I love these little jumping spiders! I've recently added a tube-type light modifier to my setup which allows me to get a softer light very close to the subject. Made it from a tube of Pringles potato chips!
With more light, I can set the ISO lower: 200 for these photos, and the aperture smaller, allowing more of the subject to be in focus!
And after getting frustrated with the rear screen on the camera showing a dark, nearly useless preview, figured out how to disable that camera setting! For mirrorless cameras (a7R iii in this case) the rear LCD displays what your final picture will look like. This is a very useful feature in most situations! However, when using an external flash, to illuminate your subject, it'll display what the camera will record without the flash...a very dark image, so there is deep within the menus a setting that says "don't do that", hit that and you get a bright backscreen to set-up your shot; and the camera will trigger the flash and record the image you want!
This is why it's very hard to sneak up on a spider, the black dot is a rear facing eye!
Gear: Sony a7r iii, Sigma 105mm Macro Lens, DIY Chiptube Lightmod, Canon Speedlite 430EX II; Post: Lightroom CC