You already have a lens system which is optimized for 35mm. Every glass in your range (except for newly introduced glass, like the EF-S and DX) delivers an image circle for a 35mm frame. I would argue that EF-S and DX is a kludge, definition of a kludge being "an error introduced to fix another error". If Hasselblad wanted to produce a digital back for its MF camera, would it buy a 6.0MP APS sized sensor from Sony? The answer is "no" for many reasons, but one of the prime reasons is because too much of the imaging circle has been wasted. The argument remains true, in a smaller scale, for FF vs. APS sized sensors.
Agree that glass is for 35mm format, but it's glass I already bought, so it's not an added expense.
Actually, medium format backs haven't until very recently been approaching full frame. For a long time, the most popular Phillips chip for medium format backs was actually 35mm sized (ie 36 x 24mm). So there was a lot of wastage, and it was even harder to get true wide angles given that it is far harder to get ultra wides to fit medium format cameras compared to 35mm systems. There is a lot more wastage in using a 36x24mm chip in even a 645 system, compared to an APS in a 35mm. So your point is flawed and actually does much to undermine your argument!
Expanding on my first point, the greatest expense in designing a lens is to ensure the lens performs consistently from corner to corner at wide apertures. This is one of the touted advantages of DX/EF-S/Four-thirds lenses. Paying a small fortune for a 600 F/4 and then throwing away the most expensive part of the image sounds wasteful to me.
At the same time, knowing that you have a DX size sensor could save you a bundle of money. If you knew you'd need a 600/4 on full frame, but now had a D2x, you could buy a 300/4 on the crop mode (assuming 6.8 mp is sufficient), and save about S$12000.
Furthermore, it doesn't matter how well you design a lens, it's corners and edges *always* perform worse than its middle. By using a full frame lens on a full frame camera, or a DX lens on a DX camera, your corners and edges suffer from quality deterioration. If anything, the only way of achieving a lens that performs consistently "from corner to corner at wide apertures" is to actually use an oversized lens. For instance a full frame lens on a DX sensor... take the difference between the Nikon and Sigma 12-24 lenses for instance.
So in response to your points, you might be throwing away the corners, but the corners are poorer relatively anyway. And also, if you've already bought the lens, great, it's no real loss to you since you bought it for what it was. But if you're contemplating a lens purchase, having a smaller sensor can save you plenty of money since you could realise you don't actually need to plough all that money into a 600/4.
Also in exchange, you get better resolution, less (if not any at all) light fall off at wide apertures, and less distortion and aberration.
To continue along this line, where are the savings which reduced crop lenses have promised us?
Actually, there is a lot of confusion in this area. At shorter focal lengths, you don't actually save much glass so there shouldn't necessarily be much cost savings. As you've demonstrated, the DX lenses are about the same prices as their non-DX counterparts. But then this isn't in any way a criticism of DX lenses... they are not any more expensive than their full frame counterparts either, so full frame isn't better either.
That's on a one to one comparison. But I've always held the savings come when you put together a basket of normal lenses, and price it up as a whole.
Say you want to get from 20mm through to 300mm with a constant f2.8 aperture.
With full frame, say you get 20/2.8, 24-70/2.8, 70-200/2.8 and 300/2.8. Total cost about S$13500 at a very rough approximation.
With DX, say you get a 14/2.8, 17-55/2.8, 70-200/2.8.
Total cost about S$7000 at a very rough approximation.
... I am sure you will agree there is no difference. We are still paying the same price for reduced crop lenses as we were for full frame lenses.
Nope, agree, the difference will come in longer lenses, if Nikon ever bother doing that. I cringed when the 200-400 and then the 200/2 were full frame, don't look at me. But as you yourself say, it's not any more expensive either, so this is not 1-0 to full frame, it's more a halve, to borrow Ryder Cup speak.
Among other things, sensor designers are concerned about resolution, dynamic range, and noise suppression. Pixel pitch (the size of each individual photo pixel sensor, in micrometers) is just one out of many factors which influence these.
