Basti's Scratchpad on the Internet
25 Mar 2019

On camera sensor sizes

A common internet wisdom about photography is that bigger camera sensors capture more light. So if you want to work in low light, you need a full frame camera, and a bigger sensor is always better. I have struggled with this a lot, though, because it doesn't make sense. Lenses can focus light on any surface, so why should the surface size matter?

The answer turned out to be… disappointing. Bigger sensors allow for larger (practical) apertures, and lower base ISO. But less noise for the same picture, is simply impossible with the same sensor technology. Because that's not how physics works. Let me explain.

Let's talk about three sensor sizes, full frame (FF), APS-C, and micro four thirds (MFT). For the sake of discussion, let's assume that these sensor sizes are always a factor of \(\sqrt{2}\) of each other, which is close enough to the truth. So FF is twice the area of APS-C, which is twice the area of MFT. Let's also assume that our hypothetical cameras at these sizes use sensors with the same resolution, and using the same technology. With that out of the way, what does it mean to use a smaller sensor?

If you shrink the sensor area by a factor of two, every pixels gets equally smaller, and receives less light (on the same lens). To fix this, and account for the different field of view due to cropping, we zoom out, dividing the focal length by \(\sqrt{2}\). So now a FF 35mm f4 lens will get the same field of view and brightness as an APS-C 23mm f4 lens, or a 17mm MFT f4 lens, all at the same ISO number. The only difference being, that due to the smaller sensor, MFT will be twice as noisy as APS-C, which is twice as noisy as FF. This seems like a clear win for FF, right?

As an aside, isn't it cool that we actually get the same brightness, as long as ISO and f-numbers are kept the same? That's what they are designed to say: Equal ISO and f-number means equal brightness! (But not equal noise, or, as we will see, equal depth of field).

Because here's the catch: Even though the f-number is the same, the physical size of the aperture is bigger on the bigger sensor! This makes sense, because to get the same brightess on a bigger sensor area, you need more light. And to get more light, you need a bigger aperture. This also means that the depth of field on the FF sensor is twice as big as on the APS-C sensor, which is twice as big as the MFT sensor.

So let's account for that, too, and give each camera a lens with the same physical aperture size as well as field of view, and stop down ISO to account for the increase in brightness: FF 35mm f4 ISO 1600 then becomes APS-C 23mm f2.8 ISO 800 and MFT 17mm f2 ISO 400. These combinations now actually have the same field of view, same brightness, same depth of field, and, you guessed it, same noise. If you account for field of view, there is no advantage to FF whatsoever. You can get the very same picture on a big sensor as on a small sensor, the only difference being how much you are willing to carry and pay for it.

OK, that's not quite true: You can get FF lenses at f1 (equivalent to f0.7 on APS-C or f0.5 on MFT), which are just not available on smaller sensors. But have you used such lenses? At this point, the area in focus is literally razor-thin, and focusing becomes terrifyingly difficult. You might also notice that wider-aperture lenses are generally bigger. They have to be, to capture more light. By the same token, an f1.4 APS-C lens will be the same size as an f2 FF lens (because it is in fact mostly identical). And FF offers smaller base ISOs. If you need the minimum amount of noise, ISO 100 on FF would be equivalent to ISO 25 on MFT, which you just can't get, there.

TL;DR: Bigger sensors afford bigger apertures, with all their associated downsides. But they do not magically reduce image noise (everything else being equal). Also, cameras are surprisingly complex beasts.

Tags: photography
13 Mar 2019

Learning about Photography: Sunstars

Normally, when you take a picture of something too bright, you get bloom: An all-consuming brightness that plunges everything around it into pure whiteness. Ugly.

But if the light source is reeeally tiny, and your aperture is teeeensy as well, you get something else: sunstars

sunstar.jpg

This particular sunstar has fourteen corners, and therefore comes from a seven-bladed aperture (in my Fuji XC 16-50). It happens because tiny apertures are not perfectly circular any longer, but instead, in my case, septagonal, and therefore bloom more in some directions than in others. The effect is kind of beautiful.

In this picture, the sun was just barely peeking into the edge between the tree and the building, and my aperture was set to its smallest setting, f22. I actually wanted to capture the raindrops on the branches, which I largely failed at. In the end, the picture didn't turn out very pretty, but at least I got some fine sunstars!

Tags: photography
24 Feb 2019

What I learned about Amateur Photography

I am an amateur, as in "lover of", photography. I love cameras as tactile devices, I love how photography makes me consider the world as art, how that little viewfinder can reveal unknown beauty in well-known places or people. And I love looking at my photos, and remembering vacations and meaningful moments. For me, photography is about finding beauty, and capturing memories.

