How do you prevent Apple Photos from opening on connecting a camera.
I prefer to download all my work to Lightroom 3.
You can use Image Capture [in Applications] to dictate which photo app [or none at all] will open when you attach any photographic device, phone, camera, SD/CF card etc
I have mine set so that Image Capture itself launches when I insert a camera card, but ignores when my iPhone is connected.
[Drop menu artificially offset for visibility]
If you don’t see the options at bottom left, click the little reveal icon, circled here in red.