I'm an robotics engineer and do not have any experience in photography. For a project, I need to take some pictures of some objects and need your experience to set the optimal setting because my configuration is not normal. I have a Canon EOS 70D with 18-55mm STM lense and the camera is mounted on a vehicle which moves! So firstly, the camera shakes alot. As I read, I need to increase Shutter speed to eliminate the effect of vibration. Secondly, the camera points the ground and takes picture of objects which are on the ground (let's assume takes picture of plants on a field). I really appreciate your comments and suggestion to set my camera setting to get as clear as possible pictures with this configuration. My priority is capturing as much detail as possible and don't need any special effect. Should I use AV mode, TV mode or manual mode? 18-55mm STM lense is useful for my application? Thank you again in advance for sharing your knowledge.
While the actual questions you asked aren't very broad in scope ("should I use Av/Tv/Manual mode?", and "Is the 18-55 STM lens useful for my application?"), I think the details of your use-case open this up to a HUGE range of considerations.
Should I use Av mode, Tv mode or manual mode?
You should use manual mode, with automatic ISO. Your primary goal is to "stop the movement" of the ground/plants zooming through your field of view. That means your main consideration is shutter speed. The faster your shutter speed is, the more it will "freeze" motion. The drawback is that decreasing exposure time will reduce the amount of light collected, making the image darker (unless it's corrected with either a wider aperture, higher ISO, more light on the subjects, or some combination of those three). See the related question, What is the shutter speed needed to stop motion?
Your secondary concern, but still important, is depth of field (What does small depth of field mean?). Based on your stated dimensions (camera can be 2–2.5m from the ground, and the objects can be as close as 20cm to the lens), you have a need for a large depth of field, or range of distance in front of the camera that is acceptably in focus. The depth of field is determined by several factors, but of them, the only one you'll have more-or-less arbitrary control over is aperture (related: What exactly determines depth of field?). Smaller apertures translate to larger depths-of-field, and larger aperture settings create shallower depths of field. Because you have a wide range of subject distances that all need to be as sharp as possible, you have little choice in aperture. You want your aperture to be as wide as possible to let in more light (to allow you to use a fast shutter speed), but you are limited to a maximum aperture size that is rather small, in order to maintain enough depth of field. See also:
Thus, both your shutter speed and aperture have hard "lower-limit" constraints. So you should select them and keep them fixed. Hence, you need Manual mode.
You don't need to control ISO; let the camera pick it for you, by using Auto-ISO. It will increase the ISO to a high enough level to compensate for a fast shutter and small aperture. That is, if there's enough light shining on your subjects.
Some issues that you will have to contend with: I mention these issues here so you can begin thinking about them, and formulate new questions to ask. Complete answers to these issues are beyond the scope of this original question.
Minimum focus distance of lens: The 18–55mm STM lens has a minimum close focus distance of 25 cm, measured from the camera's sensor plane (What is the reference plane used when the minimum focus distance is measured?). You stated that your subjects might come to within ~20cm of the camera. To be specific, as long as the subjects come no closer than 20cm to the front of the lens, then the lens length plus camera body thickness combined will put your camera's sensor plane more than 25 cm from the subjects, thus ensuring you don't come within the minimum focus distance.
Probably will have to maintain constant (fixed) focus (no autofocus): At a worst-case speed of 15 mph, the ground is across your field of view at 6.7 m/s. With objects moving quickly through the field of view, at such greatly varying subject distances (a range of about 2m), your camera's autofocus won't have to time to even find something to focus on. And that's ignoring the lens's autofocus motor speed, which isn't particularly notable for that lens. So you will need to determine a fixed focus distance, tape down the focus ring, and set the body to Manual Focus mode.
Depth of Field Limitations: At 18mm, the most depth of field you can theoretically achieve is with an aperture setting of ƒ/22 (the smallest aperture for your lens). But that will only yield a depth of field from about 30cm out to 1.1m (a DoF range of 0.8m). Your only option to achieve a DoF of at least 2m is to restrict the subject's closest distance to 35cm or greater. However, nothing is free in photography...
Diffraction at small apertures: By stopping down to ƒ/22 to achieve greater depth of field, you are well within the diffraction limit of the lens, which causes some fuzziness and loss of detail (see: What is a "diffraction limit"?). When diffraction is factored into the depth of field calculation, beyond about ƒ/8 to ƒ/11, your increased depth-of-field is offset by loss of detail caused by diffraction. At ƒ/8, in order to have a 2m depth-of-field, you'll have to raise the camera to 3m above the ground, and focus at a point 1.45m below the camera. This leaves no margin for vertical travel, etc.
