Hi Neil,
I've used the P900 for a while now and when used to it's potential it is capable of taking some great images,like a lot of bridge type cameras on the market.Ultimately though the p900 or similar can't compete with the image quality you get with a decent dslr set up no matter what anyone tells you or what the marketing men say.
Very good point, and I fully agree!
I'd say the key to this is that a certain objective mass and bulk is going to limit your picture in some way.
The smaller the sensor, the bigger the "35 mm film equivalent focal length" of the camera becomes.
At the same time, the smaller the sensor, the poorer the quality of the individual pixel, and the stronger the artifacts from the image processing algorithms become.
The P900 accordingly the technical data goes to 2000 mm at 16 Megapixel, showing the advantage of using a small sensor.
Personally, I use a Panasonic FZ1000, which has a fairly big sensor for a bridge camera, but the downside is that its "35 mm film equivalent focal length" is limited to 400 mm at 20 Megapixel. Digital zoom will give you 800 mm at 5 Megapixel, as it's essentially the same as cropping the picture.
My DSLR is a Sony Alpha 700 DSLR with a "Bigma" (Sigma 50 - 500) lens, featuring a 750 mm "35 mm film equivalent focal length" (at 12 Megapixel).
I'd say the FZ1000 gives abot the same results as the Alpha 700 in a much smaller package, but the comparison is hardly fair as the Alpha 700 is about 10 years older than the FZ1000. I'm sure a contemporary DSLR would do a lot better.
One advantage of the FZ1000 is that it has a quick autofocus that makes it easy to take pictures of birds in flight. From what I've heard, the P900 has a bit of a hard time with that, and my girlfriend's FZ200 - which has a sensor of the same tiny size as the P900's - certainly doesn't do well in that discipline either.
So if you know what you'll be using your camera for, you can consider the trade-offs that come with size, bulk, "reach" and autofocus speed, and pick one you're going to be happy with because it does well in the things that are important to you.
Regards,
Henning