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  • Writer's pictureTomasz Budzyński · Fotosceny

DSLR vs Mirrorless

What you should know about DSLR and mirrorless cameras

by Fotosceny

Table of contents:

1. Introduction

Probably every photographer, whether professional or amateur, trying to buy a new camera, asked themselves this question - what kind of camera to choose. This question is quite old and it is not the intention of this article to answer it - a whole bunch of hints and comments can already be found on the Internet. My intention is not to point out which technology is better and which is worse - rather to share some observations and experiences, that I've come across either when trying to buy a mirrorless camera or encountered after buying it - after starting my experience with the new technology. I'll admit, that despite following the technological novelties related to mirrorless cameras quite closely, a few interesting facts escaped me, causing me some surprise and even confusion. So, as with any other equipment, it's worth knowing as many facts as possible to be prepared and avoid some surprises.

Nikon Z Series Mirrorless

Starting from the beginning - the brand I chose some time ago is Nikon, and the factor that ultimately decided on this choice (leaving aside mainly Canon and Sony) was the ergonomics of Nikon SLRs, which both in terms of physical design and arrangement of buttons/function knobs, as well as ergonomics of the in-camera menu, in my opinion had no equal. Of course, there are other technical parameters which are far more critical when choosing equipment, but at that time the other key parameters of each manufacturer were so similar, that I had to make my choice based on at least one outstanding factor. Nikon was also the first company to release a DSLR and in getting to know the brand I went through the D200, D700 and D810 successively in my practice.

I still own the D810 DSLR and use it in my professional business. I consider it to be one of the best models from Nikon and beyond (other than the D850 and naturally the D4 line). However, time moves on and with the very rapid development of the mirrorless market, the DSLR segment has naturally slowed down, also having virtually the end of further development on its horizon. In addition, the need for filmmaking began to appear in my work, which accelerated my decision to purchase new equipment - the choice fell on Nikon Z7 II. I decided to stay with the Nikon brand, because of my commitment to its philosophy, and also to avoid all the confusion that would be associated with changing brands and the large additional costs (including the need to change the lenses and associated equipment such as flash units and radio transmitters). This comment has to do with the fact that Nikon in its mirrorless cameras slightly lagged behind its main rivals - Canon and Sony, primarily in terms of the key and expected by me solution - effective eye tracking (Eye AF). However, the appearance of dual-processor models Z6 II / Z7 II created the announcement of a major advance in this direction and helped in my decision, especially in light of the upcoming sensational Z9 model, part of whose eye tracking algorithm in real mode, was to be made available in lower models as a firmware update.

Nikon D810 and Z7 II camera comparison - rear view with function buttons and screen

I realize that every photographer may have experiences different from mine - I will be very happy to hear them as comments. Also, the validity of some of the information presented here may change over time, along with the emergence of new models of equipment and new versions of firmware made available by the manufacturers.

After this substantial introduction, now about specifics.

2. Auto Focus - the effectiveness of the AF mechanism

One of my primary problems with my DSLR is the front focus and back focus phenomenon, resulting in a certain volume of out-of-focus photos depending on the lenses used (fixed focal length/zooms) and the focal length values chosen, I was getting some number of photos being unsharp. In my case, this is quite a nuisance when a large volume of captured images are out of focus. Professional DSLR cameras allow you to calibrate the lenses by entering correction values for each lens. Also some lens brands, like Sigma, allow you to calibrate the lens itself based on, for example, the 3 most commonly used focal length ranges. These solutions are of course very useful, but at the same time troublesome. Calibration of Sigma lenses requires use of appropriate attachment to which the lens is attached and connected to computer via USB, and then dedicated software sets parameters for points confirmed earlier by focus tests, using e.g. focus cards. It is also cumbersome to have to verify and possibly recalibrate on a regular basis every so often. Another option is sending the DSLR and the lens to the Sigma service to 'pair' the two devices together, because most often the calibration concerns a particular DSLR camera - putting a calibrated Sigma lens on another body does not guarantee a good result. The whole thing can look quite breakneck.

