The Difficulty in Explaining Equivalence

Wow!!!! I have never been accused of being a DPReview moderator. That's a new one.

Even if I was a moderator it would be inappropriate to discuss other moderators' actions here.

Sorry, you seemed very well informed.

I am no more informed than what is publicly available on DPR Forums at

www.dpreview.com/faq#q14

and my own experience there.

I don’t doubt that is true but totally irrelevant to what DPR Admin are able to see.

You seem to have reversed your decision to leave this forum. Time to change your name again?

We like this name.

What?! TC misrepresented Equivalence (again) and locked a thread when this misrepresentation was challenged?! Say it isn't so! 😁😁😁

Anyway, let's keep this simple for the PM exchange. People rarely argue the validity of perspective, framing, DOF, and exposure time with regards to Equivalence -- it's always the noise end, so let's just concentrate on that point. To that end, the main disconnect for the anti-Equivalence crowd is two-fold:

1) What is the difference between and relevance of Exposure vs Total Light.
2) What the sources of noise in a photo are.

The problem is, no matter how well explained, "they" simply refuse to change their preconceptions. That is, exposure is the be-all and end-all and noise is entirely a result of the sensor. You can create an extended syllogism (a=b, b=c, c=d, d=e, e=f) and they may or may not accept each link in the chain, but at the end, when you conclude that this means a=f, they go right back to square one.

So, let's create the chain. For most all photography, there are two primary sources of noise: the noise that is inherent in the light itself (a law of physics thing, not a technology thing), called "photon [shot] noise", and the additional electronic noise, often called "read noise", added by the sensor and supporting hardware. The former is typically the dominant of the two sources, and the only role the sensor plays in this source of noise is what proportion of light projected on the sensor is recorded (QE -- "Quantum Efficiency") which is pretty much the same for sensors of the same generation and has been relatively unchanged in the past decade.

The photon noise for a particular portion of the photo is entirely a function of the total amount of light that made up that portion of the photo. For example, if 4x as much light makes up a portion of the photo, that portion will be half as noisy (not including the electronic noise).

The electronic noise matters more in the portions of the photo made with very little light (e.g. the deep shadows at base ISO and progressively more of the photo as we use higher ISO settings to "compensate" for the lesser light). This has a huge effect on the DR of a photo, and the differences in electronic noise between sensors varies considerably more than the differences in QE, thus the greater variability of DR, which we will see when pushing shadows heavily and progressively more and more of the photo as we use higher ISO settings to "compensate" for lower and lower light (typically "significant" past, say, light levels where you'd be using ISO 6400 and higher).

The exposure is a function of the scene luminance, f-number, and exposure time whereas the total light is a function of the scene luminance, aperture diameter (yes, measured in millimeters), and exposure time. It is important to realize that the aperture diameter is also intimately involved with DOF, so, for a given scene and exposure time, DOF and noise are directly related. For example, for a given scene, perspective, framing, and exposure time, f/2.8 on mFT will have twice the DOF and be twice as noisy as f/2.8 on FF because the aperture diameter for FF is 2x larger, whereas the DOF and noisiness will be the same for f/2.8 on mFT and f/5.6 on FF, as the aperture diameters are the same.

If these points are not clearly understood, then further [productive] discussion is not possible, so that must be tackled first in any honest discussion.

That's something you as admins should, if you haven't already done so, discuss with your legal advisers.

the understanding of most photographers about equivalence is DoF, the problem is no one really wants to discuss equivalence practically. i posted 3 images of the same subject with 3 different sized sensors with the same settings and the dof looks the same depth, just with broader transitions. the major difference is background blur and field compression.

If the transition, background blur and field compression are different then the dof is not the same according to the commonly accepted definition of dof.

Perhaps you are using a different definition of dof?

but they are discussing more dof to fit more faces in focus when changing sensor size. must admit so does all the calculators but in practice i cant see any difference in what is critically sharp.

If you're talking about the photos of the little plastic bottle, the DOF is not the same.

Maybe you're talking about some other photos.

If there's something you believe about equivalence that others here don't believe, state exactly what that is.

If there's something you don't believe about equivalence that others here believe, state exactly what that is.

Either way, I'm sure I can stage a practical demonstration that shows the reality.