This bit:
What on earth does that mean?
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Ok for this example figures are approximate
Right. stand at a point with two cameras lets say for simplicity a FUll frame with a 300mm and a Crop with a 200m lets say we have f8
Your subject say a person is far enough to be framed head to toe
(the cameras are upright)
Take two image anc compare them -
both images are at first glance identical - a person framed head to toe in focus.
Then you look more carefully and realise that there is a telegraph pole 5 meters behind the person
It is distracting
But you notice that the FF shot on the 300 the pole is more out of focus - less distracting
Five meters behind the first pole is a second pole even more out of focus but still a distraction
You go back to the scene and re-shoot the image with the small sensor camera, having chosen a wdier aperture than the inital f8
You play with the aperture until the first pole has an equal 'confusion' to the FF image by opening the aperture
You then print the new wider aperture image
Still it is not the same as the FF image, yes the first pole and the subject look the same but the second pole is differently rendered still from the FF image -
You then go back and shoot loads of aperture combinations and realise that what ever you do you cant get the small chip image to look the same as the FF image
because the focus is dropping off at different
RATES with the different chip sizes, irrelevant of aperture
You may be able to get more blur with the Small chip by using the wider aperture but you will never get the same blur RATIOS between the different subjects
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Anyone knows that the DOF drops off faster with a lens of a longer focal lenght - look at the grass on the pitch in a sports photo say shot with a 300 2.8
If one had a 300 2.8 10 plate camera lens (Yes that lens would be the siaze of a car)
One could photograph a good chunk of the stadium (300 is quite wide on a 10.8 plate) but would still have that 'focus cut' though the grass same as the sports picture
a totally differnt look to a shot of the stadium shot say with a 35mm on a canon
S