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The scene is at the distance of say 10 feet. I own Nikon d7200 and a lens of 18-140 mm.

There are three cats here and there (not together), but many of my images focused on one/two cats and not all because the third one was a bit away from the rest two. In other photo, the camera focused only on that isolated cat and not those two.

I need the solution that all three cats are focused, surrounding is focused, and nothing is blurred.

Out of many photos, only a few focused on all the cats and background. But I wanted almost all of them to be like that.

For reference, check this photo. This is one of them what I wanted. But in other photos, all the cats were not at one place. That's why the camera focused only on one/two cats. The background is just a wall, a plain wall. So, no depth of field is to be worried about.

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    \$\begingroup\$ If the cats are all at different distances then depth of field is exactly what you need to be worried about. \$\endgroup\$
    – Michael C
    Commented Jul 5, 2016 at 6:47
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    \$\begingroup\$ Then it is not a focus issue. It is either due to blur caused by subject motion or to poor lens quality that is sharper in one part of the frame or the other. (Assuming you aren't using a tilt/shift perspective control type lens) \$\endgroup\$
    – Michael C
    Commented Jul 5, 2016 at 7:02
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    \$\begingroup\$ This seems to me to be everything to do with depth of field; the wall in your example is not perpendicular to the camera so things are at different distances from the camera, so you need to worry about depth of field. \$\endgroup\$
    – Philip Kendall ♦
    Commented Jul 5, 2016 at 8:00
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    \$\begingroup\$ @MaulikV A camera/lens focusses at a specific distance (5cm, 12ft etc). So if all the cats are "at the same distance" yet "focused on one cat and rest all cats were blurred" then as Michael has already said, it's not focus. You can't focus on one object yet not focus on other objects at the same distance (unless using a TS lens, which you won't be). \$\endgroup\$
    – Steve Ives
    Commented Jul 5, 2016 at 10:13
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    \$\begingroup\$ It would be helpful to see your photo so we know what the issue is we are talking about. \$\endgroup\$
    – Rene
    Commented Jul 5, 2016 at 10:58

2 Answers 2

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What you need is high depth of field. That means the distance range from the camera where subjects are acceptably in focus is longer.

You say depth of field is not the issue since the background is just a wall. The background doesn't matter. It's the min and max distance of all intended subjects from the camera that matters. Clearly this is your problem since you said that you can focus on one cat, but one or more others are not in focus. That means the other cats were at a different distance from the camera than the one you focused on. If you can't arrange the cats to all be the same distance from the camera, then you have to adjust things in the camera so that the acceptable focus distance range covers the whole distance range of the cats. This acceptable focus distance range is exactly what depth of field is.

To get a larger depth of field, use a smaller aperture. You will have to compensate for that with more light, longer exposure time, or higher ISO number. For example, you will have a larger in-focus depth range at f/22 than at f/8. If you go too far with high f-numbers (smaller aperture), diffraction effects start to get noticeable.

Try aperture priority mode at f/22 and see how things look. Start outside with daylight illumination and at the highest ISO your camera can do that gives you the acceptable quality. Now the camera will automatically set the shutter speed to what it needs to be. Depending on the tradeoffs, you might want to use a tripod or monopod to be able to tolerate a slower shutter speed.

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  • \$\begingroup\$ Depth of field is dependent on focal length and will be larger if you keep your lens closer to the wide 18mm end. So you can combine focal length and aperture to achieve the effect you want. Also note that each additional aperture stop means that you need to either double the ISO or double the exposure. @MaulikV \$\endgroup\$
    – MirekE
    Commented Jul 5, 2016 at 14:39
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    \$\begingroup\$ @Mire: Depth of field is larger with a shorter lens, but at the same distance. If you move in or out so that the scene width is the same at the in-focus plane, then you end up with the same depth of field. \$\endgroup\$
    – Olin Lathrop
    Commented Jul 5, 2016 at 15:36
  • \$\begingroup\$ With equal aperture and main subject size the background will appear sharper with the wider lens due to lower magnification. See DOF at constant magnification II at toothwalker.org/optics/dof.html#backgroundblur \$\endgroup\$
    – MirekE
    Commented Jul 5, 2016 at 16:44
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    \$\begingroup\$ "... the background will appear sharper..." and "the background is acceptably sharp enough (to be considered within the DoF)" are two entirely different statements. And in the examples at the link you cite, the camera position is at significantly different distances from the focused subject with each lens. \$\endgroup\$
    – Michael C
    Commented Jul 6, 2016 at 17:51
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Get a tilt lens and use the Scheimpflug Principle. You can even use this technique to keep only one target in focus even if they are on a parallel plane.

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  • \$\begingroup\$ Someone is obviously either never used a tilt lens or is jealous that I have. \$\endgroup\$
    – Matthew Whited
    Commented Jul 6, 2016 at 14:33
  • \$\begingroup\$ That leads to the jealous point. Having the ability to get an off axis plan of focus is not the same as having a wide depth of field. \$\endgroup\$
    – Matthew Whited
    Commented Jul 6, 2016 at 20:07
  • \$\begingroup\$ that can be true... but you can also just set the focus plan along the wall and wait for the cats to stop... In this particular photo it would be rather useless and his "blue" was most probably hand shake from poor lighting. But that doesn't stop the general concept of controlling focus with the angle of the lens from being an option. Could also get a ring flash and close to around f/32 and just cook the kittens with a nice fill flash and fast shutter speed. \$\endgroup\$
    – Matthew Whited
    Commented Jul 6, 2016 at 20:21
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    \$\begingroup\$ Lol. I'm picturing you fiddling with the tilt/shift mechanism and getting everything set up right for where the cats where 30 seconds ago. Meanwhile the cats are running around chasing after dust balls, pouncing on each other, you trying to explain to them how they should stay still. \$\endgroup\$
    – Olin Lathrop
    Commented Jul 13, 2016 at 20:17
  • \$\begingroup\$ On my Rokinon I can adjust it pretty quickly for the tilt/shift the harder part would be focus. \$\endgroup\$
    – Matthew Whited
    Commented Jul 13, 2016 at 20:44

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