@aki_hartikainen must I remind you, this topic started because nobody agreed with you and every one who did learned not to. Maybe you don't really understand what crop sensors do in relation to focal length, exposure & f stop. The info is out there, though, for you to find. This topic is a flame, so it should be used as such, instructions can be found elsewhere.

"But the cropped image is smaller and needs to be magnified more for viewing. "

It does not NEED to be anything. A cropped image is smaller. Period. If you choose to use your optical magnifying glass or digital re-sizing that is up to you, but the only thing you loose by enlarging the image digitally (which might be something you want to do in post; is resolution. - or to be more precise; you do not gain any resolution by re-sizing)

@akin_hartikainen

It's not the same thing at all. The lens is what gathers the light and directs it to the sensor. The focal reducer directs more light into a smaller area, thus increasing its intensity. A sensor doesn't work this way. The same amount of light travels through a lens with a given r stop no matter how large the sensor of the camera it's attached to.

@RRRR "A sensor crop has no optical alteration. It´s is just a smaller image given that everything else is the same."

No disagreement there. But the cropped image is smaller and needs to be magnified more for viewing. Magnification has a penalty in either brightness or image quality all else being equal. The loss of brightness has to be compensated somehow and there are a myriad of ways to do it either optically or electronically. But it still has to be done.

Brightness remains equal in front of different cameras, thus same exposure for different image sizes.

I did not say it was better. I simply pointed out something that exists, even if it is transparent to the end user for the most part. But becomes visible in certain circumstances, like building a focal reducer to get increased image brightness.

I do consider getting a camera with bigger sensor but I have no need to promote such thing for whatever reason. The point is that we are not just picture snappers here, but should be able to "up our game". Not everything is always incredibly simple or obvious, but does it have to be?

Somebody clearly was on the right track at the beginning of this topic, and that got my attention. I have had this same debate a few times on different forums and I am slightly worried seeing that such large principles like crop and magnification and their effects are ignored so willingly. What else is being ignored or perhaps even denied existence ;-)

aki: you are talking about optical alteration, which normally scatters or concentrate light. A sensor crop has no optical alteration. It´s is just a smaller image given that everything else is the same.

Ask yourself this: do you think that your nikon lens image circle becomes smaller or weaker in strength just because you happen to use the centre part of it, rather than the whole image circle?

You are mixing up things which has nothing to do with the matter.

Have you ever used a light meter? Does it have options for different sensor sizes? No? Well then, there you are. They had different "sensor" sizes back in the days of film. You can easily test shooting with full frame and half frame (with the same lens, same film) if you still are intent on discussing this further. No engineers there to alter sensor / film sensitivity.

Edit: your window analogy does not work in the case of sensor sizes (as you made it out). The window is the lens. Change it however you want. Inside, on the back wall where light is reflected, it doesn´t matter if you choose a 10 cm square, a 1meter square or however big a square that can be got from the window reflection - they will all be just as bright.

I see it, but if it could be agreed that changing the window size changes exposure on the inside of the house (or camera), then we are starting to see the big picture and not just one part of it. Quite literally too.

Okay, but the histogram showed the exposure inside the house. Not outside. There was increase inside the house. Exposure outside the house did not change, however.

@tmcat but I suppose you do not deny that putting a lens in front of the house window to focus more light or growing the window size has any different effect on the exposure inside the house? Atleast I hope nobody seriously wants to refute that ;-)

@aki_hartikainen Yeah there is more light overall because you have a larger image in terms of larger FOV, so obviously there's more light captured, your capturing a larger scene. It doesn't change the exposure of any given part of that image, as is reflect by your demo photos.

@sangye The FF sensor will give an illusion of more (or less) DOF though, as there is more room out of focus and less in focus, relative to the view. I should have mentioned that, I suppose, but it's unimportant because I'm sure someone would argue that the DOF does indeed change. This is the same as what you pointed out in the demo photos, that there is more white wall to see. DOF is just easier to judge by eye than exposure.

@sangye now lets argue about whether that's a ceiling or a wall. Judging by the posture of the man, it is obviously the ceiling. It's not impossible, though, that the man is horizontal, in which case it could maybe be the wall... but it's probably the ceiling.

No, the main reason why the Black Magic Camera can produce more dynamic range, is that it has larger pixels. The sensor size REALLY DOESN'T MATTER, at all. For example, while the 5D mark II has a much larger sensor than the Black Magic Camera, the pixels are smaller, and it therefore has a smaller light-sensitive area during video recording than the Black Magic Camera. Pixel-binning would have negated that, but unfortunately Canon instead opted for the vastly inferior line-skipping method of downscaling an image, which involves ignoring most of the pixels.

The increased image brightness of using a focal reducer comes from focusing a large image protection into a smaller one, which means more photons per pixel. You could not use a focal reducer on a 5D mark II with standard lenses, because it would focus it onto just the center of the sensor, and you'd have serious vignetting. Using a focal reducer on a smaller sensor increases the brightness, only insofar as it increases the field of view. More that would otherwise have missed the sensor are focused onto it, but these photons exclusively come from the part of the scene that would have been left out of the narrowed FOV. The exposure of any given element in the scene will not increase, it's just that your scene widens. That's where the extra light goes. The real reason that the picture you posted shows a brighter histogram, is that it includes more of the white wall behind the man, due to the widened field of view.

@ignatiusreilly oh I mean @aki_hartikainen lost a whole factory's worth of marbles today...

Now that you've scared away everyone who knows what they're talking about you've only got this obstinate log to deal with. I don't think anyone should be dismissed for not understanding optical physics, as it's not particularly elementary. I do, however, think common sense denial is a deadly sin, and so I'll just quote something...

A 50mm f/1.4 will project the same image, at the same brightness, irrespective of whether it's mounted to a Canon 5D or a Panasonic GH2. The only difference is that the 5D's sensor will capture most of the projected image, whereas the GH2 will capture a smaller "cropped" section.

Nothing about this makes me think that the exposure would be different, or the amount of light absorbed by the respective sensors would change outside of the actual sensor real-estate. The only thing that changes is your field of view. And if you take a focal length reducer, attach it to that same 50mm f/1.4 and attach that newly minted 40mm f/1.4 to the GH2, you will just be allowing more light to enter, because your field of view is wider so more light is projected onto the same size sensor. The same thing would happen if you put that lens on a 5D. Lets say the differences your talking about when bringing up the f/stop, and crop factoring in were at all accurate. Then, when comparing a GH2 and 5D with the same lens, the exposure difference you'd see between the two would be similar to the difference in DOF: drastic. You're basically suggesting that arbitrary iso ratings account for the fact that it is even possible to expose an image on a non FF camera.