What do I expect from a good camera?

Over the course of three years of regular work with the camera, you slowly realize what you need or what is important to you. I work in many different areas of photography. Wildlife photography is essentially different from landscape photography or even night photography; in macro photography there are numerous subdivisions, all of which have different requirements. And this year (2022) I even got to work as a wedding photographer for the first time. From all these practical experiences, the following combination is best for me (may differ for everyone):

Continuous shooting speed

When I started my hobby, I would never have imagined how complex this point could be. Continuous shooting, i.e. the number of images per second, is a decisive factor in many areas of photography. When observing animals, you need high frame rates to capture various fast situations. For example, for kingfishers. But this also applies to insects. Whether the butterfly or the dragonfly. Close-ups produce extremely high relative speeds that need to be captured. My optimum is around 15 frames per second. Personally, I find that anything above that produces too many images that are very similar. With lower continuous shooting speeds, you tend to miss exciting subjects.
However, many images per second are not only an advantage for event or animal photography. Landscape photography can also benefit. When working with exposure series and panoramas, things sometimes have to happen quickly. Weather and lighting conditions can change rapidly. What's more, in some cases the tripod can even be dispensed with. Provided, of course, that you shoot with fast shutter speeds.

And a note on continuous shooting speeds far from 20 photos/second: videos start at 24 photos/second. If you think you need to buy cameras with higher continuous shooting speeds, you can simply record a video. 30 or more FPS is usually no problem. You can also isolate individual frames later. A big problem with photography is sifting through all the individual images and working with them. This brings the computer to its knees very quickly.

Buffer or intermediate storage

As I had already discovered with the D3100 and the D7500 or even the D5600, the internal memory of a camera sometimes fills up. Emptying it into the external memory card can take a while. This means that photography is slow. These are often the situations in which something cool is constantly happening. There are two points to consider at this point. Firstly, the transfer rate and secondly, the camera's internal storage capacity. When using CF-Express or XQD cards and the newer professional mirrorless cameras, the buffer memory can sometimes no longer run full, as the data can be written to the card quickly enough. If this is not the case, I would always aim for a buffer capacity of 50 images. However, this only applies to those who already know how to use the shutter button. If you like continuous shooting, you should plan for at least double that.

Noise behavior (ISO)

For me, a very decisive criterion for a purchase is always the image noise at high ISO values. The ISO stands for the amplification factor in the camera. If there is little light on the pixel, the electronic amplification must be all the more effective. In physics, there is a technical term that is often used in this context, the signal-to-noise ratio. In other words, the signal-to-noise ratio. The basic concept is that every sensor, whether it is the chip in the camera or a microphone, has a background noise. If we want to receive a signal that is very weak, we have to amplify it. However, this also amplifies the noise. This can often be seen in the form of artifacts on the image. Full-frame cameras can handle an ISO of 1000 without any major problems. Especially in post-processing, a lot of noise can be removed, masked or corrected with AI support. However, the resolution plays a decisive role here. A sensor with 20 megapixels and a sensor with 40 megapixels with the same sensor size differ massively in their noise behavior. While in the first case the area of the pixels is quite large, they can collect a lot of light/data/information. A smaller pixel does not get quite as much. Its signal-to-noise ratio is therefore worse. However, cameras with many megapixels can resolve much more detail. You just need a lot of light.
So the question is: what do I want to photograph and how much noise can I live with? At this point, we must also not forget what I want to use my photos for. For small prints up to A3, these values are almost completely irrelevant. Especially since no one stands in front of a picture with a magnifying glass, but always maintains a certain impression distance. The really big advantage of many megapixels is simply the variability in cropping the motif. Lemicoles, for example, are quite shy and need large safety distances. They therefore appear very small in the image.

Shutter speed

Another factor in the evaluation of cameras is the shutter speed. Some high-end camera manufacturers have now reached 1/32,000 s. There are a few crucial questions to be answered at this point. In the areas where I photograph, there have only been two animals that would have needed such short shutter speeds. Bumblebees and dragonflies! But only to freeze their flapping wings in flight. The big problem with extremely fast shutter speeds is the amount of light that hits the sensor. You could also say the little bit that remains. That is extremely little. Which brings us back to the ISO, which is then quite high. In my opinion, 1/8000 seconds is more than sufficient for amateurs and professionals. For landscape photographers or night photography, this minimum possible value is also largely irrelevant.

Battery life

The difference between DSLR and DSLM is around 3 to 1. Mirrorless cameras draw significantly more power due to the electronic viewfinder. It is therefore advisable to have several batteries with you anyway. The Z6II usually manages around 500 pictures. A D750 is more likely to take 1200 pictures on one battery charge.
There is a major shortcoming with mirrorless cameras for video recordings or time lapses. Here, the camera should support external power banks. For sesions lasting several hours, 30,000 mAh is usually sufficient. However, the external battery must now also be capable of PD more often. For longer stays over night or days, a small power station is recommended. Especially if you want to work with two cameras or a laptop at the same time.

Resolution

As I wrote in advance, higher-pixel sensors like the Z9 have a poorer signal-to-noise ratio, but deliver more detail. One point that I have become increasingly aware of recently is the file size of images. Although 45 megapixels give room for cropping, they put a strain on the hardware. Especially when working with high continuous shooting speeds, overlaying panoramas or bracketing. In terms of memory size, 20-24 MP sensors with a RAW take up around 25 MB. At 45 MP, the storage space roughly doubles. Only around 200 images fit on 1 GB. In fact, when choosing a camera, you should be careful in which direction you go. A Z9 may make sense for shy animals and large format prints. For landscape pictures or small prints, however, significantly fewer pixels are sufficient. At this point, I would like to point out once again that the current technology trend with more and more megapixels is not as sensible as it seems. Neither for cameras nor for cell phones.
As a final important note, I would like to point out the lenses used. The optics used refract, bend, absorb and reflect light. What hits the front lens is therefore greatly altered. The resolution can suffer as a result. Older lenses, or cheap variants that do not have the necessary glass or nano-coatings, are not able to handle 45 MP at all. In other words, there is no point in having a high-end camera in your pocket if the lens does not have the necessary quality.