Lens tests

Lens tests Smartphones

On Samsung’s 0,0768 megapixels and other lies

Somehow, Samsung customers believe in megapixels and don’t believe in diffraction. Well, you know, there’s a sucker born every minute. Those of us who aren’t math-challenged know that megapixels don’t say anything and that the square root of them tells us that diffraction spoils everything. But it’s a lot worse than that.

Smartphone manufacturers invest enormous amounts of money, fighting an uphill battle they can’t win: the battle against physics. They made some progress by enlarging the sensor (but more isn’t possible unless smartphones get larger than cameras). The use of all kinds of software tricks, mostly consisting of noise reduction and sharpening also helped – somewhat. Yet in the end, you get a 12 MP picture that is still worlds apart from a decent real picture. Those smartphone pictures are great – for smartphone pictures. Once you start seeing the noise reduction artifacts and made up image details and smearing you realize those pictures are simply not useable an anything larger than a smartphone screen. Great for memories, but not for photography. And then we don’t even talk about the lack of lens choice and bokeh (because artificial bokeh is not high quality and only comparable to f/4).

First lie: 10 = 500

Now smartphone manufacturers know that, so they concentrate on what’s easier than to fight the laws of physics: they just invest in marketing. Huawei even got caught with their pants down when they used pictures made with a DSLR in their marketing, saying they had been made with a smartphone. Hey, a man gotta do what a man gotta do, right?

Samsung’s Head of Sensor Business Team, Yongin Park came up with a few new lies. The first is that the resolution of the human eye is around 500 megapixels. Bullshit.

When I measure it for my eyes, it’s about 10 megapixels. Depending on your criteria and acuity that it’s between 2.5 and 35 megapixels for your eyes but never 500. How do I measure it? Quite simply, by looking at the same test charts I use to test lenses. I look at the test wall I use to test a 50mm lens and then from the same distance and I get a reading comparable with about 50 lp/mm for a full-frame camera.

The eye consists of both one small spot, the fovea, with a relatively high resolution and a much larger area with a much lower resolution, so much lower that, in terms of megapixels, you can forget it. Now the fovea only has a field of view of between 1.5 and 2 degrees, this corresponds with a very long telelens of 1200 to 1600 mm! Peripheral vision – Wikipedia.

But since the movements of your eye are partially involuntarily, you get the impression you can see sharp over a larger view angle, as if the fovea were larger. This is not strange: when we talk about a lens that complies with your natural look of that the world, we mostly mention a 50 mm lens. Such a lens has a field of view of 40 degrees horizontally (47 diagonally). In practice it works as follows: when you look at a detail, you point your eye at it and you use the fovea. While reading e.g., you jump with your eye from word to word. The rest of your eye you use only to get a general impression and to see movements.

Now if  refer to Wikipedia for the visual acuity and calculate that back to the situation where you look at a distance of 5 m, you get 27 lp/mm, but for good eyes it’s about double of that and that’s the value I get for my bionic eyes after my cataract operation: https://en.wikipedia.org/wiki/Visual_acuity

That means that no matter whether you measure it or calculate it, you end up with a value of 10 MP.

But I can understand why Park lied about the resolution of the eye. His PR department needed urgently some tale around their new non-existing 600 MP sensor. (That’s not a real lie, but ist very strange to brag about a thing you haven’t done. It’s like me telling you that I’ll win the Noble prize next year and then continuing to brag about how smart Nobel prize winners are. First see, then believe.)

Second lie: 0.0768 = 108

Now back to the real lies. Why did Park need new lies? As I said, smartphones are all about marketing. So Samsung makes a very expensive phone with 108 megapixels, which makes pictures with … 12 megapixels. As you can see in https://www.techradar.com/reviews/samsung-galaxy-s20-ultra-full-review the iPhone 11 pro with only 12 MP makes better pictures than the Samsung with 108 MP. So why do they use this technique? Simple: to lie to the customer. The customer in his turn can lie to his friends he has a 108 MP smartphone.

But it’s even worse. In fact, this 108-megapixel camera only has 0.0768 megapixels. Just do the math with me. The Samsung has 100 x zoom, according to Samsung. Another thing to brag about isn’t it? Or just another lie. We start with 48 megapixels (that don’t look better than 10 megapixels, but ok, let’s give poor Samsung a break, they are in big trouble as we are about to see and they can’t count, which is quite a serious issue if you’re in the tech business). To get to 100 x zoom you have to crop 25 x. That means there will be 25 ^2 is 625 x fewer megapixels than we started with. 48 / 625 = 0.0768 megapixels to be precise.

Lies on top of other lies

But there’s another reason Park urgently needed some lies about eyes and cameras. Samsungs Vice Chairman, Jay Y. Lee, just got arrested. You want to know what he did? Lying. No, not about megapixels, but about stock prices, audit rules, and bribery. And the guy just came out of prison a year ago or so, for similar reasons!

I guess in marketing, if a thing like that happens, you have to create some other lies to make up for it. So, OK, the human eye has 500 megapixels, Samsung has a 600-megapixel sensor and it’s Galaxy Ultra makes 108-megapixel photos and has a 100 x zoom.