Nikon D810 DSLR menu - settings for fine-tune AF

In my particular case, the back-focus/front-focus phenomena made the lenses I bought - Nikkor AF-S 85mm 1.4G and Sigma Art 35mm 1.4 - of great quality, almost reference, practically useless with my D810 DSLR, because of very high instability of the AF system and a large percentage of blurred photos. The interesting thing is, that my photographer friend had the opposite situation - his D810 worked great with fixed focus lenses in this category, while the unstable focus appeared with zoom lenses, which I have no problems with.

What is the reason for this situation? The reason is the method of focusing used in DSLRs - that is, the so-called phase detection: the camera focuses with sensors outside the main sensor of the camera, which are located under the chamber of the mirror; the light passes through the lower, semi-permeable part of the main mirror, then is reflected by the auxiliary mirror, from where it is directed downwards to the AF sensors. You could say that this is the disadvantage or disadvantage of this method of sharpening, however this method also has an advantage, about which I will write a little below.

And how is it in mirrorless cameras? Here, due to the lack of a mirror, a different autofocusing technique is used - based on the contrast of the image available directly on the sensor. In simple terms, focusing on this principle is done by software, not hardware - the camera simply measures the level of contrast in a place selected by the photographer, and by moving the lens back and forth, selects the moment when the contrast, in the selected section, is the highest. What causes this? - The result is, that in the case of mirrorless cameras the front-focus/back-focus problem ceases to exist and the lenses do not need to be calibrated. In practice, however, camera manufacturers add a calibration function in the menu which can still be used in some special cases.

To sum up: phase detection in DSLRs is less accurate than focusing based on contrast measurement. Nota bene, the latter method of measurement is also used in DSLR cameras in Live View (LV) mode - but this is a separate topic - the pros and cons of shooting with a viewfinder and LV mode (not covered in this article).

3. Auto-focus speed - two solutions for AF

Nikon Z Series Mirrorless Camera - AF Assist Green Light

Green light AF assist beam on Nikon Z-series mirrorless camera

I mentioned above, that the phase detection focus metering system in DSLR cameras has an advantage in addition to its disadvantage. Well, this method of automatic focus metering is definitely faster than the contrast metering method. This means, that a mirrorless camera generally takes longer to focus compared to a DSLR. However, this is dependent on the light level of the scene - the brighter it is, the less noticeable the difference in speed. Similarly, this speed also depends on the quality of the sensor - the better the sensor, the more sensitive, the better it handles low light, the difference in speed compared to a DSLR will be less noticeable.

In general, in very low light, mirrorless cameras are worse at focusing quickly. You can, of course, help in such situations with additional lighting (the camera's LED light beam activated in low light), but in the case of DSLRs this is associated with another inconvenience - the color of such light, in contrast to the white light in DSLRs, is intensely green, which when photographing people can be very tiring and absorbing their attention, affecting very negatively e.g. reportage photo shoots. And why is this color (unfortunately) green and not white as before in DSLR cameras? Because the focus sensors on the sensor are located under the green/blue filters, causing the green light to support the AF function more effectively.

4. Battery life and number of photos per battery

The thing, that bothered me all the time, while reading the manuals of various manufacturers of mirrorless cameras, studying posts and comments on various discussion groups and blogs, getting to know the opinions on websites describing the tests of equipment - is the working time of the camera on a single battery, i.e. the maximum number of shots. DSLR and mirrorless have different power requirements. In a DSLR, power is needed at the moment of focusing, measuring the light level and using the rear screen (viewing photos, using the menu or the LV mode) and of course at the moment of taking the picture. The image in the viewfinder is always visible, even when the DSLR is turned off. A mirrorless camera has a much higher demand for power - here the viewfinder, like the rear screen, is also a kind of screen and requires power. So we can only see the image when one of the screens is on, which makes the power consumption potentially much higher compared to a DSLR. This was one of the things, that most strongly triggered my doubt as to whether it was a good time to start with a mirrorless. According to the manufacturer's information, as well as most of the first users, one battery allowed to take 350-500 pictures, and this number also depends a bit on the size of the camera's sensor (the bigger the sensor, the more information needs to be read from it and saved on an external memory card). I was somewhat optimistic about the small number of opinions that, with the right approach to using a mirrorless camera (including setting display parameters and some good display usage practice), you can comfortably achieve up to 1500 photos on a single battery. My first tests definitely confirmed this. On my D810 DSLR (36Mpx sensor) I could easily reach the numbers of 1500-1700 pictures on a single battery, so 3 batteries were enough to work on e.g. 10 hour reportage. The big and very positive surprise for me was that my Nikon Z7 II (45Mpx) allows you to take about 1500 pictures on one battery, and the other batteries I bought are only a form of backup.

