Should Equivalence go the way of the Dodo?

Started Aug 20, 2022 | Discussions thread
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lokatz Veteran Member • Posts: 4,406
Should Equivalence go the way of the Dodo?

Being relatively new to MFT, though with 25+ years of APS-C and FF shooting experience, I have observed a repetitive pattern on this forum where as soon as someone compares an MFT body or lens to an FF or APS-C one and highlights advantages, someone else steps in to point out how MFT results are intrinsically inferior compared to larger sensors, especially full frame. So as to avoid offense, this is often dressed up as a reference to what is referred to as if it were a fundamental law of physics: “According to Equivalence, this f/4 lens is really only an f/8 lens in FF terms.”

For simplicity, let me refer to folks using this kind of argument as ‘Equivalencers’. The Holy Grail these folks are bowing to essentially goes like this:

  • Equivalence Thesis 1:
    The crop factor of MFT is 2x, so MFT lenses need half the focal length for the same image.
  • Equivalence Thesis 2:
    Depth of Field is wider on MFT vs FF, so MFT lenses need two stops more aperture for the same shallow DoF.
  • Equivalence Thesis 3:
    The MFT sensor size is only one-fourth of FF, so MFT bodies need to shoot at an ISO that is two stops lower, or a shutter speed that is two stops slower, to get the same level of image noise.

I know, I know: some people here are sick and tired of discussing ‘equivalence’. I cannot help the feeling that those are usually the ones who take it as an unshakable truth. That kind of dogma unfortunately tends to provoke the rebel in me. If you’re interested, please read on to find out why I am a heretic:

Thesis 1 needs no debate, as we all know it to be correct. It spells out the main advantage of MFT, namely that the resulting lens size and weight can be smaller.

Thesis 2 is technically correct. Equivalencers usually make it sound like this is a bad thing. However, whether it indeed is, whether it is boon or bust, depends very much on what you shoot. If that’s portraits, you might not like the wide DoF of MFT, as good portrait shots often rely on shallow Depth of Field. For landscapes or architecture shots, it is a boon: with wide-angle MFT lenses, it almost does not matter where you focus, since pretty much everything from near distance to infinity is sharp anyway. When shooting birds and other small wildlife, a wider DoF is usually, though not always, a good thing: at the required focal lengths, shooting full frame often results in such a shallow depth of the sharp zone that only part of the animal is reasonably sharp. With MFT, this is less of a problem. With a bird sitting in dense shrubs, you may sometimes want less DoF, but that’s an exception. I experienced few scenarios where I would have liked less DoF in my MFT bird shooting so far. Lastly, there are other areas of photography, such as street or artistic shooting, where not getting that ultra-shallow DoF MAY be a disadvantage, but this can go either way. Neither a pro nor a con for MFT in my book.

Thesis 3 is again technically correct. At least, the first part of the statement is. If it was also practically relevant, its primary consequence would be that you’d either have to use much slower shutter speeds with MFT so as to compensate, or use only the lowest ISO levels, which would practically mean not shooting at all in very dim light. A huge disadvantage for MFT, right? Well, not really. Fortunately, you do not need to lower your shutter speeds and you should not fear high ISOs, either. In my opinion, this whole argument bears far less practical relevance than most people seem to believe.

I suspect that many Equivalencers initially moved from film to digital using D1Xs, EOS 1Ds and similar bodies. With that generation of digital cameras, users learned quickly that they needed as much light as possible to keep image noise manageable. Wide apertures = “fast” lenses were paramount. This historic reference is why I am reminded of the Dodo, that long-extinct bird: needing fast glass to prevent noise from being an issue is a thing of the past.

For starters, sensor noise is substantially lower now than it used to be. A state-of-the-art MFT body has less noise at ISO 800 than any digital camera before 2010 had at ISO 200, so shooting at higher ISOs now isn’t much of an issue. You can take images with any newer MFT body that exceed the technical quality of almost anything available before 2010, so there is no hurdle whatsoever to keep you from producing photographic masterpieces.

“But,” I hear the Equivalencers say, “comparing MFT with outdated bodies does not make sense. You need to compare your MFT camera to a current FF one.” This is a dubious argument to start with (shouldn’t good enough be good enough?), but, fair enough, let’s investigate it. (Spoiler alert: even when taking this point seriously, I find that it does not hold much water.)

For one, noise is now pretty much a non-issue with MFT up to ISO 800 or so, so when staying below this level, it is a “don’t care” with any of these sensor formats. More importantly, in this day and age of post-processing software performing miracles, noise is not much of an issue anymore at even higher ISO levels. Sure, there is a limit to everything, including ISOs, but I’ll happily shoot birds with my OM-1 at ISO 12,800, 16,000, even 25,600, because I know from experience that state-of-the-art NR engines (DxO, Topaz DeNoise, ON1; soon to be joined by Luminar Neo?) all but eliminate image noise without making the image notably softer, as older NR engines did. The results are in no way inferior to what I used to get with my Nikon D500 or D850, or with my Canon R5. This eliminates the MFT noise disadvantage. If, after suitable post processing on both sides, you still think your FF pics have notably less noise that somebody else’s MFT ones, please realize that you are a) a pixel peeper, and b) nearing extinction: it is a safe bet to predict that further progress in NR engines will completely eliminate perceptible noise as an issue in just a few years. I argue that for all practical purposes, we are already there.

Bottom line: if you shoot MFT, be prepared to invest more time in post processing when shooting in low light, but don’t think you’re using an inferior system. An f/4 lens is an f/4 lens on every system, no matter what the sensor size, so your 300mm f/4 Olympus lens, for example, in the same light will produce a brighter image on your MFT body, or allow you to shoot at faster shutter speeds, than a Canon or Nikon 600mm f/5.6 will on their respective ones. This is true in spite of the Oly lens being much smaller, lighter and cheaper. What’s not to like?

So, should the Equivalence theory go the way of the Dodo? In my view, it is important to understand the principles behind it, but it would be a mistake to take any of them, or all of them collectively, as “the answer”. In photography, things are rarely THAT black&white.

And if an Equivalencer tells you that your f/4 lens is really an f/8 lens, as I again saw a “Veteran” stating on this forum just a few days ago, flip them the Dodo.

 lokatz's gear list:lokatz's gear list
Sony RX100 VII Canon EOS R5 OM-1 Panasonic Lumix G9 II Olympus Zuiko Digital 1.4x Teleconverter EC-14 +32 more
Canon EOS R5 Canon EOS-1Ds Nikon D500 Nikon D850
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