Until you know for sure, it’s confusing to know who to believe. Is a 50mm f1.4 lens equivalent to a 75mm f1.8 on APS-C? Are Micro FourThirds sensors two stops noisier than full frame sensors? Can you get the ‘medium format look’ on APS-C by using a two stop faster lens?
If you want to know badly enough, may I recommend Joseph James’ excellent dive into the subject found here, which there’s no need to rehash here. The important takeaways are:
- etc
Queries like the above (frustratingly) tend to make certain assumptions that demand clear definition before meaningful answers can be given. Let’s consider some common assumptions and practical outcomes.
Assumption 1: Total Image Noise
Theory aside, an important assumption is your personal threshold of acceptability for noise. In practice – more than advances in hardware – refinements in post-production have raised the bar on this gradually over the last decade. Most sensors on the market in 2024 are only incrementally better than their 2014 counterparts, but in-camera and RAW processing algorithms are much smarter.
But let’s imagine we own a camera of each format, and define our primary goal as ‘acceptable’ noise levels in an 8000px wide image. A M43 or APS-C camera of 24MP will require noise-amplifying upsampling. A 40MP ‘full-frame’ camera is already at the target resolution, and a 100MP Fujfilm GFX will benefit from noise-shrinking downsampling. Let’s assume the native performance of each sensor sets the bar at an acceptable threshold (for instance) of ISO 3200 for the M43; ISO 4000 for the APS-C, ISO 6400 for the FF, and ISO 12,800 for the GFX. However, upsampling of the smaller image to 8000px will ‘cost’ us (for example) a stop of noise, and the downsampling of the larger image will gain us a stop. The M43 camera then needs to be limited to ISO 1600, and the APS-C to ISO 3200 – whereas we can safely shoot at ISO 25,600 on the GFX.
Let’s go further and make a second assumption – a common necessity when shooting in low light – that the shutter speed must be kept above 1/30. If a correct exposure can be gained in ambient light with the full frame at f2.0 / ISO 6400, the GFX ‘equivalent’ in terms of succesfully acquiring an image of 8000px at 1/30s is an aperture of f4.0. This is not at all to comment on the equivalence of depth of field, diffraction, or any other aspec of ‘the look’ – simply the temporal and practical mechanics of getting the shot. On APS-C, an aperture of f1.4 would be required. On M43, aperture of f1.0 would be required.
Practically, then, we might imagine the full-frame sensor as ‘one stop better at light-gathering’ than APS-C, two stops ahead of M43, and two stops behind the GFX format – even though formulating it in this way is incorrect. But if we set the bar at 8000px and demand a shutter speed of 1/30, it’s true enough.
What if we set the bar at a 1200px-wide destined for use on Instagram? In that case, it’s not necessary to make an adjustment for pixel-level noise: its effect on an image so hugely downsampled (from 24MP, 47MP or 100MP) is negligible. In fact, M43 is just as good as GFX, and all can safely be shot at ISO 25,600 or higher.
Of course noise isn’t the only issue: colour accuracy and dynamic range suffer at higher sensitivities – both will be visible at 1200px. Here we begin to make other assumptions on other quality criteria. Each new piece on the board increases the complexity of what we can fairly define as ‘equivalent’, and shifts the parameters of the conversation. For instance . . .
Assumption 2: Depth of Field
Operating on an entirely different assumption, let’s assume that the goal – independent of image size – is the apparent depth of field generated by a 50mm f2.0 lens. Crucially, this is not a fixed assumption: there’s no standardised benchmark of 50/2-ness.
Lenses of the same nominal specification vary widely with regard to the gradient of their focus transition and bokeh character – including the size and shape of defocused specular highlights in various sectors in the image circle. When placing a subject centrally, lenses with stronger aberrations in their outer image circle present as ‘faster’ than they are – inasmuch as they blur even in-focus subjects in Zones B and C. Field curvature – which is rarely linear – also weaves in and out of the theoretical focal plane to add its own signature – sometimes, for instance, bringing into sharper focus distant objects in the frame corners. Not all 50mm f2.0 lenses are equal, or even equivalent, with regard to apparent depth of field.