5. The Matrix - Solutions in DSLR and Mirrorless

Nikon Z-series Mirrorless Camera - view of the sensor with lens removed

The sensor in a mirrorless camera as seen when the lens is removed

What is quite important in case of interchangeable lens cameras is the fact, that every time you change the lens a certain number of dust particles, pollen or other factors get inside the camera. Some of them get directly to the sensor causing unwanted specks on the registered image (and the bigger the aperture is, the sharper the specks are). It is of course an unwanted element, causing additional work in digital processing of the photos and laborious removal of its impurities. The more speckles, the more processing work and, similarly, the necessity of more frequent visits to camera service center in order to clean the matrix (you can clean it yourself, of course, but that's another topic).

In case of a DSLR, the matrix is covered by the mirror most of the time and it is the same when you change lenses. So the matrix is covered at that time causing the possible contaminants not to get on its surface, and those that got inside before the matrix can get on it only at the moment of taking the picture.

In a mirrorless camera the situation is different - there is no mirror here, so nothing covers and protects the matrix - when you change the lens it is exposed directly to external factors and the chance of getting contamination on the surface of the matrix is much greater. This chance is also increased by the fact that in a mirrorless camera the sensor is more protruding towards the lens opening (the body is shallower because there is no mirror), so it is closer to potentially adverse conditions. So it is definitely a disadvantage in this context and requires more care e.g. when changing lenses. Manufacturers are beginning to introduce solutions based on mounting in the body additional internal sensor covers (a kind of curtain), which are to protect it when removing the lens, but in most cases they are currently quite ineffective (slow working). The only exception is the flagship Nikon Z9 mirrorless camera, which allows you to automatically shield the sensor in just a fraction of a second when removing the lens.

6. 24Mpx or 45Mpx sensor size (same physical size)

I mentioned above, the aspect of the sensor size, which affects various issues, however there is no special distinction here in the case of DSLRs or mirrorless, apart from the possible issue of slightly higher power consumption with its larger size in mirrorless. The choice of the matrix size depends mainly on your needs - what kind of photography you take and what is its purpose. Smaller sensor means smaller costs - cheaper body, smaller capacity of memory cards, faster transfer from cards, smaller volumes of storage media for archiving photos, smaller power requirements for processing photos by dedicated software. Smaller sensor also means a chance for sharper video images.

However, I chose the large 45Mpx sensor, which is more dictated by my nature of work as a photographer. Larger sensor allows me to crop photos, which is a kind of lossless zoom (of course with a certain size of the resulting photo). Bigger sensor means definitely better quality of photos/posters printed in large formats. Additionally, the larger the sensor the potentially higher tonality of the captured image. On the other hand, a smaller sensor means a larger size of photosensitive elements, that can capture more light, which results in lower noise level and better image quality.

7. Speedlights and Transmitters - (no) Focus Assist

V1 flash and red AF assist light

This is one of those features, that escaped me while studying information about mirrorless cameras. I was used to it and used this feature a lot - most flashes and remote flash control transmitters have an additional option to activate AF assist light and emit a red light beam to assist focusing in lower light conditions. My first attempts to set this up on my mirrorless Z7 II ended in failure and a slight panic that my new gear was defective. What turned out after a lengthy internet search? - In the mirrorless Z7 II the focus sensors are located under the green/blue filters, which makes the red light invisible to them, therefore the body does not send any signal to the flash or the transmitter to activate the AF assistant and the red light will not appear in any case.