However, most of the writing on photography seems to be focused not on my needs, but the needs of professional photographers: A super competitive field of visual artists who compete on image quality and novelty, and use crazy and expensive gear. I have found many of their lessons not applicable to my amateur needs, or even actively detrimental:

Embrace the noise

Many pros limit their ISO numbers, because high-ISO noise is ugly. Which it is. But you know what is even worse for an amateur? Not having that picture of my baby, because it was too dark.

So I set my ISO to unlimited, reduce my shutter speed and aperture so I actually have a chance of capturing my fast-moving toddler. And embrace the ensuing noise. Some of my favorite pictures look unbearably noisy on my 4k screen, but look just fine when printed, or on a smartphone (the two most important mediums in the world). Because of this, I find noise reduction rarely worth the effort. Color heavy noise reduction works ok, but anything else looks worse than the problem. I vastly prefer a sharp, noisy shot to a mushy denoised shot with no detail.

Step it down

Another common Pro argument: Wider apertures are better. Which they are, at capturing light, and blurring the background. But as an amateur, a wide-aperture super-shallow depth of field just makes me miss shots. At f1.8, the area in focus is barely a few centimetres deep. I missed too many shots because I accidentally focused on the nose instead of the eye. So, in the absence of studio lighting, and arbitrarily many retries, I prefer to step it down and live with the noise, if need be.

As a fun corollary, all those fancy prime lenses with crazy-wide apertures, they are simply wasted on me. Anything beyond, say, f2.8, is not something I need to spend money on. Also, lenses are noticeably sharper when stepped down! I have been disappointed with the sharpness of a number of shots because I forgot to step it down. Nowadays, I typically shoot at f5.6 or f8, and only go wider if I actually need to, because of lack of light, or if I specifically want a blurry background.

Wide-ish lenses are easier

I wondered, for a long time, why pros seem to like long-ish lenses for portraits: The answer is, because longer lenses have a shallower the depth of field (for the same f-number), and pro photographers love their blurry backgrounds. But as I said before, that is not for me.

Instead, I prefer wide-ish lenses. If something is too small on a wide-ish lens, it is usually no problem to get a bit closer or to crop afterwards. If something is too big on a long lens though, backing off is often not possible, and you miss your shot1. Plus, wide-ish angles don't blur as much from shaky hands, and are more compact. They often focus more closely, too, which is a huge bonus if you want to take pictures of a toddler.

I have tried, unsuccessfully, a 50mm and 35mm prime (APS-C). Now I own a 27mm pancake prime, which I find perfect: long enough to get nice portraits, but still wide enough to capture a landscape.

Be careful with super-wide angle lenses, though. Even though they are a ton of fun, I have found anything below 16mm to be very difficult to use effectively. It's just too easy to get that fisheye-distorted look, especially near the sides. That distorted look, by the way, is caused by being too close, not by lens distortion. The same thing happens if you take a longer lens or a cell phone and get too close. Just don't do that.

Gear

Pros use the biggest sensor they can get, to get the best image quality possible. But that also makes everything else much more cumbersome: Bigger sensors mean bigger and heavier bodies. And bigger and heavier lenses. And shallower depth of field (see above). And smaller focal ranges, hence more lens changing. And, not least of all, much, much, much higher prices. It is not for me.

To some extent, the same goes for different quality levels: Personally, I have found entry-level APS-C mirrorless interchangeable lens cameras a good compromise. These entry-level plastic lenses and cameras are usually smaller, lighter, and cheaper than their higher-end brethren, but compromise on robustness and aperture sizes (e.g. Fuji X-E2 375g/€250 + Fuji XC 16-50mm, 195g/€150 vs. Fuji X-T1 450g/€250 + Fuji XF 18-55mm, 300g/€250 vs. my old Nikon gear). And for my everyday camera, I' take a smaller, pocketable camera over a "better", bigger one any day.

Haptics are important, too. I have seen great cameras and lenses that just didn't feel good in my hand. Which meant I wouldn't ever take them with me, and wouldn't take any pictures with them. I now go try stuff in the store before I buy anything. This has talked me out of a number of unnecessary purchases, internet consensus notwithstanding.

And finally, I buy used gear. Cameras and lenses depreciate about 70% within the first two years, without losing any quality. A great camera from two years ago is still a great camera, but costs a third of the original price, and can be resold without loss. And is better for the environment. Win-win-win.

TL;DR

I have found many "common" rules about photography useless for my amateur needs. I have found cheap, plastic, used gear more useful than pro gear. I have found noisy, small-aperture pictures to be better at capturing important memories than clean, "professional" ones. I have found haptics, size and weight to be much more important than ultimate image quality (within reason).

