I’ve been thinking how to explain photographic optics to beginners, because the explanation is usually something like this: the bigger the sensor, the lesser the depth of field, the closer the point of focus the lesser the depth of field, the wider the aperture the lesser the depth of field, the bigger the focal length the lesser the depth of field. So, depth of field is inversely proportional to focal length, sensor size, and aperture, and directly proportional to focal distance.

But what exactly is the depth of field?

To understand depth of field, you need to understand that only a single point in the image, the point of actual focus, is perfectly sharp. Everywhere else, the lens diffuses a ray of light into a circle, called the “circle of confusion”. If the circle of confusion is small enough to fit into a single pixel on the sensor, basically if its diameter is less than the pixel pitch of the sensor, we perceive it as “sharp”. However, what it actually looks like can be mathematically represented as a parabolic function:

Let’s say that the x axis represents the distance from the focal plane of the sensor. 0 is the point in focus. The y axis represents the diameter of the circle of confusion, and 0 means that it is in perfect focus, and y is a mathematical point. If it’s below 1, it means it is perceived as sharp because the diameter of the circle fits within one pixel. So, everything between 0 and 1 is perceived as sharp, and as the radius grows, the picture starts getting blurry. Let’s illustrate this photographically:

As you can see on the asphalt, there is a tiny strip of sharpness, and everything before and after is blurry, progressively with the distance from the point in focus. At the most distant parts you can clearly see the circles formed as the rays of light are defocused. On the strip in focus, it appears that more than just a single point is in focus, because for some time the defocused circles are small enough to fit within a pixel on this level of magnification. This strip that is perceived as sharp is called the depth of field.

The shape of the circles of confusion beyond the depth of field is called “bokeh”. The angle of the parabolic function defines the amount of bokeh. If the parabolic function is steep, it means that only the things very close to the point of focus are sharp, as everywhere else the circle quickly grows into huge “bokeh balls”:

If the function is “shallow”, it means that it is possible to create an illusion that the entire image is sharp, from the closest visible point all the way to the horizon, because the diameter of the circle of confusion at the desired magnification of the output is still less than 1, or close enough not to matter:

So, in effect, the perceived sharpness beyond the point of actual focus is an artifact of magnification and photographic trickery. If you magnify enough, you’ll see that almost nothing is ever in perfect focus.

Now we get to the useful parts. If you shorten the focal length, you reduce the angle of the parabolic function, making it almost parallel to the x-axis. The same happens when you reduce the sensor size, but the reason is trivial – you need lesser actual focal length to produce the same field of view on a smaller sensor, so it’s still merely a function of the focal length. When you stop down the aperture, you force light to go through a smaller circle, reducing the cone of light that produces a mathematical point when in focus, or disperses more strongly when not. In theory, only a picture formed by perfectly collimated light source, meaning parallel rays of light, would be in perfect focus, meaning no light cones, but laser rays; also, this means that a pinhole camera, or a camera with a lens stopped down so extremely that it becomes a pinhole, would form a perfectly sharp image with an infinite depth of field. However, as the aperture becomes smaller, the rays of light interfere with its edges, which blurs the image, which means that such a perfectly sharp image would also become perfectly blurry due to diffraction. So, since, the f-stop is a function of the focal length, the absolute aperture is merely a function of the focal length as well, which means that we managed to reduce three parameters to one – sensor size, aperture and focal length are all functions of the absolute focal length, which leaves distance from the focal plane. However, if you imagine the light cone formed by the object in focus, it is obvious that the angle of this cone becomes larger as the object is closer, and smaller as it is farther. This means that the rays of light become closer to parallel as we focus closer to infinity, which produces an effect similar to stopping down the aperture. This also means that we managed to reduce all our parameters to the angle of the light cone, and diffraction as the second limiting factor that literally interferes with sharpness.

Sure, there are other optical effects that play a role – for instance, the difference in sharpness away from the centre of the circle that the lens draws, and within which the sensor is inscribed, the difference in refraction of various wavelengths of light, which creates chromatic aberration, the difference in the amount of light that falls on the edge of the circle relative to the centre, which defines vignetting, and so on. There are many optical defects that detract from the ideal appearance of the image, and although sometimes those optical defects can look interesting or charming, I personally subscribe to the opinion that less is more when it comes to defects. The only optical defect that I actually intentionally introduce to images at times is vignetting, because I think it focuses attention to the centre of the image, which is usually useful.

In any case, the difference between optical defects and optical laws is that the optical laws are something that will determine what happens with every single lens of a certain aperture and focal length, when projecting a circle of a certain size upon the focal plane. Optical defects, however, are what differentiates lenses of superior and inferior optical design and quality. This means that all telephoto lenses with wide aperture will create very shallow depth of field, but the good lenses will be tack sharp in the point of focus and devoid of significant defects, while bad lenses will be lacking in sharpness everywhere, and will introduce all kinds of optical defects, such as field curvature, low resolution, chromatic aberrations, colour cast and so on. Complexity of design and manufacturing tolerances that make a difference between bad, good and great lenses can be really extreme, which is reflected in the price; your tolerance for optical defects might vary. Unlike defects, the optical properties that are defined by focal length, circle size and aperture are universal, and don’t vary with lens design and price range.

