I have a Nikon D850 with portrait lens AF 105mm f/1.4. I'm just learning how to make good pictures. We purchased this camera not for business — we have kids and want to make every possible memory. I'm using A mode, but often when I make pictures, one kid's face is in focus but another one is blurry. (I have twins so it rarely happens to get a good picture with both kids in focus).
What setting do I need to change? Kids birthday is this weekend and I'm the one who will take pictures of all kids.
I normally don't recommend buying things, but, here, there are two bits of equipment which will make a world of difference.
First, get a wider-angle lens — 50mm or 35mm or somewhere in that range. The 105mm portrait range is great for isolating individuals, but not so great for "lots of kids", both just because the framing is tight and because the framing will tend towards not very much depth of field. (See What exactly determines depth of field? and Why is depth of field affected by focal length?)
Second, get a flash — something low cost that you can use off-camera. The Godox and Yongnou systems are great budget options, or you can go within Nikon's own system. This is essential because in order to increase depth of field, you'll want to stop down the aperture, which means less light. A flash will give you that, allowing you to stop down without going to slow shutter speeds and high ISOs.
Many people are shy of flash ("I prefer natural light!") because they've had or seen bad results with on-camera flash. Getting the flash off-camera (preferably with a radio-based system — these are very affordable these days) is a world of difference. It does force you to be more aware of light, but that's a good thing for improving your photographs anyway.
You need to change the aperture. Narrow it down! Narrow it down a lot!
I don't think your portrait lens is a good idea for taking pictures of lots of kids. It's designed to blur the background so that the viewer's attention is directed to the main subject of the photo, the photographed person. If there are lots of kids at various distances, you can't make all in focus with the F/1.4 aperture.
Also, 105mm is rather long focal length for taking pictures of lots of kids, even considering your full frame sensor. You need to step back. In fact, you probably need to step back so much you'll hit a wall if you're indoors!
But, nothing is impossible. Use something like F/10 - F/16 aperture and you'll suddenly see your depth of field will become much better. On a full frame camera, F/16 will probably work much better than F/10. Also, stepping back will help you increase the depth of field.
Use the aperture priority mode of your camera, and set the aperture to something between F/10 - F/16.
Also, such a portrait lens may lack image stabilization. At the 105mm focal length, it's definitely a problem. If you need to take the picture really quickly, honestly, you would be better off with a kit zoom with narrow maximum aperture opening and image stabilization. Example of such a lens: Nikkor 24-85mm f/3.5-4.5G ED VR.
Now, if the kids are moving fast, then image stabilization won't obviously help to freeze the movement.
(Edit: I originally suggested F/5-F/10, but after consulting a depth of field calculator, even as large F-number as F/16 might be problematic with this lens at close distances. The full frame sensor, and the long focal length make the depth of field very limited.)
Use A set to 5,6 or 8
A wider lens 35mm will do that better
The 105/1.4 is for ONE subject making everything else as blurry as possible (when set to .4) It would be hard to find a lens that makes more things out of focus
This lens is VERY expensive because it CAN do this At f/8 you will have lots in focus
F/11 is probably your max number for A (aperture setting)
