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I have calculated the depth of field for my Sony RX100M3. I have done so numerous times for all three parameters: focal length, subject distance and apperture.

I noticed that for sufficiently large subject distances (~50-100 m) and keeping the equivalent focal length fixed at 24mm, the depth of field is relatively not so much affected by aperture. The bandwith of aperture for the Sony RX100M3 is f/1.8 to f/11.

Is it true that the aperture does not affect depth of field that much for large subject distances?

At what 'cost' can we let the aperture wide open other then that subject of interest appear smaller?

I am new to photography and I would love if someone could enlighten me with this question.

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    \$\begingroup\$ Keep in mind that depth of field is arbitrary until one selects a display size and viewing distance. It's the area where things are acceptably sharp. There is only one actual distance that is most in focus. There is no distinct line between "sharp" and "blurry" at the "edge" of the DoF. Things gradually get blurrier the farther they are from the focus distance. At some point that blur becomes enough to be noticeable to our eyes. For the same photograph, changing the display size or viewing distance also changes the perceived DoF. \$\endgroup\$
    – Michael C
    Commented Feb 18, 2020 at 16:36
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    \$\begingroup\$ Most DoF charts/formulae assume a display size of around 8x10 or 8x12 inches viewed from a distance of about 10-12". Display the same photo at 16x20 and view it from 12" and the DoF will be shallower by roughly half. \$\endgroup\$
    – Michael C
    Commented Feb 18, 2020 at 16:39
  • \$\begingroup\$ Thanks for the insightful comments. I agree that the perceived DoF highly depends on the size it is printed or shown and the distance at which it is viewed from. \$\endgroup\$
    – Nadia Merquez
    Commented Feb 18, 2020 at 17:19
  • \$\begingroup\$ Comment: If I understand your statement " other then that subject of interest appear smaller?" correctly then you may be confused to some effects of aperture setting. Aperture essentially does NOT alter the size of the subject of interest or the subject. Focal length does, of course. \$\endgroup\$
    – Russell McMahon
    Commented Feb 19, 2020 at 0:22
  • \$\begingroup\$ The hyperfocal distance for a given lens that has an aperture that is wide open is relatively large (compared to a smaller aperture) . Hence, I referred 'cost' to a large subject distance. And trivially, a large subject distance makes the subject appear smaller. \$\endgroup\$
    – Nadia Merquez
    Commented Feb 19, 2020 at 21:34

2 Answers 2

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That observation is true.

The nearer to the lens, the smaller the depth of field.

If you use an online DoF calculator like e.g. https://www.dofmaster.com/dofjs.html you can easily see this. 

Example: full frame, 50mm f1.4
at  1m -> DoF appr  0.02m
at  3m -> DoF appr  0.19m
at 10m -> DoF appr  2.16m
at 50m -> DoF appr 75.40m 
at 95m -> DoF infinite (behind)

So, once you have reached a certain distance, the aperture will not give you more DoF behind the focal point, but it might influence the near limit where the DoF starts. You can use this to your advantage to calculate the best DoF for landscape photography.

You should also be aware in this context, that the aperture has an effect on the sharpness. There is no fixed aperture of the best performance of a lens, so you need to test that for each lens. Many lenses have their peak performance around f3.2 to f5.6, but your mileage may vary greatly. If you chose a very small aperture like beyond f16, you start getting refraction problems, which decreases lens performance. So it might be worth checking for the sweet spot of each lens. Or in your case, the sweet spot of the fixed lens.

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    \$\begingroup\$ I would like to add that aperture does affect sharpness, so if the DOF is of no concern it is still wise to go with an ap. of +/- 2 stops from wide open \$\endgroup\$
    – timvrhn
    Commented Feb 18, 2020 at 13:06
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    \$\begingroup\$ Thanks for answering the question. It cleared the confusion. However, can the subject distance of the focus area be measured and given by the camera? Or should one provide a rough estimate himself/herself? \$\endgroup\$
    – Nadia Merquez
    Commented Feb 18, 2020 at 13:56
  • \$\begingroup\$ @NadiaMerquez Yes, most cams either have the option to display the distance, or if the lens has a scale you can roughly see it there. Some mirrorless cams also show you a graphical representation of the distance plus DoF. My old Fuji XT-1 could do that. The Sony a7 III, I currently use, can't. \$\endgroup\$
    – Kai Mattern
    Commented Feb 18, 2020 at 15:46
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    \$\begingroup\$ @timvrhn That's highly dependent upon the lens in question. As a general rule, it's more true of lower end wide-angle to normal lenses, and less true of higher end telephoto lenses. Canon's Super Telephoto series, for example, are almost all universally sharpest wide open, because their designers have optimized them that way. \$\endgroup\$
    – Michael C
    Commented Feb 18, 2020 at 16:31
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    \$\begingroup\$ Thanks for the comments and I marked the answer as the correct. Unfortunately, I believe that the Sony RX100M3 is not capable to depict the focus distance on the display. So, I'll have to do some guessing with respect to focus distances. \$\endgroup\$
    – Nadia Merquez
    Commented Feb 18, 2020 at 17:15
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Reading about the concept "Circles of Confusion" may help you resolve the questions and thoughts you are asking about.

You'll also see that the DOF for a lens and viewing and crop is identical- the DOF for the same subjective size cropped from a 24mm lens is the same as the DOF for a subjective crop same size subject of a 100mm lens. Popular Photography did a wonderfully illustrated issue with that concept decades ago, but I can't find the issue.

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