I have a nikon d5100 camera with 35mm/f 1.8 lens. I'm not sure what's going wrong with my camera but my photo with larger f-stop numbers is brighter than the photo with smaller f-stop numbers (the ISO and the shutter speed remain the same). Isn't that the photo supposed to be darker on bigger f-stops?

Edit: I'm clearly understood with how aperture works. Just transferred the file into the computer and I have only realized that it was my fault for activating the "AUTO ISO sensitivity control" that messed up the shutter speed and the ISO for the photo I have taken.

Auto ISO sensitivity control in my camera

This is the link that I have referred to: https://www.dummies.com/photography/cameras/nikon-camera/controlling-iso-with-a-nikon-d5100/

My camera is working fine after turning off it. Thank you to everyone who has given an effort in solving my problem.

  • 1
    \$\begingroup\$ 1) What do you mean by "bigger" f-stops? 2) What mode (auto, P, A, S, M etc) do you have your camera in? \$\endgroup\$
    – Philip Kendall
    Sep 20, 2019 at 17:15
  • 2
    \$\begingroup\$ Possible duplicate of What is aperture, and how does it affect my photographs? \$\endgroup\$
    – Rafael
    Sep 20, 2019 at 17:17
  • 1
    \$\begingroup\$ Can you post some examples? \$\endgroup\$
    – mattdm
    Sep 20, 2019 at 17:41
  • \$\begingroup\$ @PhilipKendall OP clearly states "photo with larger f-stop numbers is brighter", which is opposite what is normally expected. \$\endgroup\$
    – xiota
    Sep 20, 2019 at 21:49
  • 1
    \$\begingroup\$ Can you update your question with photo examples, preferably with their metadata intact? \$\endgroup\$
    – BBking
    Sep 20, 2019 at 22:16

3 Answers 3


... my photo with larger f-stop numbers is brighter than the photo with smaller f-stop numbers (the ISO and the shutter speed remain the same).

Since you refer to "f-stop numbers", it appears you know how F-numbers and aperture size are related to each other. You also appear to understand the effect that changing F-numbers should have on the image. When ISO and shutter speed are kept constant, it's normally expected that increasing the F-number reduces exposure, which causes the image to become darker. This is opposite what you describe.

Brighter images taken with smaller aperture sizes could be explained by:

  • Changes in scene lighting.
  • Settings that alter the processing of images, such as Active-D Lighting. The following page has sample images that show how Active-D Lighting affects the brightness of images:

  • Changes to shutter speed and ISO. However, you state they did not change in your case.

  • \$\begingroup\$ +1 for addressing the OP’s question. Changes in the other exposure settings also affect brightness. \$\endgroup\$
    – Lawrence
    Sep 21, 2019 at 0:42
  • \$\begingroup\$ Your answer have just guided me to figure out the possible mistakes that I might have done. Thank you so much sir. \$\endgroup\$
    – Seng Kai
    Sep 21, 2019 at 18:46

I explain it like this: The apeture is like a faucet in a sink. The more you open it, the more water (light) you get. F1.8 is wide open,big hole, lots of light and so a bright photo. f22 is only a tiny hole, so only a trickle of light.... photo is dark.

Then, the shutter setting speeds up or slows down the flow of light... just like the pressure in a water line would increase or decrease the amount of water (or light). So 1/30 of a second doesn't flow as much water (or light) as 1/2 second.

  • \$\begingroup\$ Your answer is pretty useful for beginners like me to enhance my understanding towards the aperture visually. Thank you so much sir. \$\endgroup\$
    – Seng Kai
    Sep 21, 2019 at 18:42

The f-number is the denominator of a fraction.

An f/4 aperture is an opening that has a diameter one-fourth (1/4) the focal length of the lens. An f/8 aperture has an opening that is one-eighth (1/8) the focal length of the lens. One-eighth is smaller than one-fourth.

If we are using a 100mm lens, f/4 means the aperture, as seen through the front of the lens, has a diameter of 25mm because 100mm divided by 25mm equals 4 (100 ÷ 25 = 4). If we change the aperture to f/5.6, the diameter of the entrance pupil (the image of the aperture that is seen through the front of the lens) is reduced to about 17.86mm. Thus a ratio of 0.1786 (1/5.6) is smaller than a ratio of 0.25 (1/4).

So the lowest f-numbers have the widest diameters/largest openings when compared to the highest f-numbers with the smallest/narrowest openings on the same lens.

  • \$\begingroup\$ Although this wasn't what I want, but still an extra knowledge for me to know. Thank you so much sir. \$\endgroup\$
    – Seng Kai
    Sep 21, 2019 at 19:04

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