Quote: But this is not for everyday shooting now is it, we are comparing different lenses a crossed different formats and I am demonstrating why F/2.8 on a cropped sensor gives us same total light as F/4 on FF . Out in the field all we needed to know is that we have to adjust our Fstop by the crop factor to work out DOF, FOV and noise equivalents between formats
Exactly... calculations that make no difference in the field. The thing you haven't explained is why I should care about total light? You buy a camera, the first thing I advise people to do is take images at different ISOs, look at the grain characteristics and go from there. Especially form ISO 100 to ISO 400 total light doesn't mean anything to your images. But going beyond ISO 400 starts to lower your dynamic range. So in practice and I say this over and over again "total light is irrelevant, because from ISO 800 and below you get decent images from almost any camera, ISO 3200 and above you get crappy images from just about any camera but a D4s, an A7s or a 645z, where you can get decent images up to ISO 6400. SO of the range of your camera which probably goes to 25,600 ISO, 4 stops are acceptable on all cameras, 4 stops exhibit unacceptable noise which may or may not be of artistic merit. And there are two stops in question 1600 which for the sake of argument in good on FF but not on APS-c and 3200, which is degraded on both. SO of your shooting range, between of a functional 10 stop range maybe one stop is affected. The way the FF propagandists frame this you would think there is an FF advantage in noise that can't be affected. Which of course is hogwash.
Quote: I don't see why one could not crop the D810 & 80-400 to 600mm FOV and still retain a high level of detail
Andr you're bias is really showing.... in you're chart above, and people always use graphs for this because it maintains the illusion that they are talking about something important. With a graph, you arrange your axis and data to show differences In real life the differences don't look as dramatic as the graphs. IN real life you're talking small difference, not big differences. And the differences when you look at the images on Imaging Resources will back that up. But it's real world data, not made for consumers data. In actual fact, there is avery small window where FF noise is better than APS_c noise before they both become pretty much unusable.
Quote: I don't see why one could not crop the D810 & 80-400 to 600mm FOV and still retain a high level of detail
Here is where your FF bias really shows... again we are talking one stop differences here between APS-c and FF so maintaining a high level of detail isn't the point.
In the above arguments you never said "I don't see why one could not crop the D810 & 80-400 to 600mm FOV and still retain a low level of noise." Which is the same argument reversed, but is just as true. Because now we're talking about what we perceive. Not graphs where it is unclear what they represent. The simple fact is on a D810 you have a 15 MP crop file in the crop area. IN a K-3 you have 24 MP. There is a demonstrated 20-30% increase in resolution.
I don't have a D800 to use in crop mode but I do have an APS-c 16 MP camera and the resolution difference can be noticeable. Here's the image I get with my K-5 equivalent to a cropped D810,
Heres a 24 Mp K-3 images...
The K-3 is actually closer to a D810 image than the cropped D810 is to a K-3 and the D810 simply cannot match the K-3 in magnification. Cropping on a sensor with larger pixels will never provide the detail of using a a smaller sensor with smaller pixels. It's amazing how you effectively, at least in your mind argued for an often imperceptible noise advantaged. Essentially the noise under 400 ISO is pretty much acceptable in all cameras, but you dismiss a resolution gain that is available across the board in every image, as something you can replicate. But this is the basic hypocrisy of most FF advocates. They pick and choose their statistics.
And last but not least...I'd point out the ridiculousness of the DxO lens tests you posted. The lenses on DXO where the lens can be used on APS_c or FF using DxOs rating system, the same lens tests differently on different systems. Just let that sink in for a minute. One lens, different ratings. What is being tested is not the lens. It's a lens sensor combination. SO the information is mis-labelled. IN that sense the information is pretty much useless. If which lens is better depends on which system it's rated on, you aren't rating the lens. IN fact, you're rating the sensor.
Until DxO finds away to tease the characteristics of different sensors out of their rating system their system is pretty much meaningless. Test between lenses can only be compared on the same camera body. Which is in part why these test are so meanigless for Pentax users. There is a very small number of 3rd party lenses on Pentax mounts. And the information isn't consistent. For example, the K-5 is rated slightly higher than the D7000 as a sensor, but no common lens is rated higher on the K-5 than on the D7100. So for me this is the biggest problem with DxO testing. On the few places where you can find internal test points, their results are not what you'd expect them to be. They have no internal validity. As far as I can tell they are ridiculously affected by sample variation. If you go to Lensrentals.com and look at the lens samples variation, you understand that the lens sample variations from all manufacturers is dramatic. Lensrentals has good data, because they have often tested 30 or more lenses of each lens. DxO and most testing sites are doing it on the cheap with way too few samples, and their work is hogwash. Informed hogwash as opposed to outright hogwash, but just as likely to deceive as inform. How people have compared a good copy of one lens to a bad copy of another lens and come to an erroneous conclusion about the two lenses? My guess is it numbers into the millions. And given sample variation direct from the manufacturers in many cases even if thy had averages based on 50 plus lenses, they still wouldn't be able to tell you what the odds of your cheaper but better than average low cost lens might out perform a lens that costs a lot more, if you get a bad copy.
Reliance on these test sites is fraught with dangers... fraught I say...they are a guide, but they are likely to be misleading as they are to be informative, as to what your personal experience will be.