I recently talked a lot about photographic equipment, and my annoyance with all kinds of nonsense I’ve recently seen on the Internet about how Leica or Fuji is “special” because it has “that something” or encourages you to take pictures with how cool it is and how you form a synergic relationship with it, unlike Sony or Canon which is “just a tool”. I get it, it’s a real phenomenon and I’ve personally experienced it, and what’s interesting is that it literally never happened with the kind of equipment you would expect. It didn’t happen with Leica, which is the first camera I shot with, or Minolta, which is probably the only camera brand I’m sentimental about because it was the one I used for, well, decades. It wasn’t Olympus E-1 which was justifiably praised as ergonomically great. It wasn’t the Canon 5d.

Fuji Astia 100F, EOS 3, EF 85mm f/1.8

It was Canon EOS 3, the camera that was widely criticised for being “too electronic”, with lights and whistles and what not. That was the first camera with which I experienced camera completely vanishing from the process of taking pictures. I didn’t have to thumb-wind film like I did with Minolta X-300, which made me remove my eye from the viewfinder, since I use the left eye to focus (I’m highly ambidextrous, but I use left parts exclusively for certain things, and right parts for others, for instance I use mouse with my right hand and touchpad with my left, and so on), I could do absolutely everything on the camera without breaking eye contact with the subject through the camera, and the autofocus was scanning my eye with a laser to decide what I’m looking at and choose the appropriate AF point. Also, everything was extremely fast to the point of being instantaneous and seamless – AF, film transport and so on. Unfortunately, I got it about the time when film was solidly on its way to history, in 2006, but it was absolutely the best camera I ever used at that point, film or digital. Returning to the 5d felt like going down at least one quality class, but it was digital and the pictures it produced were amazing, so I didn’t complain.

The worst experience I had with cameras recently, on the other hand, was with the Mamiya 645. I shot a few rolls of film with it, decided it’s heavy, clunky, required lots of adjustments on my part and acquiring muscle memory in order to be proficient, and it was a poor fit for my style. I returned to the Olympus E-PL1, which is also an ergonomically awful camera because it doesn’t have a viewfinder and autofocus is horrible, with a feeling of relief because it was so much better than the Mamiya, and the image quality of the Olympus was actually as good with my Epson 4990 flatbed scanner. The problem with those bad cameras is that they make the experience all about themselves. It’s no longer about you, what you see or feel, but about what the camera can do, what it’s good at, how heavy it is, how much of a nuisance it is, and I think it’s exactly that which eventually forms that Stockholm syndrome relationship with equipment, which is hard to use, makes you work hard to adjust to its quirks and nonsense, and is also expensive, so when you actually manage to jump through all the hoops, you get an endorphin rush as if you achieved something.

I recently took a picture with the Sony A7RV and the FE 35mm f/1.4 GM in sunset, and it’s one of my recent favourites because of how well it captures the feeling of clarity and peace, of a day coming to its end:

Sony A7RV, EF 35mm f/1.4 GM

I saw the light, the colours and the motive, framed the composition, pointed the AF to the plane with the branches and some leaves and made it somewhat parallel to the sensor in order to get the dept of field at f/1.4, and squeezed off the shutter. The camera was out of the way and just did its thing to a degree I haven’t experienced since EOS 3, although A7II was also similar, barring autofocus which is a nuisance. I think EOS 3 and A7RV actually do the things people ascribe to Leica and Fuji – they get out of the way and become an extension of your will and intent to the point that you lose awareness that you’re using a camera at all. It’s just that they don’t put you through boot camp and try to break you in in order for you to be allowed to just take the pictures you want to take without putting the damn camera on a shrine because you dedicated half your life to learning how to work it. I think that’s why the hipsters hate certain cameras and brands and say they are “just tools”. It’s because those cameras don’t lock them up in a basement and beat them until they call them “daddy”. They just do what you ask them to, and if the results aren’t good, you don’t get to say “ah, but you don’t know how many hoops I had to jump through in order to get that”. 🙂

Every single photo I took with EOS 3 was incredibly easy to take, and regardless of the fact that I got to shoot only a few rolls of slide through it, on those rolls was an inordinate percentage of my all-time favourites. Sony seems to be very much like that. It just gets out of the way and does its thing, and this allows me to get into my thing. And, believe it or not, “my thing” isn’t dealing with camera’s bullshit. It’s capturing the moment and the feeling.

One of the most frequently asked questions, regarding photo equipment, is which brand to get, which is the best, and what to avoid.

