One of the important differences between Interchange Lens Cameras (ILC) and bridge cameras is the "shooting envelope". That's the range of images the camera can capture.
You want to get a camera that has a large enough shooting envelope to capture the images you want. You don't need to worry about the ability to capture other types of images.
As a general rule you get the same image with the same subject, aperture diameter, and shutter speed. This is independent of sensor size. By "same image", I mean same depth of field, motion blur and overall image noise.
The advantage of larger sensor cameras is that the generally allow you the option of using larger aperture diameters, which yield shallower depth of field and the associated better low light performance. While some photographers love the look of very shallow depth of field, it isn't for everyone. If you don't need it, then you don't need a camera that provides it.
An advantage of an ILC is that you can change lenses. If you decide you want a wide angle lens, a macro lens for very close focusing, a fisheye lens, a probe lens, or other specialty lens, then you can get one. If you are not interested in that sort of thing, then you don't need an ILC.
An advantage of an all-on-one camera is that it is convenient, light weight, and tends to be more affordable. If you can find one that covers the shooting envelope you are interested in, then they can be an excellent option.
Consider the RX10-IV. It's roughly a 3X crop body. The actual focal range of the lens is somewhere around 8mm to 200mm, and it has a relative aperture range of f/2 to f/4.4. This camera covers a reasonable shooting range, and can be a good choice for many.
Aperture diameter is the focal length divided by the f/stop. At the wide end the RX10-IV lens has a 4mm aperture diameter (8mm/4). At the telephoto end it has a 45mm aperture diameter (200mm/4.4).
It's a crop body, and that lens offers the same angle of view as you would get with a 600mm lens on a full frame. A 45mm aperture diameter on a 600mm lens would be about f/13.2. Therefore, we know that the 200mm f/4.4 lens on the RX10-IV is going to give us the same results as a 600mm f/13.2 lens on a full frame.
Very-Very Misleading ...
It is a f/2.4 to f/4
Sorry. Let me correct my statement to "200mm at f/4 on a 3X crop body will give us the same results as 600mm f/12 on a full frame."
Some people are under the impression that with a full frame body, you would need to spend $12,000 on a 600mm f/4 lens in order to match the results of the RX10-IV. That's not the case.
If I have a (FF) dSLR and I shoot a shot (aka of a bird @ 600mm) and I want to shoot ISO-100 (for lowest noise), and 1/2000s (to stop/freeze the bird), I may indeed want/need that (
$12,000) f/4.
I can then get the RX10-IV and use the EXACT same exposure settings, (aka 600mm-EFL f/4).
Now you are being "misleading". You seem to be implying that the same exposure will get you the same results. You are also mixing effective and actual settings to give an incorrect impression of what the results will be.
If you want to talk actual numbers, the RX10 has a 200mm f/4 lens. That's a 50mm max aperture diameter.
If your concern is the resulting image, you can match that result on a full frame with a 600mm f/12 lens (also a 50mm max aperture diameter).
Yes, you would need a higher ISO setting on the full frame. But even with that higher ISO setting, you would get the same image noise from the full frame as you would from the RX10 at ISO 100.
But if you want to use the same settings on the full frame, your full frame should also have a 200mm f/4 lens. You can then crop the image from the full frame to match your RX10, and you will get the same results in terms of image noise, depth of field etc.
Now, if you want to mislead people, you can choose to use the equivalent focal length on the full frame, but not the equivalent ISO or equivalent aperture.
I can shoot that because the lens is indeed f/2.4 to f/4.
The ONLY thing different is that I will indeed have a deeper DOF, and relatively higher-noise, (but effectively NO-noise until it becomes noticeably-objectionable).
To be fair, you could have stopped the full frame 600mm lens down to f/12. Then you would have the same depth of field, and same image noise of the RX10.
Your complaint with the full frame, is that
if you choose to use a wider aperture diameter, you get shallower depth of field.
If your concern is depth of field, why on earth would you choose to use a smaller aperture diameter?
A sigma 150-600mm f/6.3 lens for a full frame is around $850 ($899). That not only matches the results, it's a few stops faster than the RX10-IV (in this context "faster" means it lets in more total light, allowing faster shutter speeds without objectionable noise).
Again mis-leading because f/6.3 would REQUIRE (on FF dSLR) either a longer shutter-speed or higher-ISO.
With a full frame, at the same aperture diameter you would use a higher ISO. At that higher ISO the noise of the full frame would match the noise of the crop body.
As you have made clear, you are fine with that noise level.
Again, if your concern is depth of field, and you are happy with the noise level on the RX10, why on earth would you choose to shoot the full frame with shallower depth of field and lower noise?
Where are you getting the idea that you should choose the same ISO and same aperture independent of sensor size? You seem to understand that you should use a different focal length for different sensor sizes, what's your issue where you feel compelled to change focal lengths but nothing else?
(note that the obvious choice would be higher-ISO with a higher-chance of noticeably-objectionable noise)
But there is even more to the story ... because the RX10-IV lens is a ZEISS and well acknowledged to be extremely sharp, (especially at full-tele where the others tend to be softer).
It also ignores that the RX10-IV has a (unique) "stacked" sensor that enables 24fps and a (fastest in class) 9-34ms shutter-lag/Auto-Focus
No one denies that there are advantages to the RX10. However those advantages don't include deeper depth of field.
You can find a Canon EF 75-300mm F/4-5.6 for under $250. You can find third party 2X teleconverters for around $250. Combine the two, and for $500 you get a 600mm f/11 lens. That's a hair faster than the RX10-IV.
Nope .. RX10-IV is f/2.4 to f/4
And tele-convertors contribute to un-sharpness, avoid if at all possible.
To be fair wide zoom ranges (i.e. 10X), also contribute to un-sharpness. Some suggested avoiding those when possible.
Obviously, it can be more convieninet to use a built in lens with a wide range. But it's convenience you are getting, not exceptional performance.
Again, not necessarily true ... but even if it was ... "SPEED and CONVENIENCE" is a big-deal and very-very often means the difference between getting a photo when there was no-time to carry & change lenses.
Here's the deal. You seem to think that bridge cameras score better by every metric. That's not the case. They have advantages and disadvantages.
You want to point out they are convieninet. I don't have an issue with that.
You want to claim they offer deeper depth of field. That I have an issue with, because that's just plain incorrect.
You want to claim that post processing can be used to address some of the limitations of a small sensor. I have no problem with that. However, that post processing can also be used to improve images from a full frame. Thus this doesn't change the fact that the larger sensor offers a wider shooting envelope.
You want to claim that bridge cameras are smaller and easier to carry. I agree. However, I disagree that this advantage outweighs all other limitations in the general case.
Let's focus on the actual advantages and disadvantages, and not jump to conclusions on which is better for someone else.
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Personally, I think you need to think about where you might want to go with your photography, and what you enjoy. If you think you might like to try strange lenses, then you should consider an ILC. If you like playing with gear, and like being able to find the right combination of body, lens, accessories, flash, etc., then you should look at an ILC from a brand with a large ecosystem.
If you want to concentrate on your images, and not the gear, and the images you want to shoot fall into the shooting envelope of a bridge camera, then that can be an excellent choice.
I agree ...
