Physics really works out such that the smaller you make camera sensor, the smaller you can make the lens. Full-frame lenses tend to be markedly bigger for equivalent quality compared to, say, APS-C lenses.

However, due to physics there is also no working around the quality issues of a small sensor. Photosites get less light and produce more noise, and automated noise suppression costs detail and sharpness.

I wonder whether tiny lenses of equivalent sharpness and clarity as their larger equivalents would be much more expensive or impossible to produce (sure, less material, but much finer precision required), but it probably doesn’t matter because the tiny sensor already loses enough sharpness that better lenses won’t contribute much.

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croemer 6 days ago | parent | next [-]

> Physics really works out such that the smaller you make camera sensor, the smaller you can make the lens.

At some point the wave-like nature of light starts to bite. Can't really go much smaller than a micron per pixel. So a millimeter sized chip gets you 1 megapixel. 50MP mean ~7mm. (back of the envelope caveats apply)

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meatmanek 6 days ago | parent | prev [-]

> Full-frame lenses tend to be markedly bigger for equivalent quality compared to, say, APS-C lenses.

Only if you define quality as field of view.

For light-gathering ability and background separation/bokeh, you need a lower f/number on APS-C than on full-frame to be equivalent: A 35mm f/1.2 lens on a 24MP APS-C sensor will take pictures that look nearly identical to a 52.5mm f/1.8 lens on a 24MP full-frame sensor. (Assuming crop factor of 1.5.) Both will have an aperture size of 29.17mm (= 35mm/1.2 = 52.5mm/1.8), will capture a 37.9° x 25.8° FoV.

Almost all important properties of lenses are determined by field of view and the aperture diameter: Amount of light gathered, background blur, diffraction, and weight.

The illumination-per-area on the full-frame sensor will be 2.25x lower, but the area of the sensor is 2.25x larger so it cancels out such that both sensors will receive the same number of photons.

Background blur is determined by aperture diameter, field of view, and the distances to the subject and background. Since the two lenses have the same aperture size and field of view, you'd get the same amount of background blur for a given scene.

For many lenses (particularly telephoto lenses), the size and weight are primarily determined by the size of the front element, which needs to be at least as big as the aperture. For wide-angle lenses, you start needing a front element that's significantly wider than your aperture for geometry reasons -- the subject has to be able to see the aperture through the front element, so that relationship breaks down.

(Also with lenses where focal length << flange distance, you start to need extra optics to project the image back far enough. This can mean that a wide-angle lens can be more complicated to build for APS-C than for full-frame on the same mount. Take for example the Rokinon 16mm f/2 at 710g / 87mm long versus the Nikon AF-D 24mm f/2.8 at 268g and 46mm long. This isn't relevant to phone cameras, since those don't need to fit a moving mirror between the sensor and the lens like SLRs do. Phone camera makers can put the lens exactly as far from the sensor as makes sense for their design.)

Slow telephoto lenses for DSLRs are pretty much the only place where crop sensors have an advantage. DSLR autofocus sensors generally need f/5.6 or better. Thus, for a given field of view, you need a bigger aperture + front element for the full-frame lens than the "equivalent" crop-sensor lens -- e.g. a 300 f/5.6 with its 53.6mm front element is going to be heavier than a 200 f/5.6 with its 35.7mm front element. However, as mentioned above, the 300 f/5.6 on a full-frame camera will gather 2.25x as much light as the 200/5.6 on the APS-C sensor. Mirrorless cameras can typically autofocus with smaller relative apertures. This is why you see Sony selling an f/8 zoom and Canon selling f/11 primes for their mirrorless mounts -- this sort of lens just wasn't possible on DSLRs. On mirrorless, you could have a 300 f/8.4 full-frame lens that would be truly equivalent to the 200mm f/5.6 APS-C lens.

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vladvasiliu 6 days ago | parent [-]

You're absolutely right, but what's depressing is how few people understand this. I'd say the problem with your point is that it's too practical and involves people going out and trying to produce some artistic expression.

