What camera? The camera can only focus on one plane at a time, it will generally focus on whatever is closest to the camera in the set focus area. It is up to you to make sure that both individuals are in focus, either by position or by increasing the depth of field.
Note that this was what Canons late A-Dep mode was for:
@corelcaptures wrote:Yes it is a 85mm F2 macro IS STM
Canon certainly does make an RF 85mm f/2 IS STM Macro lens for use on the R-series mirrorless cameras. https://www.bhphotovideo.com/c/product/1547012-REG/canon_rf_85mm_f_2_stm.html (They do not make an 85mm f/2 EF lens for the DSLRs and SLRs. They've made 85mm f/1.2, f/1.4 and f/1.8 for those cameras.)
Therefore I assume the original poster is using the lens on one of the R-series.
That being the case...
A camera and lens can only focus on one thing at a time, at only one distance. If a bunch of things are exactly the same distance, you may see multiple AF points light up indicating they are in focus. But it's merely coincidence.
However, it may not matter if the camera is only focusing on one person. So long as the people you are trying to focus upon are side by side, both the same distance from the camera or very close to it, the plane of focus should be good for both of them. If one or the other is just slightly closer or farther away, "stopping the lens down" to increase depth of field may be necessary to keep both in focus. But with a telephoto lens like 85mm there will be a limit to how much depth of field you can get. If you are photographing a group of people, with multiple rows, you will need greater depth of field.
In case you are unaware, the larger the number, the smaller the lens aperture (this is because an "f-stop" is actually a fraction: "f" divided by "x".) f/2 is a large lens aperture and the largest your lens can do. f/2.8 is one stop smaller, f/4 is two stops and f/5.6 is three stops smaller, while f/8 is four stops smaller and f/11 is five full stops smaller and about the limit before you will start to see loss of fine detail due to diffraction (even though most lenses have even smaller f/16 and f/22 apertures). Depending upon lighting conditions you may need to slow down the shutter speed and/or increase the ISO to compensate for the smaller lens aperture (if using an auto exposure mode the camera may make these changes automatically for you).
85mm is an excellent portrait focal length. What makes it good is that depth of field can be pretty shallow, making backgrounds blur down rather strongly so that subjects can really stand out. You do need some working distance with an 85mm lens... more when there are more than one person. When there is a couple or a small group might be a good time to switch to a 50mm focal length (or a zoom lens that includes that focal length). In part it depends upon the camera. If it's a full frame like R6 or R5, 50mm should work fine. If it's an APS-C camera like R10 or R7, then you may need to go to an even shorter focal length like 35mm or 28mm.
With shorter focal lengths you need to be careful. Get too close to your subject and they well cause exaggerations... big noses, tiny ears. You also need to be careful not to get the people too close to the edge of the image when using a shorter focal length, because there is always some distortion that will make them appear "stretched".
Here is an example where I deliberately used a relatively short focal length (63mm) on a full frame camera and relatively close to the subject, trying to get some humorous exaggeration...
The next two images were shot with 50mm and 85mm lenses respectively, both on APS-C format cameras where they act as short and moderate telephoto lenses (equiv. to approx. 80mm and 135mm on full frame). Both were shot at f/2. Notice the blurred background in the first image and the blurred hand and bottle in the foreground of the second image.
The next two images are group shots (of a sort 😁).... both used an APS-C format camera, the wider first shot uses a zoom set to 24mm, while the second uses the same zoom lens set to 63mm (equiv. to approx. 38mm and 100mm on full frame). Both were shot at f/11 for greater depth of field, to keep the background sharp.
If all this is new to you... how focal length, depth of field, camera format and exposure all work together, I recommend you get Bryan Peterson's book "Understanding Exposure". This is an excellent overview of how cameras and lenses work, filled with a lot of good advice. It is a pretty easy read, though it may take time for some of the concepts to sink in and make sense. If you want to learn to get the best out of your camera and lenses, this book might be a big help!
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
FLICKR & ZENFOLIO