But as you say, it is just one of *many* factors that influence these. Having a smaller sensor means a lens has to cover a smaller image circle, which in turn means that manufacturers can make higher-resolving lenses as they have to spend less effort correcting for aberration, which in turn eliminates any issues with resolution problems. With regards to noise suppression and dynamic range, with an equivalent lens, I agree completely. However in theory DX lenses *could* be designed a stop faster than their equivalent full frame lenses, for the same size, weight and price (excepting initial R&D considerations). That it isn't being done is a source of much grief to me.
But clearly we are not yet at the technology threshold yet either at the moment, which will also no doubt continue to improve. Any claims that Nikon cameras suffer from poor noise levels compared to their Canon counterparts due to the DX sensor is missing the point. Clearly chip technology is at the heart of any problems. The D1x for instance, has a smaller photosite than the 1Ds, yet has clearly better noise characteristics.
Canon have shown with the 20D that they can get 8 million pixels into a DX sized sensor to even greater effect than the 8 million in a 1.3x 1DII sensor.
Another factor is that microlenses really prefer light to be hitting them as close to perpendicular as possible. This has always been a problem with full frame chips, as obviously at the edges and corners light strikes at an angle. This results in light fall off and chromatic aberration around the edges and corners. And was one reason why Kodak decided to leave microlenses out of their Pro 14x series (the others we won't go into!). So a full frame chip, ceteris paribus, has more optical problems around the corners and edges as does a DX sensor.
A full frame sensor ultimately allows you to fit more, and larger pixels. Eventually you will hit a limit on a smaller sensor before the conflicting demands of resolution and larger sensors force you to look at other means of increasing dynamic range and reducing noise. You just hit the limit later on a FF sensor.
Agree that obviously you will be able to fit more larger pixels on. But as mentioned, in theory you should have a 300/2 on a DX at ISO 100 as opposed to a 300/2.8 at ISO 200 for instance, which is exactly the situation back at square one.
And clearly you can get 8 million pixels into a DX sensor (20D) with stunningly good results, as you yourself regularly attest. So clearly there aren't major issues yet. And we are really at the stage where the vast, vast majority of photographers do not need an ounce more resolution. In fact we were there with 6mp, never mind 8mp.
I am no in any way saying we don't need more resolution, but I'm talking in practical terms. There used to be the days when everyone sung the praises of Velvia. For that, you had to tolerate ISO 50 and no exposure latitude, and very contrasty (ie poor dynamic range) images. Colour aside, the previous generation of 6mp cameras gave you all that with a far greater ISO range.
I have images from a D1 done to 6m x 4m and they look great; images from a D2h done to 3' x 7' and they look terrific too. Critically examinging D1x files to 24" x 36" they firstly look sharper than tranny stock, and secondly look absolutely fine. Sure a 11, 12 or 16 mp file will look better, but if you don't put them side by side, you wouldn't in any way complain about the 6mp file (for most applications).
Viewfinders. Its not strictly necessary to have a larger viewfinder - it's just nice to have.
Agree completely. Full frame cameras have got bigger viewfinders.
Other factors you've forgotten:
You've gone on about DX lenses not saving money. I suggest they do. And you've completely forgotten than DX *cameras* are significantly cheaper than full frame cameras. At the anticipated street prices, you could nearly afford two D2x bodies for the price of a single 1DsII.
While it hasn't happened yet, primarily because Nikon are sadly still committed to full frame lenses on their digital cameras, a smaller sensor means the camera could be made smaller as well. A smaller, lighter system (including lighter lenses - look at the E series), is a welcome boon to *all*. I know a die hard Canon fan who keeps whinging about the size of cameras. Better on your back, and more likely that you will have your camera with you rather than sitting in your dry cabinet at home.
And I'm also too lazy to think, but I think there's just a lot of inertia in resisting the legacy that is full frame. It's like paper sizes. There is no real reason for the industry to stick to 4x6, 5x7, 6x8, 8x10, 11x14, etc, when there is no convention to the sizes and no relation, and the most common film format was in 3x2 dimensions, only really fitting the 4x6 paper size. The rest are leftover from when 4x5 was the neg size, or other formats. The A4 system is actually a much cleaner naming system, with a clear relationship between A0 through to A-whatever, and with much less paper wastage than an 8x10 sheet using conventional 3x2 dimensions.