Well, I broke down and saved up for a Canon 6D full frame DSLR. It has a strange feature set in some ways but It seems a pretty good compromise. I was waiting for a sale and B&H had the body with a 24-105 f4 L IS lens thrown in for $1999.00 It is a good bit cheaper than the EOS 5D MKIII but the sensor seems pretty good and the high ISO performance is better than my 50D. I have a terrible time keeping up with Canon's numbering scheme I wish they had just started with 1D, then 2D and so on..... My darling wife got me the battery grip for it and it really fits my had well. It gives you an extra set of controls and grip for vertical shooting. It takes two of the Canon rechargeable batteries or 6 AA. They give you both battery trays and a soft case to hold the one you aren't using. The battery door on the camera has to be removed in order to insert the battery grip, but they provide a place to put it so you don't loose it. So far the 6D seems like a good catch.
"I suddenly realized that I knew the luminance of the moon – 250 c/ft2."
I agree the Canon EOS numbering/naming gets confusing. It was straightforward with the film cameras: Different series headed by one digit (1, 3, 5), then progressively simpler/cheaper versions of each by adding one digit (1, 10, 100, 1000). There were moments when the digital EOS seemed to follow the same pattern (1D, 5D, 6D, 7D). The constant progress in digital performance seems to have thrown that out, although generally the number of digits is an indication of where a camera fits in. It's also an indication of design as well, the fewer digits, the more robust the body and the more sensible and intuitive the controls layout. Your old 50D was the last of a special line, starting 10 years or more ago with the 10D (then 20D, 30D, 40D, 50D) with metal body and sub-professional performance. Then the 60D and 70D changed that, with their plastic bodies and Rebel features (http://www.dpreview.com/reviews/canoneos60D/). I've just moved up behind you, getting a clean and not heavily used 50D for $400.
Nikon is the same way. I lost track of what the model numbers mean after I got my D300. In the onld SLR days they came out with a new model every 5-10 years. Now they seem to change about every three months. My D300 does what I need it to do so I just quit paying attention to the marketing hyperbole.
Yes indeed, Nikon are the same. I'm just guessing, but one factor seems to be the continuing rate of progress in digital electronics, and another the availability of components (not much point in keeping an old sensor going if there's a new one with more pixels and less noise). So we get cameras with relatively brief production lives and a steady stream of new ones. Top model components gradually trickle down to "new" cheaper models.
I think it's more a matter of change for the sake of getting into our pocketbooks as often as possible. The same thing happened with computers for years. The manufacturers convinced consumers they just HAD to have the newest, fastest model. But eventually consumers discovered that they already had more speed than they could really use and they started hanging onto their gear for years. Then a lot of computer companies went out of business and the survivors slashed prices.
Same with cameras. One sensors got above 12 megapixels the average shooter will never make a print large enough for many people to tell the difference between it a a 20 megapixel sensor. And most people look at their photos on a computer screen anyway. The greatest improvements in recent years has been reduction in image noise at high ISOs and I suspect that's pretty well topped out, too. Nikon tried to cash in on the retro market with the digital versions of the F series. But from what I hear not too many folks have been willing to cough up the premium price for that model. Hopefully we're about to see prices dropping.
The digital age has brought updates every few months, but it has also brought costs down significantly. In the early 1970s a colour TV with 26inch tube was £300. For that you got a TV that tuned (manually) into four stations with an on-off switch, volume, brightness and colour controls. For £300 now you can get a 42inch TV, with teletext and all sorts of other things on board. Bear in mind that £300 in 1974 would be £2,700 at today's value of the pound.
What hasn't come down is the price of a lens of similar "size". Hence we should all be putting money into glass, and not the latest camera.
Computer-wise I upgraded my father's computer from 512kb to 1 mb about 25 years ago: the chips cost £110. For £110 now I can buy 16gb.
Do we really need the latest new equipment? The answer is no, but then we didn't actually need the old equipment either.
I don't disagree that the advertising people made big noises about megapixels and zoom ranges in their sales blurb to get people to buy the latest, much of which isn't needed (and often not as good as they claim). That said those who have adhered to film have often scoffed at digital because it couldn't resolve as many "dots" as film. Now chips are being produced that can, there is the call that it's unnecessary - and of course that is so. For most people most of the time, in all honesty, even 6 mp is plenty enough. As Sid says, newer camera have much better high ISO capabilities than older digital cameras: the latest are also much better than film achieved.
I have to agree with Dave, cameras are a lot better now but anything you buy is superseded 6 months later. The good thing is that the older models get sold off cheap. I just paid £125 for a £650 camera (2 years ago) brand new and a full warranty.
How long was the Olympus Trip on sale? or the Argus C3? Things have changed.