Now the truth

The truth is much more interesting and revealing than lies, as those among us who aren’t caught in a marketing bubble know. Let’s go back to the first lie, about the resolution of the human eye. If our eye has about the resolution of a smartphone, why is it that what I see is so much more detailed than what I see on a smartphone picture?

Just look at this detail from an iPhone XR picture. Yes, you do see small details. But if you look closely, you see that they don’t look natural. That’s because we only see high contrast details, the low contrast details are lacking. That’s what you get of course if you start tricking with information. If you’ve ever seen MTF graphs, you know that the smaller details get, the lower the contras gets. If you use sharpening, you just make the contrast higher, especially at the border of two lines. That helps with high contras details and even with coarse lower contrast details, but the smaller lower contrast details, that just haven’t been recorded, will not come back. That’s why a smartphone picture looks ok-ish until you look at it on a larger screen. And this example is even from an iPhone XR. Apple is very careful to not meddle too much with details, at least compared to other smartphones like Samsung.

Samsung is bragging about a sensor they don’t have yet. But just like Samsung I can tell you something about this non-existing sensor. It won’t make much difference. As you can see at https://www.tomsguide.com/reviews/galaxy-s20-ultra a sensor with native 12 megapixel makes better pictures than a 108 megapixel Samsung sensor. Why? Because of the laws of physics. The more megapixels the smaller the pixel pitch and the more sharpness you’ll loose from diffraction. As a rule of thumb, you can say that the maximum aperture you can use before resolution suffers, is about 1.5 x the pixel pitch in micrometer. Apple uses a pixel pitch of 1.4 micrometers, so with f/1.8 you’re about right.

Diffraction limitations

For all practical purposes, this is also the border. Using a smaller pixel pitch means, that diffraction will make your picture less sharp. So what you win by adding pixels, you lose by making them smaller from that point.

That is also why Apple iPhones with 12 megapixels make at least equally sharp pictures than 48 or even 108 megapixel smartphones from Samsung and the like.

Now you could argue, but what if I make the lens with a larger aperture? After all, diffraction is determined by the aperture (and the wavelength of the light, which you can’t change). That’s also the reason why smartphones don’t have an aperture: they operate already at the diffraction limit. So you could use a larger aperture, f/0.6 instead of f/1.8…

Yes you could – in theory. You should understand though that the current smartphone lenses are already making an enormous effort to be diffraction limited. The small lenses make use of extreme aspherical surfaces at all elements, what more can you do? Since most lens aberrations increase exponentially with lens speed (aperture) you won’t be able to solve this problem.

Well, OK, there is a solution. If you make a lens more complex, if you add elements to provide extra aberration correction, then you can create a diffraction-limited lens with a very large aperture. But the problem with smartphones is, that you don’t have the room to use lenses like that.

Sounds a little ironic, but if you want to use very small pixel pitches you’d better use a large camera with exchangeable lenses, something like a mirrorless full-frame camera. So that’s where the snake bites its tail.

As I told you; smartphone manufacturers are fighting an uphill battle against physics they can’t win. In the long run, even PR lies don’t change that.

Geen categorie Lens tests Nikon

Focus breathing and more

On www.quora.com, I got the request to answer this question:

Adam Palmer and 1 other person are looking for an answer to:
Why does the 70mm end of my Sigma 70-200 F2.8 looks so much more zoomed in than the 70mm end of my Sigma 24-70 F2.8? They’re both full frame lenses being used in my Nikon D7500 APS-C.

Here’s my answer:
Focus breathing plus accepted tolerance. The focal length is defined when focused at infinity. Yet all lenses with internal focusing change their focal length while focusing. (Zoom lens are almost always internal focusing, otherwise, they would need an enormous helicoid and get very large.) You have to imagine a zoom lens has a moving group lens elements for zooming, another moving group of lens elements for focusing and yet another moving group of lens elements to compensate for the focus changes while zooming (so to keep it sharp while zooming). I don’t know if you ever had two girlfriends or whatever at the same time (or whether your girlfriend or whatever had two you’s at the same time), but you can imagine that it makes things complicated. Same in a zoom lens.

In short: This means that the focal length gets shorter when getting closer. In the case of a 70mm that might mean it’s effectively 65 or even 60mm up close. It’s mostly not a big deal, it’s just one of the many consequences of lens design, which is one big tradeoff. Now I don’t know which Sigmas you are referring to, but the 24-70mm f/2.8 ART suffers from some focus breathing at the long end. Several iterations of Sigma’s 70-200mm f/2.8 too as far as I remember, and then also on the long end. So if you set both lenses to 70 mm, one will suffer from focus breathing a lot more than the other, since in one case 70mm is the short end, in the other, it’s the long end.