Most people enjoy chasing measurable specs and don't stop to understand what they're actually doing. So they'll go compare a 4/3 sensor's output at iso x to a full frame sensor at the same iso. They won't stop to think about what they're trying to achieve. If they want the same depth of field, they won't be able to use the same aperture. So, out in the field, something has to give. Either lengthen the exposure or raise the ISO. If we're talking high ISOs, you probably can't shoot much slower, so higher ISO it is. Differences are then much less shocking.

The other extreme is people chasing paper-thin focus, which, I guess, isn't as easy to obtain on smaller sensors. Yet, for some reason, they won't go to a larger format, either...

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Espressosaurus 6 days ago | parent | next [-]

It's a market problem. If I could get the lenses I wanted in APS-C format, I'd have an APS-C camera as my main camera. Instead the market has chosen for full frame to be the main place investment is done in, so I get a full frame camera since the APS-C cameras and lenses are second-class citizens (not true for Fuji, true for Canon, Nikon, and Sony).

Medium format explodes the cost and again, the lenses I want aren't even available.

So you go for what you can get, given the marketplace and also given the lens system you have bought into.

I doubt anyone is going wildlife shooting with a large format camera, for example.

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tristor 6 days ago | parent [-]

> I doubt anyone is going wildlife shooting with a large format camera, for example.

Not with true large format, but with the new Fuji medium format cameras it's starting to become reasonably possible to do faster work like wildlife at larger format sizes. The main issue remains, which is sensor readout speed, but the technology has gotten so much better that you can get results with things like birds-in-flight that are comparable to a FF DSLR camera from 10 years ago, with MF now, as far as speed, but at 3x-5x the effective resolution.

Cost is still prohibitive though, I recently upgraded and really considered the new Fuji 100MP MF line, but ended up with a Nikon Z8 in the end for wildlife. On my next iteration, I'll probably bite the bullet and go MF. If I could double the resolution and get similar speed, it'd be worth it, IMO. Especially at the sizes I typically print

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dagmx 5 days ago | parent [-]

I’d also just add that Fuji has some of the worst autofocus on the market right now. Going between my Fuji and Sony bodies, I realized how much I took my Sony AF for granted.

If Sony would make a MF body, I’d be all in.

	▲	strogonoff 4 days ago \| parent [-]
		I immediately felt the heft after switching to FF, and that while specifically choosing lighter and smaller used primes. Do light & small primes exist for MF at all? Can you realistically casually carry an MF setup with a few lenses, or is that basically a car-only ordeal (and good luck flying commercial with it)?

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strogonoff 6 days ago | parent | prev [-]

> The other extreme is people chasing paper-thin focus, which, I guess, isn't as easy to obtain on smaller sensors.

Really? I used a nice longer (maybe 80mm equivalent) lens on an APS-C system a while ago, and it gave very shallow DoF while being much lighter and more practical (cheaper, etc.) compared to what I can find for a full frame. Not going to look up the physics but I was under the impression that shallow DoF is easier on smaller sensors (I don’t mean phone small, just crop small).

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vladvasiliu 5 days ago | parent [-]

Sure. But now go compare a FF 80mm with the same aperture as your 50 or similar lens used on the APS-C. The depth of field will be shallower on the FF.

> I was under the impression that shallow DoF is easier on smaller sensors (I don’t mean phone small, just crop small).

It's the reverse. These things are continuous. There's no reason for it to be easier one way, then all of a sudden stop and become increasingly difficult. Otherwise, there would be no need for shenanigans with "portrait mode".

My iPhone 14 pro's main camera is an equivalent 24 mm f/1.78. It has way much more in focus than my m4/3 12/2 (also a 24 mm equivalent).

	▲	strogonoff 5 days ago \| parent [-]
		> But now go compare a FF 80mm with the same aperture as your 50 or similar lens used on the APS-C. The depth of field will be shallower on the FF. I did not see it becoming shallower after moving to FF, but then I was using different lenses on FF (cheaper older manuals). That probably sums up what I mean. Sure, when you account for crop and adjust for the same framing then DoF will in fact be deeper on the crop practically. However, even more practically, there are small and affordable f1> lenses made for crops, whereas the brightest 100mm I used on FF is f2.8 or so because going lower they are really big and/or really expensive. So, for equivalent cost/size/weight, you may have easier time getting shallow DoF on a crop if you buy lenses specifically for crops (which admittedly limits your choice of glass).