What is full frame and why is it a reference?
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| source: https://petapixel.com/color-photography/ |
In a nutshell - Full-frame was a popular film format, 36x24mm in size. That format carried through to today's professional digital cameras. Lens focal-length equivalence is often used because the same lens will give different compositions on different cameras. Discussion among photographers involving lenses would bring up full-frame equivalent focal lengths. This way, photographers using any format could follow along.
Kodak introduced "135" film in 1934 as a standard film cartridge. This film records images at 36mm x 24mm. By the 1960s, it was the popular standard. This popularity continued till the advent of digital photography. It left us with the common idea of the "professional" format - Full Frame - using these dimensions. The next major competitor is APS-C - a similar rectangle at 2/3rds the side length. Micro Four Thirds is another format even smaller than APS-C. By the time the digital age was upon us, 35mm film/cameras/lenses had dominated the industry for decades. Cost and technical difficulty propelled smaller digital sensors into lower-tier consumer markets, with the expensive "Full Frame" sensors directed to professional or higher-end consumers.
A given lens will create an image when focusing on a medium. The image can be recorded on photographic film or a digital sensor. If you're curious, you can hold a lens near a window, and hold blank paper behind it. Move the paper close to the lens until the image is in focus. You should see an inverted circular image of what's outside the window.
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| Holding my Nikon 50mm and trying to focus it on this pad while taking the picture proved quite clumsy. |
A full-frame camera would render a picture as if drawing a 36mm x 24mm rectangle in that image. An APS-C sensor is about 24x16, and would be that smaller rectangle. A M43 sensor would be a 17x13 rectangle in that image.
FOV Equivalence:
Right away the idea of smaller sensors being crops of the full-frame image should come to mind. It's a tighter field of view - so how can you get a similar picture? The main idea of equivalence should be about framing your shot.
Let's assume that you liked 50mm lenses on full-frame cameras. If you picked up a micro four-thirds camera, what lens would give you a similar feel? Well because of the smaller sensor, you will need a wider lens. 25mm is quite close. If you were looking for a lens on APS-C cameras, you'd need 35mm.
This is where the idea of crop-factor comes into play. It is the ratio of the sensor's diagonal, comparing the full-frame sensor to the cropped sensor of APS*/M43 and other sensors.
APS-C has a crop-factor of 1.5 (in general - Canon does 1.6). Micro four-thirds has a crop factor of 2. These numbers can be used to quickly figure out equivalent focal lengths on their respective systems.
Most smartphone cameras have a crop-factor of 5 or 6.
Depth Of Field Equivalence:
If I composed a shot on the full-frame A7II, then with the same lens I'd need to recompose on the smaller sensor Panasonic G9. I'd have to step back because the lens has a narrower field of view on that smaller sensor. If you step back, you increase the depth of field.
If instead I switch to a wide lens to compose the image in the same place? Wider lens, increased depth of field. The only way to frame it and get the blur right would be to use a wider lens and faster aperture.
If I wanted to blur the background of an image, and I shot 50mm F2.8 on the full-frame camera, I'd need to shoot 25mm F1.4 on the Micro four-thirds for the same shot. If I shoot 50mm F1.4 on the full frame, I wouldn't be able to copy the depth of field at that composition, because I'd require a 25mm F0.7 lens for micro four-thirds.
This will matter more to photographers using fast zooms, for which there are few equivalent options in crop sensor formats. A 2.8 zoom can still give great subject isolation and background blur on a full-frame camera. The equivalent would be an F2.0 zoom on APS-C or an F1.4 zoom on micro four-thirds. Lenses with those f-stops don't really exist (OK.. Sigma's F1.8 zoom and Panasonic's F1.7!) but some primes can deliver enough blur - or just shoot differently. Nobody says you must take every type of shot, with every camera.
Depth of field equivalence is usually not as important as some make it appear:
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| Canon 55mm F1.2 S.S.C. FD remounted to EF on Metabones focal reducer, 39mm F0.86. |
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| Nikon 35mm F1.4 AI-s, adapted to Canon EF, on Pixco focal reducer, 25mm F1.0. |
FOV Equivalence Table:
