Full Frame vs. APSC for Photogrammetry?

Full frame versus APSC is an eternal debate between photographers and videographers alike. If you want a great camera that would provide a clear benefit over using your smartphone - you probably need to get one with an APSC or full frame-sized sensor. APSC and full frame mean just that - two different sensor sizes historically established in the photography industry. Cameras with these sensors are the best you can get at reasonable prices. Let us dive into the implications of choosing a camera based on a sensor size for photogrammetry.

APSC and Full-frame

We always think that you can use any camera for photogrammetry - and it is true. But a good tool for the job is always great if we can afford one. When it comes to investing in something more dedicated, professional, and expensive than a smartphone you already have - it means we are getting serious about photography and photogrammetry. Therefore, a more informed decision has to be made - what camera should you go for?

Our short answer is either a full frame or an APSC camera. As mentioned above, these are the two widely accessible types of cameras according to their sensor size. Full frame cameras have a larger sensor, which historically mimics the classic 35mm film stock size. Full frame sensors have a total area of 864 square millimeters. APS-C sensors historically mimic a smaller negative format and have a total area of 370 square millimeters.

We talk about size because a larger sensor can gather more light while all other factors are equal. And more light - means better photo quality for the same sensor tech. This is the sole reason full-frame and larger medium format cameras exist - to provide the best image quality possible.

Crop Factor Explained

Before we examine some examples, we need to be familiar with the concept of crop factor. When a manufacturer makes a lens, its main optical property - focal length - is always shown in full frame terms. If you mount a 20-millimeter lens on an APSC camera, you must apply the crop factor of 1.5x to the focal length, making it a 30-millimeter lens on a full frame in terms of field of view. We are getting a more zoomed-in picture with the same lens. There is also the rabbit hole of aperture equivalency regarding depth of field, but this is an advanced topic for another time.

Real-world Image Quality

This is our first and most important difference - image quality. Full-frame cameras provide slightly better image quality. We made a few examples to illustrate what the differences may be. Try to find any detail or noise differences in the photos if you can. We did not manage to make good dynamic range test photos on an overcast day - but the difference is just as hard to find in real world examples. From this chart on photonstophoton.com you can find that the differnece between these cameras are around one stop on equivalent ISOs. A hardly noticeable difference in practice.

Examples are taken with two similar cameras - a full-frame Sony A7IV and an APSC-equipped Sony a6700. Technology-wise, these cameras are as close as they get, and the differences you see here can be attributed mainly to the size of the sensor.

All of the examples we used below can be found here in full resolution 80 percent quality jpegs.

Our lenses are also equivalent to each other on their respective systems. For the APSC camera, we used a Sigma 18 - 50 f2.8 lens, which provides an equivalent focal range of 27 - 75 millimeters. We used a Tamron 28 - 75 f2.8 lens for the full-frame camera. Both lenses are good and allow showing off the full sensor resolution.

Examples below are taken with the aforementioned lenses (Sigma for the A6700 and Tamron for the A7) at equivalent focal lenghts and identical shutter speed and aperture:

High ISO examples:

Other Differences

There are a couple other significant differences besides image quality that we must be aware of:

1. Lens selection. While all full-frame lenses will “fit” on APSC cameras, the opposite is untrue. Lenses designed for APSC may perform better on APSC sensors; they may be smaller and lighter, but if you upgrade to a full-frame camera down the line - these lenses will not cover the larger sensor entirely.

2. Price. Full-frame cameras and lenses are generally more expensive. Although the gap has shrunk, you can find affordable mirrorless full-frame cameras today. Good quality, feature-rich, full-frame lenses are usually quite expensive.

3. It is harder to get ultra-wide angles with APSC cameras. Due to the previously discussed crop factor of 1.5x, manufacturing an ultrawide angle lens for a larger sensor with a factor of 1x is easier. This may be relevant for those who do a lot of indoor scans, which require good wide-angle optics.

APSC or Full-frame for Photogrammetry

While this topic might be fun for us gear nerds, both types of cameras can produce perfect images for most photography use cases and photogrammetry. Many other factors will influence the success of a photo or an entire 3D scan. And the most important is always technique.

Whichever camera type you choose, learn how to use it thoroughly, and do not look back. Photogrammetry does not have any particular requirements from autofocus systems, high-speed shooting, buffer depth, or any special features. So, if photogrammetry is not the only thing you do as a visual content creator - base your decision on your specialization and utilize what you already have when doing photogrammetry. 

Conclusion

Both APSC and full-frame cameras are excellent tools for photogrammetry. If you can afford the full-frame system, go for it. If you would rather not pay for the minuscule improvement in image quality - APSC is an excellent choice, too. Most importantly, learn how to use your existing equipment and enjoy taking photos. Photogrammetry requires doing quite a lot of that.