New member and not super techie, so please be nice. Also, I am a Tony/Chelsea fan, -- they are nice, goofy and earnest, IMHO, so again, please be nice. That said, I do get very confused by Tony's explanations. Here's why -- I think -- prior to digital phtotgraphy, using a 35 mm camera meant that light got to film causing a photochemical reaction which produced a picture. So, all the math was based on a constant. Now, there are ff digital cameras, which are "true" 35 mm equivalents and crop sensor cameras, which are camera with sensors that are smaller than 35 mm by varying degrees. In addition, the medium is not film, so instead of a photochemical reaction, the cameras are taking in information communicated by light and reacting electronically.
Since both ff and crop sensors are pocessing the same light and then electronically converting that to an image, I don't understand his comments about the same amount of light getting to the sensor. In other words, if person A is using a ff to take a picture of statue 1 with a field of view of X and person B is using a crop to take a picture of statue 1 and adjusts his position to have the same field of view of X and both are using the same lens and the same focal length, isn't everything the same? Both cameras are working to take the same eaxact picture, with the same light coming to the sensor. The only difference I can think of is that if both camera's are 20 MP then the FF pixells are going to be larger. So, I get confused about his "sensor light collecting" statements, because it seems to me that this would only be relevant if the argument was about comparing a 35 mm film camera to a smaller sized film camera. It seems to me that the argument with ff versus crop has to do with how a 20 MP ff processes the electronic information versus a 20 MP crop, not about the light getting to the sensor.
Thanks in advance for the assistance.
An awful lot of people get mixed up with "equivalent"
let's start with the crop factor... I pick up a crop camera and put a 100mm lens on it and take a picture of an object 100 feet away. Standing in the same spot, if I want to take an identically framed picture on a FF camera, I need to use a 160mm lens on it. That is your 1.6X crop factor. very easy to understand....
Things get fun when you think about depth of field..... shooting at F2.8 and at 100 feet that 160mm lens has a DOF of about 20 feet, while the 100mm lens has a 55 foot DOF... you would have to stop down the 100mm lens on the crop camera to F1.2 to get the same depth of field as the 160mm lens on the FF camera.
that's what happens if you are stationary, sometime you can zoom with your feet. If you shoot with the FF camera at 100 feet away, you can get the same field of view with the crop camera from 160 feet.... there's that 1.6X crop factor again.
If you shoot with a 100mmF2.8 lens on the crop camera and move to 160 feet with the crop camera and the same 100F2.8 lens , you get the same field of view AT THE FOCUS PLANE
, but everything else changes. Your depth of field with the FF camera is still 20 feet, but with the crop camera it is now 160 feet of DOF. To make matters even more confusing, you now have a different perspective on the two shots so they are not and can never be identical. The crop camera is now going to be seeing distant objects larger and near objects smaller in relation to how the FF camera shows them in relation to the object at 100 feet that you are focused on.
As far as light goes, that 100mm F2.8 lens remains as a 100mmF2.8 lens no matter which camera you mount it on. It collects the exact same amount of light. Your exposure times and ISO settings are identical between the two cameras. The difference is the amount of the light that is used. The FF sensor is 2.56 times larger than the crop sensor (1.6 squared). If both cameras are the same number of megapixels, this means that the pixels in the FF camera will get 2 1/2 times the light as the pixels do in the crop camera. If you are in poor light this is a big deal, but in good light it really does not matter.... it's kind of like the difference between shooting at ISO 200 and 500 (good light, not noticeable) or between shooting at ISO 10,000 and 25,600 (poor light, very noticeable difference)
and then we have the corners/sweet spot tradeoff.... Lenses are always sharpest at the center and that's the part crop used most, while FF cameras can have problems with the corners.... but since this is so incredibly lens dependant, there is no answer here....
another factor that virtually nobody considers is economy of scale and limited design and manufacturing resources. Looking at that 100mmF2.8 lens, you could design one specifically for FF and another one specifically for crop, but there would be no improvement in image quality and the price of both would be driven upwards.
In short, there is no such thing as equivalence between a crop lens and a FF lens and there is no reason to not use a FF lens on a crop sensor.