrote:

CollBaxter wrote:

Great Bustard wrote:

gsergei wrote:

Or why the light meter doesn't care.

Hello, again.

Let me repeat my point:

Given the same light source conditions and ISO setting the illumination, measured in lumens, received by any size of sensor is equal across all formats (no Ifs , no buts) , when cameras are set to the same A , S, ISO values. So, in practical terms this means, that the illumination received by my tiny c7070 at 125/5.6 and ISO 100 is exactly the same as on the so called FF sensor camera set to the same values. This will result in the same picture brightness/darkness , subject to DR and noise differences.

No one that I'm aware of claims that f/2 will not result in the same exposure regardless of format or focal length for a given scene luminance and shutter speed.

Please, do not feed me things like "amount of light", "sensor area", "light power" , "bigger lens opening" etc. and try to operate , using known physical terms and concepts.

If the difference between the amount of light per area that falls on the sensor (exposure), and the total amount of light the sensor records is difficult to understand, well...

Is the amount/intensity of light on a say a square cm at the center 4/3 , APS-C , APS-H , 1 inch , FF , 36X49 sensors at say f/2.8 not equal ?

A simple Yes or No.

Yes. Now, if you would return the favor:

For a given perspective, framing, and shutter speed will f/2 on 4/3 result in a photo with the same DOF as f/4 on FF as well as project the same total amount of light on the sensor, resulting in the same noise

A simple Yes or No.

Now, if I could trouble you for one more yes/no question:

We take a pic of the same scene from the same position at:

  • 50mm f/2 1/200 ISO 400 on 4/3
  • 100mm f/2 1/200 ISO 400 on FF
  • 100mm f/4 1/200 ISO 1600 on FF

Thanks for the answer . So a F/2.8 lens is a F/2.8 lens as far as light transmission , no mater what the sensor size is.

The same f-ratio results in the same light per area on the sensor for a given scene luminance, shutter speed, and transmissivity of the lens (i.e. the difference between the f-stop and t-stop).

But saying "a F/2.8 lens is a F/2.8 lens as far as light transmission" is misleading, 'cause an f/2.8 lens on 4/3 does *not* transmit the same amount of light to the sensor as an f/2.8 lens on FF.

As to the DOF we will all agree that DOF at the same F stop on different size senors are different. ( Hell I have been on this forum long enough to understand that) . Noise is another issue.

They are the same issue, actually. You see, for a given scene, perspective, framing, and shutter speed, it is the aperture (entrance pupil) diameter that determines the DOF and the total amount of light falling on the sensor, and thus, in combination with sensor efficiency, the noise.

Theatricality the first and the last would produce about the same noise and DOF and field of view . ( Assuming 2 stops advantage for the FF)

The "theoretically" is based on assuming the same sensor efficiency, which is usually fairly close for sensors of the same generation.

With the second having the least noise and shallowest DOF with the same field of view.

Specifically, half the noise and half the DOF.

It's all in the 2 Stops.

Yep. In practice, just as a sharper lens on 4/3 reduces the resolution advantage of FF, a more efficient sensor on 4/3 will reduce the noise advantage of FF. Likewise, a sharper lens on FF can extend the resolution advantage just as a more efficient sensor can extend the noise advantage.

I would say that, at higher ISOs, the advantage of modern FF over modern mFT is about 1.5 stops.

Now lets raise the sensor density to the same as the 4/3 camera. and what do we get. ?

The exact same thing, assuming, of course, that the higher density sensor is equally efficient.

Other than the second example having less DOF. A 64MP sensor would be about just as noisy on a FF never mind the corner and edge fall off , with the last example being the most noisy. The only advantage would be DOF control.

Consider the D600 vs the D800. The D800 has 50% more pixels than the D600. Is it more noisy?

You can't have your cake and eat it.  When you use words like assuning equal eficencey." if the sensors are equally efficient? " its up near the top somewhere.

Well, you can go to Sensorgen and see a partial list of sensor efficiencies.  You will note, for example, the the 5D2 and E5 sensors are almost exactly the same efficiency, as are the 6D and EM5 sensors.

If you want to compare a 10 year old sensor to a modern sensor we are just fish paste , fish pasting around here for the sake of fish pasting.

I'm not the one wanting to make such a comparison.  But, are you really going to argue that f/2.8 on an E1 is not f/2.8 on an EM1 because the EM1 sensor is more efficient?

Lets keep things equal with the theoretical and equal senors. Lets take your FF and chop it in 4 bits. Let not talk about a E-1 sensor as that's like comparing a model T Ford to the latest Ford models.


We talk light transmission you cloud it with area efficacy and the old DOF thing.

What do you mean by "light transmission"?  Do you mean the light per area falling on the sensor or the amount of light falling on the sensor?  You see, these are two very different things, and, in fact, at the core of the matter, and people are either ignorant of this distinction and what effect it has on the visual properties of the recorded photo, or they are intentionally deceptive in failing to acknowledge this simple concept.

A f/2 lens is a f/2 lens

And a 50mm lens is a 50mm lens.  But just as the effect of 50mm on 4/3 has the same effect as 100mm on FF, in terms of the visual properties of the photo, f/2 on 4/3 has the same effect as f/4 on FF, in terms of the visual properties of the photo.

You said ealier "You can't have your cake and eat it", and yet it is you, and all the other people who argue against Equivalence, that are trying to have their cake and eat it by completely sidestepping (either by ignorance or malice) the difference between the amount of light per area that falls on the sensor and the total amount of light that falls on the sensor, and what this has to do with the visual properties of the recorded photo.

And, FYI, while I take every care to say, for example, that 50mm f/2 on 4/3 is equivalent to (as opposed to "equal to") 100mm f/4 on FF, the fact of the matter is that a 50 / 2 lens with a 2x TC does equal a 100 / 4 lens, and if you put it in front of a FF sensor, it would take the same photos as the bare 50 / 2 lens in front of a 4/3 sensor.

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