By Kaeley Kindrachuk, B.App.Sc., TechAg, Crops Extension Specialist, Outlook
Producers and agronomists are increasingly taking photos for diagnostics or posting them to social media, but not every photo taken serves its intended purpose. Good photos not only help in communicating with producers, they can also help diagnosticians identify weeds, diseases and insects. When taking photos in the field, you should pay attention to the following:
- Use high resolution – high resolution is needed for print publications. Images can be scaled down in size to meet other needs, but they can't be scaled up. Print media needs images of two megabytes or more; more resolution is needed if the image is to be trimmed.
- Stay focused – taking pictures with a phone is tricky, since the electronics determine what is important in the photo. Some phones will allow you to pick a focal point before shooting. Point-and-shoot cameras are susceptible to the same issue unless it is a "prosumer" (professional consumer) camera. If using a phone or point-and-shoot camera, zoom in and enlarge the picture while in the field to check that the photo is sharp and in focus. Nothing is more frustrating than finding out too late that your photos are out of focus and cannot be used. Bringing a laptop or iPad along can be helpful in this regard. Another option is to use a basic Digital SLR camera with a good lens. These cameras can take good print-quality pictures and allow you to manually focus on the part of the image that you want to highlight. Using a macro lens or a camera with a macro function/setting is especially helpful when taking pictures of seedlings or fine structures (hairs, etc.) on plants.
- Take many shots of each target – take pictures of the leaves, the roots, the attachment point (axils) of the leaves, the underside of the leaf, the flowers (if there are any), and fine structures like stipules or membranes. The most important part for identification of grasses is the collar region, where the leaf blade meets the sheath. Take shots from different angles of each feature so you get different light exposure and shading. No matter how many times you try, sometimes the shaky hand gets you, so be snap-happy and take lots of photos. When editing files on your laptop, be highly selective; you may end up deleting more than 80 per cent of your shots, especially if you're new to photography. After reviewing and editing the files, you can use a USB thumb drive to transfer them from the laptop for easy sharing.
- When photographing diseases, take a clear picture of the lesion and any important fungal structure(s) (e.g.: pycnidia). To help with diagnosis, also take a clear picture of the entire plant, including roots and, if possible, a picture comparing the infected plant to a healthy plant. The pattern of symptoms in the field can be very helpful in determining the cause of the disease or other damage. To illustrate this, take pictures of fields and areas of fields that are most affected.
- Scale – always include a scale reference in at least some of your shots so you know how big features were. Pennies used to be the best for this, but do not use silver coinage as a replacement. If you're shooting on automatic, silver coins may distort the exposure by tricking your camera into thinking the subject is brighter than it is. It could then compensate by making the rest of your picture darker.
- Depth of field/background – be aware of what is in the background of your shot, since it can often distract from the subject you are photographing. Shortening the depth of field (reducing the F-stop on an SLR camera) will help blur out distracting backgrounds. The smaller your F-stop, however, the more difficult focusing may become, as you'll have a smaller depth of field (portion of in-focus image) to work with.