Why does the lower f-stop in my camera makes the photo darker?

Question

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.

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.

Possible duplicate of What is aperture, and how does it affect my photographs? — Rafael, Sep 20 '19 at 17:17
@PhilipKendall OP clearly states "photo with larger f-stop numbers is brighter", which is opposite what is normally expected. — xiota, Sep 20 '19 at 21:49
Can you update your question with photo examples, preferably with their metadata intact? — BBking, Sep 20 '19 at 22:16
@Seng Kai You say the ISO and shutter speed remain the same but you don’t mention the subject and lighting. Do they also remain the same? — Mike Sowsun, Sep 21 '19 at 10:07
Possible duplicate of How can i shoot in aperture priority with auto ISO? — scottbb, Sep 23 '19 at 22:56

xiota · Accepted Answer · 2019-09-21T07:51:36.610

... 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:
- Nikonites: Active D-Lighting For the D5100
Changes to shutter speed and ISO. However, you state they did not change in your case.

+1 for addressing the OP’s question. Changes in the other exposure settings also affect brightness. — Lawrence, Sep 21 '19 at 00:42
Your answer have just guided me to figure out the possible mistakes that I might have done. Thank you so much sir. — Seng Kai, Sep 21 '19 at 18:46

score 0 · Answer 2 · answered Sep 21 '19 at 00:13

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.

Your answer is pretty useful for beginners like me to enhance my understanding towards the aperture visually. Thank you so much sir. — Seng Kai, Sep 21 '19 at 18:42

score -2 · Answer 3 · answered Sep 20 '19 at 18:50

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.

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

Why does the lower f-stop in my camera makes the photo darker?

3 Answers3