Depth of field and lenses relationship

[DM110]

How to get the best image when they both are in focus, but everything behind them is blurry? Are some lenses better for this kind of shots?

What you really want to use is a more telephoto lens and stop it down a bit (to increase the DOF as necessary). As was mentioned above, total DOF is constant with the same subject crop and aperture using different focal lengths, but longer focal lengths will produce a narrower FOV (field of view). Narrower FOV means background objects appear larger within the frame and when those background objects are out of focus, they will appear more blurry as a result. On the flip side, while it's possible to get very small DOF with wide angle lenses, it's often difficult to get the background very blurry because background objects appear small within the frame due to the wide FOV.

As was also mentioned above, the hyperfocal distance increases disproportionately when using more telephoto lenses. A very general way (without going into the optics) to gauge background blur is to divide the hyperfocal distance (dividend) by the subject distance (divisor). The larger the number, the blurrier the background. When the subject distance equals the hyperfocal distance (quotient is 1), the background is "0" blurry - i.e., the background will be completely in focus.

 

[AlanKlein82 21]

What camera are you using?

 

[Tatiana_]

Canon T4i

 

[SDreams]

If I have a Nikon D5200 and I would like to do a lot of Portraiture, what size lens is best to have? Right now, I only have an 18-55mm, I'm not sure what would be better for me to purchase next if I have to choose.....an 18-105mm or 70-200mm range?? Portraiture and landscape are going to be my main subjects.