8. A few words about lenses

Nikon Z-series mirrorless camera and FTZ adapter for F-mount lenses

Nikon FTZ adapter for F-mount lenses

Mirrorless differs from the SLR in physical size - the basic and natural reason is the lack of the mirror, which makes the body is simply thinner and the distance between the matrix and the plane of the lens mounting hole is smaller. For this reason, new lines of lenses are dedicated for mirrorless cameras, so you can not directly mount SLR lenses on such a body. However, there are no problems with using existing SLR lenses, because the manufacturers offer a special type of adapters - rings that increase the distance between the matrix and the mounted lens, which also transfer all the electronics between these devices.

From my own experience I can say that in the case of Nikon Z7 II it works great and I did not encounter the slightest problem - the speed of sharpening and the quality of photos is at a constant level compared to the SLR.

9. Ergonomics

Nikon Z-series mirrorless camera rear view with function buttons and screen

In the previous point I mentioned that a mirrorless is smaller in size compared to DSLR, there is no mirror, so the whole structure is flatter and lighter, but also both main dimensions - especially the height of the body has also decreased. The whole thing is lighter and smaller, so for example it is a bit easier to transport the equipment. The smaller design, however, has a considerable, unfortunately unfavorable effect on the ergonomics of the camera. Nikon Z7 II compared with the D810 is definitely less suitable for the hand, the operating buttons here are placed closer to each other, and in addition, due to the smaller size of the whole, the manufacturer focused on providing the possibility of operating the buttons with only one hand (the left one holds the camera, the right operates the functions). So almost all the buttons and knobs have been moved to the right side, which unfortunately is not convenient due to the size. Of course, you can get used to everything, although there's no denying, that in terms of ergonomics SLR and mirrorless are two completely different devices.

10. Viewfinder - Natural mode view

The viewfinder on a DSLR always shows a natural image/scene - among other things, it shows the brightness level of the scene as it is in the environment - it is a natural view. This has an obvious advantage, because through the viewfinder you can see the actual lighting of the scene. On the other hand, if we want to intentionally underexpose the picture - e.g. to bring out only the outlines of people on a bright background, or the other way round - to overexpose - bringing out details in dark places - this kind of pictures usually have to be taken by trial and error, correcting the exposure settings and checking the result after the picture is taken.

In mirrorless the situation is different - in the main mode viewfinder screen shows the current scene taking into account the exposure settings - if you want to underexpose the scene just adjust the exposure until the viewfinder shows the expected state - the photo will look exactly like the image seen in the viewfinder. Mirrorless cameras have an additional mode which may be selected, that allows you to view the image in the viewfinder in the same mode as in SLRs - so you can easily use this option if necessary, and this is usually the case when shooting with flash, when it is important to preview the current, natural lighting of the scene.

11. A longer life span for mirrorless cameras?

A mirrorless camera, by its nature, does not have a mirror, so there are no mechanisms in the body of such a camera, that operate the movement of the mirror, which are required in a DSLR. It is known, that mechanical components are the parts that wear out over time causing an increased risk of failure. Therefore, theoretically, you can expect a longer life of the mirrorless and a higher mileage. In practice manufacturers are quite careful and e.g. in the case of the D810 DSLR and the Z7 II mirrorless they declare analogous failure-free operation times, i.e. the maximum actuations - the guaranteed number of photos without failure.

12. Is a mirrorless just about quiet operation?

Rolling-shutter effect on an old photograph - a typical example of how the electronic shutter of a mirrorless camera works when shooting fast-moving subjects

Rolling-shutter effect well known from old photographs

SLRs have two main shutter modes, referred to as mechanical and electronic shutter. Generally, these types of cameras are much quieter than SLRs already in the main mechanical shutter mode (the lack of mirror mechanisms also does its job). However, the electronic shutter mode provides a complete absence of sound, allowing you to freely take pictures in even the most demanding situations, such as during a concert with very quiet music. The electronic shutter mode uses practically no mechanism that could wear out.

However, the electronic mode has its drawbacks and limitations - when photographing fast-moving objects the recorded image may contain geometric distortions of such objects (the so-called rolling-shutter effect), which is caused by the fact that the data is read out from the sensor linearly (successively line by line). Each line is exposed at a time set by the user (e.g. 1/16000s), but the data from the whole matrix take a little longer to accumulate. As a result, with very fast moving objects, these differences may cause characteristic distortions, showing the photographed object unnaturally twisted.

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