Having said that, in principle, a similar ‘look’ to 50/2.0 on full frame is achieved on APS-C with a 33.3mm f1.4, a 25mm f1.0 and a 75mm f2.8 on GFX.
Photographer’s seeking to maximise depth of field find a smaller sensor advantageous. Conversely, those seeking to maximise subject isolation find a larger sensor more useful.
But in practice it’s not that simple: smaller sensors generally have smaller pixels, which sets the diffraction limit lower. Photographers seeking maximum resolution find an aperture of f8 is well over the hill for M43, typically a bit past its best for full-frame, and broadly in the sweet spot for GFX. Requiring critical sharpness in the focal plane partially levels the (playing) field. Having said that, there is a ratio between the size of the front element and the exit pupil that factors into diffraction: small-diameter lenses are less impacted by diffraction-limiting than those with large-diameter front elements.
Another real-world factor is the availability of fast lenses in a given format. The smaller the image circle, the easier it is to deliver high transmission values within it. Larger format lenses typically have larger minimum f-values. The explanation for the absence of a commercially-available Canon L 24-70mm f1.4 zoom is more practical than technical: it would literally and metaphorically be a white elephant – huge and unsaleable.
Real-World Depth of Field Benchmarks
If we assume the desirability of greater subject isolation (‘maximum bokeh’), the following table awards a win in green for a given format and focal depth. We have not complicated the issue at this point by factoring in minimum focal distances, and only ranked the fastest commercially-available lens at each focal length in 2025. However, given the ease of adaptation, we have allowed all lenses with approppriately large image circles, regardless of the format for which they were intended. Please note this table only ranks the ability of lens on a given format to isolate the subject – ie, the thinnest focal plane combined with the longest hyperfocal minimum distance. As the Metabones website says: “When most people ask about depth-of-field, they are not interested in mathematics, but rather, they are after a certain kind of shallow depth-of-field “look”. ‘ The table also ignores the real (and irreconcilable) problem of FoV equivalence between formats of different ratios and simply adopts the real-world-perfectly-functional idea that the following is a ladder with rungs evenly separated by one stop. Focal lengths are here given as 35mm-equivalent.
| Micro 4/3 | APS-C | Full-Frame (35mm) | GFX/Hasselblad | |
| 14-19mm |
Native AF: -2½ stops Adapted AF: -1⅓ Stops |
Native AF: -1⅔ Stop Adapted AF: -⅔ Stop |
Native AF: BEST Sigma 14mm f1.4 |
Native AF: -1 Stop Native MF: -1 Stop Adapted AF: -1 Stop |
| 20-25mm |
Native AF: -4 Stops Native MF: -1 Stop Adapted AF: -⅔ Stop |
Native AF: –1 Stop Adapted AF: BEST |
Native AF: BEST Sigma 20mm f1.4 Sony 24mm f1.4 |
Native AF: -⅔ Stop Adapted AF: -1 stop |
| 26-30mm |
Adapted AF: -1⅔ Stop |
Native AF: 2 Stops Adapted AF: –1 Stop |
Native AF: -1 Stop Native MF: –⅔ Stop |
Native AF: –1⅔ Stops Adapted AF: BEST* |
| 32-40mm |
Native AF: –3 Stops Native MF: -2⅙ Stops Adapted AF: -2 Stops |
Native AF: -2 Stops Native MF: -1⅙ Stops Adapted AF: -1⅓ Stop |
Native AF: –1 Stop Native MF: –⅙ Stop |
Native AF: -⅚ Stop Adapted AF: BEST* |
| 45-65mm |
Native AF: -3 stops Native MF: -2⅙ Stops Adapted AF: -1 Stop |
Native AF: -2 Stops Native MF: -1⅙ Stops Adapted AF: -⅓ Stop |
Native AF: –1 Stop Adapted AF: -⅓ Stop Adapted MF: ⅙ Stop |
Native AF: -⅚ Stop Adapted AF: BEST* |
| 70-95mm |
