Any camera that allows manual control of focus and manual control of exposure should be usable for astrophotography. But both of these are requirements (not just "nice to have").
There is a strong advantage to having a camera with a larger (physical dimensions) sensor (more on that in a bit).
The focal length of the lens need not be particularly high (more on that in a bit.)
You will also need a tripod. If you don't have a tripod, then you might get away with propping the camera on something solid. The important bit is that you cannot hand-hold one of these shots. The shutter will need to be open for ... a long enough amount of time that hand-holding is not an option (you'll get nothing but blurry shots caused by camera movement.)
Most objects in the night sky are just too faint for any auto-exposure systems to work (with the exception of the Moon).
When you focus manually, select a bright star and focus with an effort to try to get that star to be the smallest possible point. You can use a live-view mode on a camera. Many cameras let you zoom in on a small area in the live-view mode to refine focus (this doesn't change the shot ... you'll still get the whole image. It just lets you check focus in a specific area by acting as a kind of digital magnifying glass.)
There is a gadget called a Bahtinov Mask and these can help simplify the focus task. Remember... pick a bright star for focus, not the object you intend to photograph. If anything in space is focused, then everything in space is focused. You can focus on the star, then re-frame the camera on the comet and you will still get a properly focused shot. The Bahtinov mask isn't necessary... it's just a "nice to have" focus aid.
Also, automatic exposure systems make assumptions about scene brightness. They are designed for taking photographs in adequate light -- not nighttime. Even the "nighttime" modes that some cameras have make assumptions that there's a nicely lit foreground subject.
To come up with this exposure there are a few guidelines.
You'll generally use the widest possible aperture (lowest "F-Stop" value or "Av" value) that your camera will allow. This allows the maximum amount of light through the lens. Remember it's dark out and these are faint objects... you need every possible photon you can get.
But there is a trade-off... which is that some lenses exhibit some optical aberrations if they shoot "wide open". You can sometimes really improve the quality by just slightly reducing the aperture size (meaning shoot at an F-stop value just slightly higher than whatever "wide open" is on your lens. e.g. if you have an f/2.8 lens, maybe shoot at f/3.5 or f/4.)
Shutter Speed (exposure time)
This one is a bit tricky because the Earth is spinning. Specifically the Earth spins at a rate of about 15 seconds of arc per second of time. (15 arc-seconds per second.) If the exposure is too long, the things that should be pin-point (stars) will be elongated or blurred due to the motion of the Earth.
There is a general guideline called the "600 Rule" (more on this in a moment) but some photographers think the number is a bit too generous so they use a more conservative number like "500". Some photographers use even lower values.
This rule was created for use on 35mm film cameras. 35mm was the width of the film ... including the areas where there were sprocket holes in the edges of the film used to help wind it. The exposed area is not actually 35mm in any dimension. The exposed area is 36mm wide by 24mm tall (or a diagonal measure of just over 43mm). When a digital camera has a sensor which is the same size as this very common film standard, that camera is referred to as having a "full frame" sensor. (A strange name considering there are sensors both smaller and larger. So don't let the name confuse you into thinking this is the largest possible sensor size.)
Full-frame digital cameras tend to be expensive (certainly more than $1000 USD even for an inexpensive full frame camera). Most consumer cameras use smaller sensor sizes. It is actually important to know what size sensor you have to work out the exposure duration. Don't ignore this information or you will struggle to get good results.
Very commonly, removable lens cameras use APS-C size sensors. These sensors are referred to as having a 1.5 or 1.6 "crop factor". What this really means is you take the dimensions of a full-frame sensor (36x24 or 43mm diagonal) and then DIVIDE those values by 1.5 or 1.6... you'll get the dimensions of that camera's sensor. But it turns out the reason you wanted to know the sensor size was to determine the cameras's crop-factor. So if you know the crop-factor you don't actually need to know the sensor dimensions.
For purposes of example, let's assume you have a DSLR type camera with an APS-C camera. If it's a Canon it has a 1.6x crop factor. If it's a Nikon or Sony then it has a 1.5x crop factor. There are other cameras such as 4/3 format cameras that have even smaller sensors. You'll find that having the largest possible sensor you can afford works to your favor for this type of photography.
If we have an actual full-frame camera, you divide 600 ... by the focal length of your lens. The result you get is the number of seconds that you can expose... and still have reasonably pin-point stars. If you really get in and inspect those stars very closely you might notice they aren't perfectly pinpoint from a distance it wont be noticeable. Some photographers use a smaller number than 600 to be a bit more conservative.
If you have a full-frame camera using a 200mm lens, then 600 ÷ 200 = 3. This means you can take a 3 second exposure and should not have noticeable elongation of the stars. If you used a 100mm focal length lens, then you could expose for 6 seconds because 600 ÷ 100 = 6.
Simple enough so far?
But now apply the crop-factor. If you have an APS-C camera (and I'll just use the 1.5x crop factor because the math is easier) ... you have to divide 600 by the crop factor. 600 ÷ 1.5 = 400. NOW divide that by the focal length of your lens.
E.g. with a 200mm lens, then 400 ÷ 200 = 2 -- just a 2 second exposure. With a 100mm lens you can expose for 4 seconds.
