Having now used this camera for bird photography over some days I can offer a few more thoughts which may be of help to anyone who is contemplating getting it. This is also, in part, a comment on some of the common themes that can be found from the various blogerati on YouTube and elsewhere, because I expect most people will turn to their favourite YouTuber or review site in the first instance.
It's not the R5 (or the R3)...
I find a fair amount of commentary essentially amounts to a commentary about how the R7 compares with its bigger full frame siblings. Fair enough, but inevitably this ends up emphasising the things that it does less well. If you want the features of an R5 (or R3) and have a loose $5.5 K (or $8.5K) then get those cameras. This camera only costs around $2.2K, yet includes many of the features of the full frame models. Inevitably this will lead to some negative comparisons because there are going to be things at the margins you can do with the more advanced cameras that you can't do with this (or which are more difficult to do).
The Buffer
The other day I met a complete stranger who was out photographing birds locally. He glanced down and noted the R7 moniker, and immediately asked 'How are you finding The Buffer...'. The Buffer - and its limitations - seems to have captured everyone's attention and is normally high on the list of vloggers' 'things I don't like' lists.
According to DPReview the camera can shoot about 65 frames of cRAW files at the maximum rate of 30 fps (electronic) and about 100 files at the maximum mechanical rate of 15 fps before the buffer is full. With the fastest electronic shutter setting this is some 2 seconds of shots before the buffer is full.
I guess it is what it is, so buyers just have to be realistic. If you are someone who likes to hold down the shutter button for longish periods and take hundreds of shots at a time, then you are going to have problems. If you are someone who shoots in short bursts of up to half a dozen shots at a time, with breaks in between, you are not likely to run into a lot of problems if you use a fast SD card.
By the way, there is a thing called Raw Burst Mode which, when set, starts to record raw images when the shutter is half pressed (using the electronic shutter). This allows about half a second's worth of images to be stored from immediately before you fully press the shutter button (ie about 15 images at the fastest electronic shutter speed). The idea is that this can help ensure you don't miss key action shots due to slow reaction times. These images are all wrapped in one single file from which individual raw files can subsequently be extracted using Canon's DPP software.
The sensor
I am waiting for DxO to be able decode the files, but the sensor has very similar specifications to that in the 90D. Obviously a high megapixel APSC sensor will show noise, but the results I am getting clean up very nicely in my trial copy of Topaz Denoise, and show good colour and sharpness. I understand its a new sensor, according to Canon, but it is still just 'regular' CMOS, not back illuminated or stacked. This affects the read-out speed, giving problems with rolling shutter (see below) and possibly with speed of tracking in extreme situations. The Photons to Photos web site found that the dynamic range of the sensor is slightly better than the 90D.
The sensor is stabilised.
Rolling shutter
Rolling shutter (the distortions that occur when shooting fast movement with the electronic shutter) is definitely an issue (including in video, from what I have seen online). It seems generally fine in situations where the bird is relatively static, moving slowly etc. But fast lateral movement will result in distortion. This is most evident with straight objects in the background eg I tried panning to photograph some flying gulls with the local communications tower in the background and while the bird did not seem to be obviously affected, the tower was canted over quite noticeably in the photo. You can see lots of examples of this in various online commentary (including the traditional distorted drone or helicopter rotors). So for birds in flight, you will probably need to use the mechanical shutter - electronic first curtain shutter (EFCS) seemed to fix the problem.
This is an obvious issue with the camera's marketing. The 30fps is touted as a headline feature (with the obvious inference that this will let you capture every nuance of the action), but the rolling shutter will make it difficult to use for any fast action that moves across the screen. I can see it possibly working for some subjects (eg a bird moving across the blue sky where there is no background to distort, or a bird or animal coming towards you). However the 15 fps EFCS is probably a more realistic measure of its BIF capabilities.
Autofocus
This is obviously one of the, if not the headline feature of the camera. According to reviews and what I can see in the manuals, it is identical or nearly identical in terms of features/menus/settings to the R3 but with fewer focus points (which is not surprising given it is a smaller sensor). It uses the latest iteration of the Dual Pixel phase detect system.
The camera has traditional Canon settings for use of autofocus points, including Spot, One Point, the 5-spot setting (called Expand AF), the 9 spot setting (called Expand AF Around), and the wide setting using the entire sensor (called Whole Area AF). It also has three pre-set zone systems using differently-sized boxes in the viewfinder (called Flexible Zone AF). The size of these zones is user-adjustable.
Out of the box the camera is set with subject tracking On, eye tracking On, and the Whole Area setting. With eye tracking set to Animal, it works remarkably well in this 'auto' setting, finding and tracking birds and their eyes. Like any AI-based system it can get confused, and can struggle with subjects which are very small in the frame or not clearly distinguished from the background, but it does a remarkably good job.
At a deeper level it is possible to set all sorts of variables, which can become bewildering (and is not always intuitive - at least to me). Beginners may struggle to get much beyond the default auto setting.
I think a mistake that photographers will easily make with this camera is to assume that bird eye tracking is a one-size fits all proposition, and become lazy about the basics. There are still plenty of situations where traditional non-tracking servo autofocus, and one-shot autofocus will be appropriate or even preferable. So in my opinion it is best to set this camera up to be able to quickly switch tracking On or Off.
Somewhat counterintuitively, it seems that in order to do this you have to switch Subject Tracking Off in the menu (so the camera starts up in traditional non-tracking autofocus mode). You can then set up buttons to do things like toggle Subject Tracking On or Off, or toggle Eye Tracking on or off. I won't go into detail here but suffice to say it pays to study the system carefully and experiment with different settings, whether you are a back-button focuser or a front-button focuser, as the interaction between options can become confusing.
The other thing it took me a while to work through is the way it uses focusing points to start tracking. Tracking can work with any of the autofocus areas, from Spot all the way to Whole Area. However, the autofocus area you select will determine where that tracking starts. Objects will only be tracked if they are located within, or immediately adjacent to the autofocus area you select. Subjects outside the area will be ignored. (Obviously, this limitation doesn't apply to Whole Area focus mode.) However, once tracking has commenced, it can follow the subject throughout the scene, for as long as the focus button is pressed, even if the subject moves outside the initial focus area.
Please let me know if you have any questions.
