Here’s How Digital SLR Sensor Crop Affects Your Lenses
If you’ve worked with digital SLRs in any capacity, you’ve probably heard the question, “Hey, is that a full frame camera?”
If it isn’t, you’ll usually hear, “Oh. Well. You should consider getting one.”
The reality is that full frame sensors aren’t necessarily always superior, despite their price tags and comparisons to the 35mm cameras of yore. In fact, most of us own cameras with smaller cropped sensors, which artificially increase focal lengths on full frame lenses.
What Is A Full Frame Sensor?
Full frame sensors are essentially the evolution of 35mm film – the format is based entirely on the traditional frame on a 35mm roll. A full frame photo takes up the entire size of the sensor, allowing for usage of all real estate available (save for the circular crop that all lenses produce).
An S35 camera sensor (say, on the Canon C300 – a cinema camera) is going to be slightly cropped and produce an image comparable to what you find on a cropped sensor DSLR (also known as an APS-C sensor). Granted, something like your Canon 5D Mark III is definitely full frame.
What does this all mean?
Basically, it’s the standard sensor size among professionals. When you hear someone talk about a 50mm focal length, they are talking about what a 50mm focal length looks like on a full frame sensor. Cropped sensors of the APS-C variety don’t take in as large of an image, only using what the sensor can see. The APS-C sensor is at around a 1.6x crop, effectively turning a 50mm lens into an 80mm lens.
Using a full frame sensor allows more light into the camera, provides greater real estate in terms of a bigger viewfinder for framing your shot and often allows for a shallower depth of field (for a stylistic look with lots of bokeh).
The two main sensor sizes you should keep in mind are full frame and APS-C. Below is a very handy image from Wikipedia showing a comparison of all sensor sizes, and you’ll even notice the APS-C size has a slight difference among brands.
So… What About Cropped Sensors?
Does this mean cropped sensors are bad? No. Are they lower quality than full frame sensors? No. They are just smaller sensors, that are cheaper to make but effectively yield a similar, usable image. They are smaller than full frame sensors, and as such do not make use of the full field of view that lenses provide.
As such, you can get a cropped sensor camera for a pretty affordable price compared to something like the Nikon D810 or Canon 5D Mark III.
Cropped sensors don’t perform as well in low light as a full frame camera (though age and purpose are contributing factors) and they typically don’t yield as shallow a depth of field. As less light enters your image via a smaller sensor, there’s the possibility (in low-light situations) for grain or noise. However, with good lighting through the use of fast lenses, the image quality can be virtually the same.
On an APS-C sensor (such as on the Canon 7D Mark II, 70D, or T5i) a 50mm lens will be an 80mm lens. Furthermore, lenses made specifically for APS-C sensors aren’t going to work well on full frame sensors. They are going to vignette or show the full circular image that the lens provides – though some manufacturers (like Nikon with its DX range) automatically adjust newer cameras for these older, smaller lenses.
Below is a video comparing cropped sensors and full frame ones. Yes, it’s pretty noticeable, but the image quality (even with the DOF comparison) is relatively the same. Basically, just move farther away from your subject when using a cropped sensor – you’ll be fine.
And What About Cinema Or MFT Sensors?
If you work with video, you probably know about S35 sensors. They are also based on 35mm film, but they are cropped to fit the size of standard film aspect ratios (typically 16:9 for today with options to view things in 2:35:1 or 1:85). In the end, if a cinema camera has a S35 sensor, it likely matches a APS-C sensor a bit more closely. When working with cinema cameras, follow the APS-C guidelines. Granted, we all know DSLRs are often used to make videos and film these days .
MFT (micro four-third) sensors are an entirely different ball game, though. They are typically found on mirrorless cameras, not digital SLRs. Those sensors are tiny, and they effectively double your lens focal length. That means a 50mm lens will be a 100mm focal length. Cameras like this include Olympus PEN cameras and the Panasonic GH series.
You should also factor in the aperture size when talking about MFT sensors. There’s a bit more blur with larger sensors, so an f/2.8 aperture on a full frame sensor is going to look different than one on a MFT sensor. It’s not a huge issue, but the video below touches on that.
Large & Medium Format
There are such things as larger digital sensors than those based on 35mm standards. In cinema, there’s the 65mm sensor, and film goes even beyond that. We won’t exactly get into the “crop factor” of these sensors since they are bigger than 35mm. If you were to put a 35mm-based lens on a 65mm sensor, the image will be cropped much as if an APS-C lens was placed on a full frame camera.
In the above image featuring sensor comparisons, you’ll see the medium format size compared to the rest – things can get pretty big.
But What About Quality?
In the end, there’s not automatically going to be a reduction of image quality when it comes to sensor sizes. The greater the size of the sensor, the greater the field of view – it’s as simple as that. In theory, you could just step back if the image seems larger on your APS-C camera… there’s really nothing to worry about.
Below is a nice comparison between cropped and full-frame sensors.
Which would you choose: APS-C or full frame?