There is something else working in your favor. I mentioned earlier that the Earth spins at an angular rate of 15 arc-seconds per second. But this is the speed of a star moving at declination 0°.
Declination, in astronomy, is like latitude on Earth ... except in the sky. If a star appears to be located directly above Earth's north pole, that star has a declination of +90°. If a star is directly above Earth's south pole, that star has a declination of -90°. If a star appears to be located somewhere above Earth's equator (if you were on the Equator and... at some point during the night that star would pass directly above your head at the Zenith) then that star has a declination of 0°.
But a star located direction above Earth's north pole ... doesn't move ... at all (from our point of view --- at least not fast enough to be noticed in a single human lifetime). Polaris (the North Star) isn't perfectly at +90°. It's more like 89°20' (it's roughly 2/3rds of a degree away from the true celestial pole... but it's within a degree so we call it the "North Star").
You can use a bit of math ... and it's pretty easy but you will need a calculator with the trig functions ... specifically the Sin & Cos (Sine & Cosine) functions.
If you multiply the rate of Earth's spin by the cosine of the object's declination, you get the apparent rate of movement for that particular object. This is where it gets interesting.
Comet C/2020 F3 NEOWISE currently has a declination of about +47°. The cosine of 47° is .68. This means that instead of 15 arc-seconds per second... it appears to be rotating at 15 x .68 = 10.2 arc-seconds per second.
This reduction in speed (by nearly 1/3rd) means we can increase the exposure duration proportionally. This means if we used the example where we could only expose for 4 seconds... we could push that up to about 6 seconds and be ok.
Lenses (Angle of View and Focal Lengths)
The comet currently has a tail at least 5° long. I've heard at least one report claiming it is more like 7° long.
This means you want an "angle of view" that can capture not only the head of the comet, but the tail as well. The "angle of view" calculation is a function of the physical dimensions of the shutter and the focal length of the lens. So you want a solution that can capture the entire tail of the comet.
If you use a field-of-view calculator -- like the one on this page -- you can work out the angular field of view for any camera & lens combination as long as you know the crop-factor of the camera sensor and the true focal length of the lens.
Using this, I find an APS-C sensor camera with a 200mm lens would just barely fit the comet and tail into the frame. This assumes you want nothing else in the frame (no skyline, etc.). I would certainly not recommend any lens with a longer focal length.
A focal length of around 100mm would likely be better ... and you could even get away with a little less if you are hoping to include some sky-line in the photo. As the days go by, the comet will start appearing slightly higher in the sky. But this will vary based on your latitude on Earth. I'm at +42°N Latitude and at 10pm for me (July 19) the comet is 22° above the horizon. At 11pm it is only 14° above the horizon. From my location the comet is currently circumpolar (meaning it will not set below the horizon). You can see where I'm going with this... if you have a comet with a 7° long tail (pointed upward) and a horizon line that is 22° below the head of the comet ... now you need an angle of view that can cover more than 30°. We're starting to get to where even a 50mm lens is too tight and something more around 28mm would be better.
The point is ... big long lenses are not necessarily the best choice depending on what you want to include in the frame.
What to buy
This gets a bit tricky. I usually like to recommend "qualities" that a product should have any not a specific brand or model. Any any recommendation for a brand can quickly turn into a Coke vs. Pepsi and Ford vs. Chevy debate over who has the best brand. It's really not about the brand... it's about having the right feature set.
But I sense you were really hoping for a specific camera recommendation (brand and model).
First, consider that if you don't plant to get into astrophotography as a regular practice, but want to capture this comet while you can... then renting is certainly an option that you should consider.
If you really want to buy a camera then remember the qualities that are helpful:
- Largest possible sensor size you can afford. This is because the larger the sensor, the longer you can expose when you apply the "600 Rule". This helps you collect more light without having to apply gain (aka increasing the ISO value ... which will result in more obvious "noise" in the photo).
- Manual focus and manual exposure control are absolutely required. Don't consider anything if it doesn't offer you this control.
- Removable lenses ... so you can select the lens most appropriate to the task. Lenses with very low focal ratios are helpful because they let you collect more light. Unfortunately these same lenses tend to be noticeably more expensive.
With respect to brand and model. Canon tends to be favored for astrophotography. This is because in astrophotography -- especially astrophotography of deep-sky objects via telescopes -- the camera is typically computer controlled. Canon made their EOS SDK available at no-cost to developers and this SDK can control virtually any EOS camera regardless of model or price tag. This is not true of the other brands. As a result, there is a considerable choice of astrophotography image-acquisition software available that supports Canon EOS cameras (far more than for any other brand.)
Also, keep in mind that in astrophotography, everything is manual. We don't use auto-focus. We don't use the in camera metering system (and certainly don't use auto-exposure). The exposures tend to be long (many seconds) so having a camera with an extremely rapid-fire shutter has no value. Given these facts... a fairly basic model fits the needs quite nicely. These tend to be the least-expensive models.
If this was not a request for a camera for astrophotography, I would not necessarily recommend Canon. I make the exception for astrophotography because with years of experience, I know far too many people who bought something else and regretted it because of the lack of software support and some missing features that are especially useful for astrophotography.