Native AF: -2⅔ Stops |
Native AF: -1 Stop Adapted AF: -⅔ Stop |
Native AF: -⅔ Stop |
Native AF: –1 Stop Adapted AF: BEST |
| 100-175mm |
Native AF: -2⅔ Stops Native MF: Adapted AF: -⅓ Stop |
Native AF: -1 Stop Adapted AF: -1 Stop |
Native AF: -⅔ Stop |
Native AF: -3⅓ Stop Adapted AF: BEST Adapted AF: -1⅓ Stop |
| 180-250mm |
Native AF: -3⅓ Stops Adapted AF: -1⅓ Stop |
Native AF: –1 Stop Native AF: -1⅓ Stops Adapted AF: BEST |
Native AF: -⅓ Stop Adapted AF: BEST |
Native AF: -1⅓ Stops Adapted AF: -⅓ Stop |
| 300mm+ |
Native AF: -3 Stops Adapted AF: -1⅔ Stops |
Native AF: -1 Stop Adapted AF: -1 Stop |
Native AF: -1 Stop Canon 300mm f2.8 |
Native AF: -2 Stops Adapted AF: BEST |
Caveats & Takeaways:
- Between 20-25mm, Micro FourThirds has subject-isolating ability identical to medium format, and APS lenses are superior to both formats.
- Native medium format lenses only offer competitive subject-isolation between the focal lengths of 26-100mm and are heavily dependent on adapted lenses to match the capability of the 35mm format.
- Only when using one-off or unobtainium adapted lenses designed for 35mm can medium format match the subject-isolating capability of the 35mm format. These lenses are variously compromised in their outer image circle when stretched to the larger format, and therefore should not be considered full peers of native medium format glass. Every medium format ‘win’ is therefore questionable.
- The capability of 35mm-format lenses to achieve focus in a wide range of circumstances should not be underestimated. In most cases, state-of-the-art subject-isolation is achieved with native autofocus – greatly improving real-world performance.
- Game-changing optics like the Canon 50mm f1.0, Canon 200mm f1.8 and Sigma 105mm f1.4 – all currently discontinued in favour of less ambitious models – are more responsible for strong subject-isolation in this hierarchy than the scale of the imaging format. Ditto the Metabones Speedbooster – without which APS-C would make a poorer showing.
One more thing . . .
For a centrally-placed subject, strong field curvature and/or outer circle aberrations will convincingly impersonate a shallower depth of field if the foreground and background are spatially separated. The effect is entirely ruined by off-centre placement of an in-focus subject. But specifically in such composition a badly corrected f2.0 lens may give the impression of being one or more stops better at isolating a central figure than its aperture would suggest. Bear this in mind when considering the use of adapted projection lenses.
Assumption 3: Action-Stopping, Especially at Distance
Switching priorities again, let’s assume a different, but equally common, objective: distant action-stopping – sport, wildlife, etc – with a target size of 6,000px and shutter speed of at least 1/250s. The equivalence we’re seeking here is not that of aperture or image size, but speed – and the priority is likely mobility and reach.
If we take an ideal zoom lens for such purposes – on full-frame, 100-500mm – the GFX equivalent would be 150-750mm with a XXmm image circle – a monster. On APS-C, it’s a more manageable 65-330mm (rounded), and on Micro FourThirds, a positively pocketable 50-250mm. Smaller lenses for smaller formats with smaller image circles are decidely not equivalent in terms of price and size, and that endows them with real-world advantages.
In such situations, rapid autofocus tends to be a high secondary priority. It’s easier to make smaller lenses more responsive than larger ones, which again privileges smaller formats. Even the smallest is comfortably able to deliver 6,000px images with room to crop.
