I think you missed the post gene made earlier Tony Northrup misunderstood DXO's data, says who DXO.

secondly his Aperture calculation makes no sense. He was quoting an f2.8 becoming an f4.2 f4 is a stop different from f2.8

So you attach the f2.8 to say a d750 you take a photo lets say 1/125 at iso 100
repeat but with a D7200 at the same target and light level and aperture the f2.8 has become f4.2 so now you need over a stop more light and the new exposure would all things the same apart from the sensor size be 1/60th or there abouts at iso 100.

This is not true the same light is entering the lens more of it is off the sensor but it is at the same density over the sensor.

The main difference between a crop sensor and a full frame sensor is magnification. Normally on a full frame sensor printing to say a 6 by 4 card you would only enlarge so the edge of the recorded image reached the edges same as for a crop sensor If we crop the full frame image down to the same field of view as the crop sensor and print that then the two images would be identical. There can be differences in pixel size between each camera but it isn't visible with the naked eye. The apparent depth of field is only changed by the magnification of the print.

Lets borrow Rons D810 to take a picture of this parrot a norwegian blue, wonderful plumage and now lets switch modes from fx to dx. Did you see it move? no, its just how it was. Switch to fx any difference? no the same number of pixels on the sensor are covered with bits of parrot regardless of fx mode or dx mode. As far as the fx image and the dx images are concerned the fx image shows more background. Not even a difference in the viewfinder.

provided we don't move the camera there is no change. (we don't have to worry about the norwegian blue moving its nailed to its perch).

I rest my case. Tony Northrup is wrong about this.

Blackest, TN is not completely wrong in suggesting that you need to take into consideration the Fstop of the lens when making comparisons for "light gathering" between L and crop lenses, but not with regards to brightness at the sensor. For the most part it is safe to assume that placing an L lens set to F2.8 on a full frame camera, then remove the camera and place a crop sensor camera, the crop sensor will not see "less light" which would mean you'd have to adjust the fstop to change the amount of light hitting the sensor. But, if you want to make an overall comparison, taking into consideration the depth of field, then it would make sense if you are comparing lenses with equivalent angles of view. If you have a full frame camera fitted with a 150mm lens the angle of view is similar to a 1.5 crop camera fitted with a 100mm lens. But the 100mm lens being a shorter focal length, at the same distance (point of view), will have a greater depth of field. The 150mm at F4.2 would have a similar depth of field to the 100mm lens at F2.8. Obviously you would have to change the exposure value (increase either the ISO or the open shutter time) to make up for the smaller aperture.

TN and others try to wrap their non-technical heads around these concepts and need to make stuff up, and make dubious at best assumptions like this one where somehow DoF is somehow related to image quality, and that is somehow related to sensor size and light falling/not falling on a sensor somehow affecting the image quality. It's not that hard to figure this out, and even easier if you put away the slide rule for a moment (am I showing my age? did I really write slide rule?). I agree, with regards to light and sensor size, he is 100% wrong when he states that the cropped sensor lens is somehow better than the L lens. But his depth of field comparison does make sense but only for depth of field of two different lenses with equivalent fields of view.

Admittedly this is a side-trip, but why do we use the term "cropped sensor camera" (yes, I use it too)? Thinking about it, it occurs to me that all sensor or film sizes are cropped in comparison to larger sensor or film sizes. I have both FX and DX cameras. The DX is cropped in comparison to the FX, and the FX is cropped in comparison to a medium format sensor, which is also cropped compared to a 4x5 view camera, etc. Wouldn't it be simpler to refer to the specific sensor(s) in question? Calling one sensor size "cropped" implies that the comparator sensor is not cropped. Both my cameras are "cropped" in comparison to ones with larger sensors.

Now I've got it? Again you come across as condescending. Again you feel the need to correct someone. Just because something seems "incorrect" to you doesn't mean that you need to correct people over because it's not your opinion. Dont speak just to hear yourself talk. You interrupt a thread just to show how much you know by acting like if you don't clarify something, everyone else will not be able to reach their own conclusion. I don't need a translator. If someone has questions they will ask. then you can amaze them with your keen sense of crop sensors. In the mean time please don't comment on my posts again if you feel the need to clarify my statements. YOU DON'T.