Another fact of life is that focal lengths do have some tolerances. 70 mm even at infinity, is never exactly 70 mm. It will more likely to be something like 67,6 mm or 72,4 mm. If your lens suffers from focus breathing, this is one of the ways to compensate for it, but sometimes it’s just the way a lens design turns out. There are also ISO tolerances here, so don’t start to measure your lens and hope to get your money back. And really, those are general things, all manufacturers basically have to deal with the same optical limitations in lens designs and then make their own tradeoffs.

If you own the Sigma Art, you will probably also notice the 24-70 is less sharp in the corners at 70mm. So keep that in mind and change to the 70-200mm while making pictures if you need the focal length and/or sharpness.

One last remark: the fact that you use a D7500, so an APS-C camera with those lenses, doesn’t change anything, as long as you use the same camera with both lenses. The camera crops the image 1.5 x but in both cases.

Canon Lens review Lens tests Nikon

New 70-200-zooms from Nikon and Canon and a superior 120-300mm f/2.8

Canon and Nikon are churning out new lenses for their mirrorless camera quickly now. All lenses for the new mounts have proven to be excellent, no surprises so far. Now we finally see the introduction of the respective 70-200mm f/2.8s. These lenses are very interesting because they are the most difficult to develop – in decent quality, that is. Telezooms have originally been a specialty for Nikon. The 80-200mm f/4.5 was the first zoom lens that was as good as primes, ‘the zoom that ends all other zooms’. The 85-250mm f/4-4.5 (1959) was even the first tele zoom lens in the world. By the time Nikon introduced the first 80-200mm f/2.8 Canon joined Nikon and has been able to offer the same quality.

But when Nikon introduced the 70-200mm f/2.8 FL, the third generation of 70-200mm f/2.8s, Canon didn’t really follow. They just reintroduced the second generation and changed the coating somewhat. So Nikon’s 70-200mm became the best 70-200mm you could buy.

Now we see both brands introducing a 70-200mm f/2.8 for mirrorless. And for the first time, we see a completely different approach. Canon designed a lens that used a feature we saw only in amateur lenses so far, a lens with an extending barrel. This construction was considered unfit for pro lenses, since if you bump against something with the lens, it might get misaligned because the barrel or the cams get damaged.

But apparently Canon gave this construction a real good thought and was able to make it quite sturdy. Lens Rentals writes: ‘The Canon RF 70-200mm has about the most robust extending barrel mechanism I’ve ever seen. There aren’t the usual three cams sliding about to move this barrel, there are three pairs of them, and each is very large and robust.’ When collapsed, the lens is also less than  2/3 of previous and comparable lenses and the new Nikon: 1070 g and 146 mm vs. 1440 g and 220 mm.

But of course, weight and size are only two parameters. The most important one is the optical quality and the second most important one is the price. Price-wise both lenses are in the same region as their precessors, the Canon a little more expensive, the Nikon even a little less. As for the optical quality: I wasn’t able to test either lens yet, but we do have the MTFs already. Manufacturer MTF’s can’t be compared directly, but in this case, we can find a way around this conundrum. We do have the MTFs of the previous version of the lenses of both Nikon and Canon and I have my own test results of those lenses. If you combine them, you can say a lot of those lenses, assuming that Canon and Nikon didn’t change the way they calculate MTFs in the last year.

So based on that the conclusion will be that both manufacturers did a great job – but a different job. Canon concentrated on making the smallest and lightest 70-200mm f/2.8 on the market, even with stabilization. Based on the MTF, the optical quality will be better than the previous one; somewhat – but not much – less than the previous Nikon 70-200mm f/2.8, the FL version.

Nikon did something completely different. Their 70-200 f/2.8 is almost exactly the same size and weight as the previous one and has stabilization too. So it should be better than that one, but… that lens already was the best in the market and is not even four years old. As unlikely as it may seem, Nikon succeeded in developing a lens that is a whole class above the previous 70-200. The MTF at 200mm looks better than the one of the 180mm f/2.8 prime, and at least equal to the MTFs of both 300mms f/4s, both of which are known to be very good lenses. Based on the MTF one would expect the Nikkor Z 70-200mm f/2.8 S to be the first 70-200mm that also delivers excellent results with converters. That would make the lens even more attractive.

On the other hand, you can’t use the F-converters on this lens. If a hypothetical Z-converter uses the same built principle as the Sony one, it will be very asymmetrical which isn’t good. So we’ll have to wait and see. There are not even converters on the Z roadmap yet. But then again Nikon also introduced a 120-300mm f/2.8 in the F mount. Of course, you can use that lens without any penalty on the Z cameras as well. The MTF at 300mm looks superior, better than the 300mm f/4s and at the level of the 300mm f/2.8 and 400mm f/2.8. So this lens will very likely be an excellent 160-420mm f/4, 185-510mm f/4,8 and a 200-600mm f/5.6 as well. It’s not cheap though. But there’s also a 200-600mm Z lens on the road map. It looks like Nikon owners soon have too many excellent lenses to choose from.

As for Canon: really nice to see a lens a compact and light 70-200mm f/2.8 of high quality. In the last couple of years, we’re seeing more and more lenses that only 10 years ago would have sounded like science fiction. Great times to be a photographer!

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