Choosing photography gear for photogrammetry

- [Narrator] Many different camera and lens types can be used to capture images for photogrammetry, but some will work better than others. After watching this video, you'll be able to identify ideal properties of photogrammetry camera gear. Let's talk about some basic camera specs. Really any digital camera will work just fine for photogrammetry. You're going to want something relatively high resolution, at least five megapixels, and ideally using a 50 millimeter lens with a full frame sensor. That's sometimes also referred to as a 35 millimeter equivalent sensor, and we'll talk more in detail about what that means in the next slide. Ideally you'll want a fixed or a prime lens, and that means a lens that doesn't zoom in or out. This makes it easier to keep your focal length and your field of view consistent, and that helps Metashape and its calculations as you go through your workflow. If you don't have a prime lens, your camera can still work just fine. You just want to avoid varying the zoom, so either zoom your lens all the way in or all the way out, and that keeps it consistent. Now, if for whatever reason, you're not able to avoid variable zoom, you can compensate by calibrating different groups of different zoom settings, it's just more work. Now, let's talk a little bit more about camera sensors. Different cameras have different sensor sizes, and you may hear these referred to in different ways, and we've got some examples here on the right. At the top, you'll see a 35 millimeter or full frame sensor, and that measures 36 by 24 millimeters. The sensors below are known collectively as crop sensors, and that's because they're cropping out some of the image that would normally land in the full frame area. These obviously come in smaller sizes than the 35 millimeter full frame sensor, so it's not as simple as just being able to put a 50 millimeter lens onto a crop factor camera. We wouldn't get the same results as putting that on a full frame sensor. So, we have each sensor here tagged with a crop factor and that could help us figure out an equivalent lens that we could put on a crop factor camera to get it to match the optical properties of a 50 millimeter lens on a full frame camera. So again, our ideal is a 50 millimeter lens with a full frame, and if we wanted to use a crop factor camera, we could figure out an equivalent focal length with a simple equation. We would just divided 50, that's our ideal focal length, by the crop factor. So for example, if I were using a camera with the APS-C Canon sensor, which has a crop factor of 1.62, I would actually need to use about a 30 millimeter lens to match the optical properties of a 50 millimeter lens on a full frame sensor. Now, I know this is kind of a lot, especially because we're talking about millimeter measurements of different things, so the millimeters of the sensor size don't really equate with the millimeter field of view or focal length measurement of the lenses. The good thing is we can look all of this stuff up online. None of this stuff is magic. We can look up even calculators that will do this for us. So, the thing to know is that we can't just slap a 50 millimeter lens onto a crop factor sensor camera, and expect to get the same results. Now, one additional piece of information to keep in mind if you are using an equivalent lens is that your depth of field will also change. And this actually works to your advantage because, in this case for photogrammetry, if you're using a crop factor sensor and you're using an equivalent lens to 50 millimeters, your aperture is going to actually decrease so that gives you a wider depth of field and it keeps your images more crisp and in focus. So, there are some advantages to not being able to use a 50 millimeter lens with a full frame. Last but not least, in terms of camera setup, think about how you're going to mount your camera. Invest in a good tripod. There's lots of variations out there, clips and clamps. One way or the other, you need to make sure that as you're shooting your images, things are staying still. For the most part, when you're doing photogrammetry, you're not going to be taking action shots. You're going to be taking images of things that are static. So mounting your camera frees you up to set exposure without having to worry so much about shutter speed, and that can really, really help you out in terms of getting good results as you go through your photogrammetry workflow.