Any camera can make useful specimen-images.
The value of specimen-images is greatly increased by attention to some small details.
Warning: I am not a photographer. These notes are to help you understand what to look for when looking into imaging equipment. I have included links to potential choices in the US. Again, their primary purpose is to help you when talking to a source in your own country.
General comments: Any digital camera can be used to image specimens.What differs is how the resulting images can be used. High-end equipment will record images that allow zooming in on details, much as one does with a microscope, but images made with simple equipment, such as those used for images shared via social media, will enable remote data entry and creation of a catalog of your collection. Whether they can be used for confirming, questioning, or rejecting an identification depends on the taxon involved, the quality of the specimen, as well as the the imaging equipment used.
Selection criteria: Images made with high-end camera-lens combinations will have parallel edges, be in focus for the whole specimen, render the specimen’s colors accurately, and make it possible to zoom in on small features. But high-end camera equipment is expensive, and the image files large. Large files take a long time to download, making them impractical for many uses. Smaller Images, including those made with simple equipment have value, as explained in the previous paragraph and they will download rapidly.
What should you do? Acquire the best combination of equipment your budget permits. Large image files can be reduced in size; the reverse is not true. If, for now, you can only afford inexpensive equipment, purchase that, following the advice given on the instruction page to make the images as useful as possible. The images will aid you in planning field work, becoming familiar with the taxa, and in summarizing your holdings. Whether or not the images can be used to confirm, reject, or query an identification depends not just on image quality but also on the taxon and the quality of the specimen.
Reducing image size: Many programs exist for reducing the size of an image file, but when imaging a herbarium collection, the best option is a program that will scan the images in a folder, rename each one to its barcode (e.g., from img123.jpg to UTC032983.jpg), and then generate smaller images. For posting to Symbiota networks, such as OpenHerbarium, there is a free program for generating the three file sized used by the program. The smallest files, “thumbnails,” are about 8 Kb and are used, for example, in the listing for records returned by a search. Mid-size images are used for routine displays and are about 250 Kb. The largest, which are only displayed if requested, are about 2500 Kb. The source herbarium is expected to store the original files. They can be stored on external hard drives or on a local server.
Specific equipment. The following comments are intended to help you talk with appropriate individuals in your own country.
Cameras: Purchase a camera that allows you to purchase the lens separately. This will allow you to select the best lens for imaging herbariaum specimens, not one that is good for many purposes but not as good as it might be for any single purpose. Desirable features include a large recording area (sensor size) that enables you to record a larger image. This tends to permit more accurate focusing across the whole of the field of view. It should be combined with a high quality macro lens. Images that are over 20MB allow printing a full-size image of the specimen at 300dpi, a typical resolution for print media. But how often will you want to do that?
Lenses: Look for a macro lens that will allow you to image the whole specimen while keeping the camera-specimen distance at or below 1 m. Macro lens minimize the tendency of straight lines away from the centre of a flat object to appear curved and and color aberrations (the tendency for out-of-focus items to have a color fringe (see “bokeh”) https://en.wikipedia.org/wiki/Bokeh). Keeping the required camera-specimen distance below 1 m refocusing the camera easier, and the focus should be checked about once a month. Another desirable feature is auto-focus. Lens with autofocus will be able to adjust for differences in thickness among specimens. Image stabilization, important when a camera is held in the hand, is not important in cameras being used to digitize a collection. Instead, purchase a good camera stand (not one that is on a spring-loaded clamp) and remote shutter control to eliminate operator-induced movement.