But what about the aperture disadvantage? In terms of depth of field, the ‘look’ of a 300mm f4 on full frame can be achieved by a 150/2 on M43, a 200/2.8 on APS-C and a 450/5.6 on GFX. A 300/4 lens for full frame (ie, Nikon FX) mounted on APS-C (ie, Nikon DX) remains a 300/4, but it will deliver the framing of a 450mm lens on full-frame, and a similar depth-of-field to a f5.6 lens on full-frame. However, because it is an f4 lens, it retains the action-stopping potential of an f4 lens – the shutter speed will be unchanged. A 135mm f2 lens designed for full frame becomes a much more useful combination of speed and reach when mounted on APS-C – with the motion-freezing potential of an f2 lens and the framing of a 200mm full-frame lens.
But what of noise? Assuming similar levels of technology and a similar pixel count (ie, a full-frame 24MP camera v APS-C 24MP camera), the larger format of course claws back its apparent one stop deficit by being able to shoot at higher ISO. But – in practice – with a requirement for ‘only’ 6000px and 1/250, the difference may not matter at all: in good light, it may be negligible: the difference between 1/500s and 1/1000s, or a difference in terms of colour and noise that is trivial. Similarly, at 400mm, the difference between the look of f5.6 and f4.0 may not be field-significant: both settings create heavily blurred backgrounds with excellent subject isolation.
We might imagine different assumptions, and each would change the ground rules. If you demand 8000px+ captures (for whatever reason*), or regularly crop hard, or work in low light, or demand an ultra-shallow DoF, or shoot only from a fixed position on a tripod, or have unlimited budget – all favour a larger format. And of course for some assignments there is no zoom too long or lens too fast. However, in most real-world scenarios, for most shooters, there are real advantages to smaller formats like APS-C and M43 when working with remote fast moving subjects.
Conclusions
If ‘equivalent’ is taken in its most practical sense to mean ‘as good, or useful, as . . .’ we have to set some objectives or ground rules to have a conversation.
The difference between APS-C and full-frame is in almost all respects one stop: one stop better light-gathering potential, one stop better image noise, one stop better capability to isolate a subject from its background or freeze it in time. Does one stop matter to you?
Similarly, the difference between medium format (or the dime store GFX version of it) and full-frame is one stop. But it’s more than that – because in almost all cases to realise that one stop advantage, you need to use adapted lenses that are optically compromised. Although APS-C relies on adaptation to be competitive with full frame in many cases, there we’re dealing with downsized image circles, not roaming the badlands of Zone D with a 100MP sensor.
Even with a Speedbooster, Micro FourThirds is a more significant two stops down from full frame. For stills shooting MFT has only one raison d’être: to be small, and correspondingly inexpensive. As APS-C and full-frame cameras have shrunk, and the iPhone has improved, the retail habitat in which MFT can survive has dwindled to the threshold of extinction. It just doesn’t compare. It’s only real photographic niche is undemanding safari-goers: the Panasonic 100-300mm offers an unmatched blend of performance, price and portability. The old, pocketable MFT cameras have had something of a deserved resurgence in 2024/25: perhaps OM System and Panasonic will smell what sells and pack desirable technology in a format you can pocket again, at a price that makes sense. They’re fun.
The 35mm format emerges as the only one that makes sense for photographers demanding high quality – unless you’re looking for 90% of its performance in a smaller form factor and 80% of the price – in which case APS-C remains a great choice for fast-moving remote subjects, and macro applications that favour large depth of field and long working distance. Those advantages are real. But 35mm does it all . . .
Apart from the extra bit of magic a larger sensor brings – by which I mean the unstressed, high dynamic-range vibe unmistakably generated by throwing a big light-gatherer at a scene. The difference is largely not about depth of field or subject isolation, but it is as great as the difference between 35mm and APS-C.