GH2 Does cropping full frame = crop sensor?
- Thread starter ralfmouth
- Start date
If I get what you're saying, there's "magnification"... so a hypothetical 16MP m43 sensor with a 2x crop factor uses all of those 16MP to resolve roughly 1/4 of the area of a full 35mm frame. To take a full frame photo and then crop with resulting identical resolution, you would theoretically need a ~64MP full-frame sensor. Of course it's not that simple with multitudinous factors of glass, processing, sensor design, and lots of other things I don't understand fully, but that's what I understand about sensor crop.
BrandonT
Well-known member
The thing that I don't really get is-- for those only interested in the film/ video use of this camera, at least-- why full frame (photo sized) 35mm is the reference, instead of Super 35mm/ motion picture 35mm film stock size? There's a significant crop from full frame 35mm size. But the difference in Super 35mm to m4/3 isn't very big.
Sorry, this probably doesn't really help you. It's just something I've been thinking.
Sorry, this probably doesn't really help you. It's just something I've been thinking.
So cropping an average full frame will have much lower resolution than using the cropped sensor. I would call that a legitimate benefit. Thx, "magnify" was a poor choice of words.
I've heard that too. Maybe people like shallow dof.
I guess, technically, you could say they magnify the image. If you took a raw frame from a 5dMk3, cropped it down to the size of a m4/3 sensor, you would find that the m4/3 sensor image has more data.
We will do some math to prove this.
5dMk3 is 5760 x 3840 at 36mm x 24mm, so pixel pitch (size of pixel) is 6.25um x 6.25um
GH2 is 4608 x 3456 at 17.3mm x 13.0mm
w = 17.3mm / 6.25um = 2768pixels
h = 13mm / 6.25um = 2080pixels
So a 5dMk3 frame cropped to a GH2 size sensor would only have a resolution of 2768 x 2080, or 5.8MP, vs the GH2s 16.1MP. ~65% less resolution. For some more fun, lets see what the sensor size comparison would be if the 5dMk3 had an ETC mode like the GH2 which only uses 1920 x 1080 pixels on the sensor.
w = 1920 * 6.25um = 12mm
h = 1080 * 6.25um = 6.75mm
d = sqrt(12^2 + 6.75^2) = 13.75mm
Using this handy table here: http://en.wikipedia.org/wiki/Image_sensor_size#Table_of_sensor_formats_and_sizes we can see that the sensor size would be in between a Super16mm sensor and a 1/1.2" sensor.
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Yes, since the sensor starts off with a smaller field of view. It is harder to get wide angle lenses.
Per Lichtman
Well-known member
Panasonic has a rectilinear 7-14mm that gives somewhere around a FOV much like a 14mm on a full-frame 35mm (though the exact FOV depends on what AR you are shooting in). It may suffer from more barrel distortion than some alternatives on other bodies, but it is certainly VERY wide without resorting to a fisheye approach.
With the 7-14mm lens @ 7mm on the GH2 you get an extremely wide shot in 16:9 mode. I don't think you can get much wider than that with normal equipment and a 16:9 aspect ratio. That will not be the case with the GH3 since it lacks the multi-aspect ratio capabilities.
Here is what the crop differences will look like between the GH2 and the GH3.
http://www.youtube.com/watch?v=zFnY5tlvW8M
Here is what the crop differences will look like between the GH2 and the GH3.
http://www.youtube.com/watch?v=zFnY5tlvW8M
All that matters is pixel density/resolution. For example the D800 has a 36MP sensor but if you crop the center of the image you still get a 15MP DX. So to say a purely APS-C camera that has 12MP has more "reach" than a D800 because it gets a 1.5x crop is completely wrong. But if you can only shoot 1080p video on both those cameras than the APS-C camera would have more reach.
BrandonT
Well-known member
Yeah, each end of the spectrum certainly has its pros and cons. As far as lenses go, the full frame 35mm has the benefit of cheaper glass for wide angle. But then for telephoto lenses, it's a lot more expensive because you've got to get-- I don't know, probably into 100+ mm? Whereas, for m4/3's "cropped" sensor, you have to get expensive-- almost specialized-- glass for wide, like the 7 - 14 mm. But for telephoto, a 50mm or an 85mm looks superb.
As far as my earlier statement, I guess probably the larger number of folks that are moving to m4/3 and doing video work came from a background of photography knowledge. Whereas I came into this after working lots of jobs on a crew using a RED ONE. So I think of Super 35mm (motion picture size 35mm) as being the reference point, whereas those coming from photography think of full frame 35mm (photo size) as the reference.
That's why I love this tool. It'll show you what the field of view is of a lens on one size sensor versus another size. It's really handy.
http://www.abelcine.com/fov/
The big advantage of a full frame sensor is that it enables you to obtain narrow depth of field with relatively slow lenses. However, this becomes a drawback when you need to shoot with a wide aperture in low light. At f1.4, for example, the DOF of a full frame lens is often too narrow to be useful. Even on the GH2, I've found the narrow DOF of apertures wider than f2 problematic at times.
Per Lichtman
Well-known member
+2 About shallow DOF and lowlight. That is one of the reasons that the 25mm f/0.95 Nokton on the GH2 is so great compared to using some of the fast lenses on a full-frame.