To put the obvious thing aside, my knowledge about photographic brands is limited to what I’ve used, and what I’ve seen others use. Of the major brands, I never used Nikon, Hasselblad, Panasonic, Fujifilm, Pentax and Leica. Sure, I technically used a very old Leica from the 1940s to shoot my first roll of film, and I used a Nikon D80 a few times but no, for all intents and purposes I haven’t used those and I don’t know much about them. With Nikon, the reason is that they publicly stated that they will never make a 35mm full frame camera, exactly at the time when I was deciding between Canon and Nikon, so I went with Canon. Of course, Nikon announced a 35mm digital camera soon thereafter, but by that point I completely lost any interest in them, since they were for most intents and purposes identical to Canon, and it’s one of those situations where you need to pick one and stick with it.

My main suggestion would be to see what your intentions are, first. If you want to get something basic to learn photography, get something used and cheap in the category you’re interested in, learn for a while and then you’ll know more about what you want to do. Don’t worry about getting “the right brand” initially, because there’s no reason why you should stay within the same system if you only have one camera and one lens. However, if you are really into it, the best advice is to see what the professionals are using as their bread and butter system, and just get that. Main brands have the greatest availability of new and used equipment, the used marketplace is very active and if it’s a system like Canon EF, that’s producing lenses in the same system since 1987, there will be abundance of high quality used equipment that’s fully compatible. For instance, the earliest Canon EF lenses work great on the new RF bodies with the Canon adapter; there are no compatibility issues. This makes Canon RF an excellent modern system to get into, because the selection of glass is extremely deep. With Sony, the situation is theoretically worse because the adapters for Canon EF glass aren’t fully compatible, but there’s a wide selection of 3^rd party modern glass from brands such as Tamron and Sigma, and almost anything else can be adapted to Sony, so the selection of glass is almost endless.

Avoid marginal and new brands. Anything non-mainstream means poor availability of everything, and high prices. Also, avoid “luxury brands”, the ones that should belong in the LVMH group; stuff like Leica, Hasselblad, Zeiss and so on. Have in mind that Schneider-Kreuznach recently had Rokinon/Samyang make lenses for their brand, and “Zeiss” lenses are produced by Cosina and Tamron. Hasselblad had their H series of digital cameras and lenses produced by Fuji, and they have recently been bought by DJI, the Chinese drone company. Leica is more-less married to Panasonic. So, yeah, that’s what you would be buying if you’re a sucker for old German and Swedish names from last century. You’d be getting Cosina, Tamron, Fuji or Panasonic.

My logic is that quality is where the money is, and money is in the main stream. The most main-stream companies can afford the greatest budget for development of lenses and cameras, because that’s what people are actually buying. If you think some marginal boutique brand can afford the engineers, equipment and the patents of a Sony or a Canon, you’re kidding yourself. The reason the boutique brands are expensive isn’t because they are better, it’s because they have to be, because they don’t have the economy of scale. You’re not paying for quality, you’re paying for development and manufacturing costs divided by the number of expected sales. Zeiss is literally not making anything Tamron or Cosina couldn’t produce, because guess who’s actually manufacturing their designs. I know people like to delude themselves into loyalty to small brands, thinking it’s a competition between handcrafted gems made by skilled artisans, vs. some nameless faceless corporation, but it doesn’t actually work like this. How it works is that Sony sees that there’s a market, and then just hires the best people in the business, acquires everything relevant from Minolta and Olympus, and then has the budget and the market to produce some of the most wonderful lens designs I’ve ever seen, stuff that merges art, science and the highest optical tech. The lesser companies will just be unable to afford retaining the best optical engineers, so in the end, it’s the big guys who will end up with the nerd artisans designing the most insane glass. Also, you’ll be getting a honest product for a honest price, not marketing bullshit worthy of Rolex or LVMH.

Sure, it adds to the mystique of a lens if it’s branded Zeiss, Leica or Hasselblad, and since photographers create art they want to believe that some unique properties of the glass helped create it, but honestly, a lens is what it is, regardless of the brand. It has objective, scientific and technological properties that can be tested. I don’t even mind lenses being expensive if the price is backed by quality. I just prefer to pay for the quality of the lens, not the quality of some marketing department doing the branding.

Image produced by absolutely nothing fancy.

Also, don’t buy into the bullshit about main stream brands producing confectionary images, that look “artificial” or “plasticky”, while the boutique or “art” brands produce “film-like” or “genuinely artistic” results. It’s complete nonsense. What the main stream brands produce is high quality gear for honest money, and what you’ll do with it, whether it will be plasticky nonsense or genuine art, that’s up to you. Some people say “digital” as if it’s a derogatory thing, and they say “film-like” as if it’s praise, but honestly I’ve seen so much “film-like” ugly trash, and so many absolutely beautiful, artistic digital images, that I don’t even know what they mean by all that bullshit. If you think Michelangelo had super-special artistic hammer and chisel with which he created his sculptures, then you’re an idiot. What cameras and lenses need to be is reliable, well designed and well made. They need to have technical properties required for the desired application. Whether the result is art, that’s up to the photographer.