Lighting: For example purposes, let's assume you use your fastest shutter speed of 1/8000s (the choice and calculation of which is important, but this answer is already too long). At that shutter speed, with the camera moving at 15 mph, movement is stopped to less than 1mm for the duration of the exposure. At ƒ/8, that equates to an exposure value of 19. For comparison purposes, a scene lit under sunny bright conditions has an EV of 16. The difference of 3 stops (19 – 16) is the amount that ISO will have to compensate for to have a nominally "correct" exposure. Under these ideal conditions, your camera's Auto ISO will select and ISO of 800. Thus, under natural lighting, bright sunlight, the lowest ISO you can use is 800. All other natural-light conditions will require higher ISO. Your camera will go as high as ISO 25600 (although from my understanding, you probably won't want to go beyond 12800 due to high-ISO noise). 12800 is only 4 stops more than ISO 800, which means that with a fixed shutter of 1/8000 at ƒ/8, your Auto ISO will only have about 4 stops of range to compensate for changing light levels.
Note also that shooting straight down at vegetation is noticeably darker than shooting a typical scene parallel to the horizon with sky in the background. Thus, the stated ISO 800 above is theoretical ideal. Likely, on the brightest day, when shooting straight down at vegetation, your camera's Auto ISO will probably be picking around ISO 1600. Therefore, if your conditions are anything less than bright daylight, you will probably have to plan on adding artificial light sources to your scene to control the exposure.
18-55mm STM lense is useful for my application?
Yes, and no. It sounds like you are in the preliminary stages of this design. You are just going to have to do some prototyping, and quite a bit of trial-and-error, to figure out what's going to work and what won't. For prototyping purposes, the 18-55 STM is a fine choice for two main reasons:
It's cheap. Cameras and lenses are sensitive equipment. SLRs especially have lots of moving parts. The vibration might shorten the lifespan of the lens, so being to replace it at low cost, especially in the prototyping stage, is probably important.
It's a zoom lens. You'll probably use the wider end of the zoom range (18mm) rather than the narrow end (55mm), but it will probably be helpful during the prototyping stage to be able to tune your focal length.
However, once your parameters are dialed in and you are out of the prototyping stage, a zoom lens is probably not optimal, because of the mounting position. Mounting the camera pointing straight down, in a vibrational environment, is the absolute worst configuration for a zoom lens, when it comes to stability of the setup / fixing the focal length. This is because the lens's zoom elements move longitudinally along the the optical axis, which in your case is straight up and down. The constant vibrations will act to pull the zoom element downwards, changing your focal length (your zoom amount). You will have to tape down the zoom ring to prevent it from being turned by the weight of the vibrating zoom element.
Unfortunately, while a prime (fixed focal length) lens would probably be better than a zoom, from a durability and simplicity standpoint, the 18–55mm STM is probably the best tradeoff between wide-angle and price.
During your prototyping, you might find that 18mm doesn't give a wide enough field of view. In that case, you have some limited options:
- The Canon 10–22mm USM probably has a more useful zoom range for your situation, but it costs 2–3× the 18-55mm STM.
- Sigma's 10–20mm ƒ/4–5.6 EX DC HSM is about 2/3 the price of Canon's 10–22mm.
- Tamron's 10–24mm F/3.5–4.5 Di II is priced between Sigma's and Canon's lenses above.
There are other options, as well as some wide-angle prime lenses, but just about all of them are more expensive than the above lenses.
scottbb has more than adequately covered the pure photography side of things, so I'd like to add another aspect.
Bouncing a camera repeatedly over a bumpy field on a hard mount & expecting it to last more than a week is going to be an expensive learning curve.
I'd see the three main points of potential failure to be -
The lens elements being shaken out of alignment
The lens/body coupling being distorted or broken &
The mirror being misaligned or detached.
I would seriously consider investing in some sort of camera stabilisation mount.
I work in Film/TV but not as a cameraman, so I've seen a lot of these in use but don't have any specific recommendations.
Steadicam is the usual generic description, but it's a trademark, so it's like trying to find a Dyson by Googling 'hoover'
So, Googling "camera stabilization vehicle mount" will bring up many options, from maybe $£€ 500 upwards, probably closer to 1000-1500 before you're starting to reach 'professional' quality, & onwards up to 100-150k for something you can safely hang a 70mm movie camera from.
I'd consider that one approximately the value of the camera & lens would be a reasonable investment.
You can also rent this type of thing.
Another huge plus point is that it will also stabilise the pictures.