The funny thing is, you don't find this kind of information on the internet, since most review websites seem to focus on the professional viewpoint, even for gear that is clearly meant for amateurs like me.

Footnotes:

1

You need to back off much farther on a long lens than you have to move closer on a wide lens.

Tags: photography
06 Jan 2019

Books of 2018

There is no other media more immersive to me than reading. When I read, I dive deep into another world, and seize to perceive the reality around me. It is my escape from the everyday stresses of living in the modern world. Reading is truly sacred to me. So here are my favorite pieces of writing of 2018:

Shadow Divers

shadow-divers-cover.jpg

This is a book about deep wreck diving. I am not interested in wrecks, or diving. Nevertheless, no book gripped me as hard last year as Shadow Divers. At first, I was a bit thrown off by the writing style, and thought it dramatized things too much. But I just couldn't put this book down. There were times when I surfaced from reading with a distinct feeling of having been there, of having touched that menacing shipwreck at the bottom of the ocean.

By the end of it, I was entirely engrossed in the story and its characters and the history of the mystery wreck. And then, in the epilogue, I learned that what I had thought embellished at first was actually meticulously researched and not overdramatic at all.

And best of all, my favorite podcast, Omega Tau had an interview with the main protagonist of the book, which is just fascinating!

The Shortest History of Germany

german-history-cover.jpg

This book is a strange choice to put on my list of books, because I didn't like it too much. I found it offputting which parts of history the author emphasized, and which parts he skipped. Apparently, the two world wars did not bear mentioning. The book paints a strangely specific west-vs-east map of Germany, which is not without merit, but surely not the whole story. And worst of all, I really didn't care for the writing style at all.

But when I look back on 2018, this book has stuck with me. Never mind its shortcomings, it has given me a map of Germany's history that I can fit other pieces of knowledge into. And that makes it valuable to me.

And then there were (N-One)

n-1-cover.jpg

I love short stories. And this one is just brilliant. It is by Sarah Pinsker, about Sarah Pinsker, and all Sarah Pinskers from neighboring parallel universes. Every character in this book is a Sarah Pinsker. And all of them agree, Sarah is no murderer. Yet, one of them has been found murdered.

I won't spoil more of it, just head over to the Uncanny Magazine and read it for yourself!



Graphic Novels

For years now, I have struggled to find graphic novels that speak to me. I usually find the drawing style off-putting, and would have preferred a more fleshed out novel instead of a shallow graphic novel. But this year, I found two brilliant graphic novels that I loved dearly:

Maus

maus-cover.jpg

The half-auto-biographical narrative of a survivor of one the Nazi concentration camps. The novel juxtaposes the author's struggle to interview his father about his past, and thereby shows both the cruelty of the father's experience, and the man that this experience created. Both of these perspectives add weight to the unspeakable nastiness of the Holocaust.

But beyond that, it is also a story of humanity, struggle, and the small moments of joy amidst all the terror. Truly a masterpiece of a book.

Nimona

nimona-cover.jpg

In sharp contrast to the previous book, Nimona is just plain fun! Nimona is a teenage girl, and a shark, and the sidekick of Balister Blackheart, the biggest name in Supervillainy. And if you haven't guessed it from this description, it is wacky, and funny, and uplifting, and just… fun!

You can read the first three chapters online, and then you'll want to read the rest, too. It's just too much fun!

Tags: books
08 Nov 2018

Cool Python Libraries: TQDM and Resampy

In my recent post about appreciation for open source software, I mentioned that we should praise our open source heros more often. So here are two lesser-known libraries that I use daily, and which are unabashedly awesome:

TQDM

TQDM draws text progress bars for long-running processes, simply by wrapping your iterator in tqdm(iterator). And this, alone, would be awesome. But, TQDM is one of those libraries that aren't just a good idea, but then go the extra mile, and add fantastic documentation, contingencies for all kinds of weird use cases, and integration with notebooks and GUIs.

I use TQDM all the time, for running my scientific experiments and data analysis, and it just works. For long-running tasks, I recommend using tqdm(iterator, smoothing=0, desc='calculating'), which adds a meaningful description to the progress bar, and an accurate runtime estimate.

Resampy

Resampy resamples numpy signals. Resample your data with resample(signal, old_samplerate, new_samplerate). Just like with TQDM, this simple interface hides a lot of complexity and flexibility under the hood, yet remains conceptually simple and easy to use.

But beyond simplicity, resampy uses a clever implementation that is a far cry better than scipy.signal.resample, while still being easy to install and fast. For a more thorough comparison of resampling algorithms, visit Joachim Thiemann's blog.

Tags: python
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