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I have a Nikon D60 camera here with a Nikkor 35 mm 1:1.8G lens. I don't have any experience with any other digital SLR, so excuse the beginner question.

When using aperture priority mode, a narrower aperture gives a very noticeably darker pictures. The picture becomes so dark that I usually feel the need to increase the exposure compensation setting when using a narrow aperture.

I would expect the automatic shutter speed adjustment to give pictures with approximately the same brightness, regardless of what aperture setting is used.

Is the behaviour I see usual? Or does it indicate a problem with the camera's metering? If it is usual, is there a technical reason for it (e.g. some limitation in how the metering is done)?

Here are two test photos to demonstrate what I mean: one and two. The first one was shot with an aperture setting of 3.5, the second one with 18 (you can see this in the EXIF info). The camera did not reach the fastest possible speed during this test and the metering was set to "matrix" to minimize the effect of me moving my hand between the two shots.

Some updates: The D60 continues to give noticeably incorrect exposures with this 35 mm lens when stopped down. It works fine with a 18-55 mm f/3.5-5.6 lens though. This would suggest that there's a problem with the lens. However, a D7100 gives consistent exposures with the same 35 mm lens regardless of aperture.

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    \$\begingroup\$ In aperture priority I would expect the shutter speed to automatically change to balance out the selected aperture, giving an equally exposed photograph. Was your ISO fixed? Or perhaps there was no exact equivalent exposure that it could get. That said the brightness change is quite a lot, so I am wondering if you had the AF mode to full all-point AF, and it happened on the 2nd shot to AF on a different part of the picture, and since the metering is linked to the AF point (I think), that explains the difference? Perhaps try again with fixed ISO and a fixed AF Point that you know won't move... \$\endgroup\$
    – Mike
    Commented Jun 11, 2012 at 13:48
  • \$\begingroup\$ @Mike The ISO was fixed (it's always fixed in A mode on this camera). The shutter speed is adjusted by the camera, but it does not balance out the aperture change perfectly: I consistently get a darker shot when the aperture is narrow. In fact, the owner of this camera (it's not mine) mistakenly believed the the aperture is used for adjusting brightness in A mode. I did not know that the AF point can have an effect, so I'll try t fix it as you suggest, but since the brightness of the result is consistently linked to the aperture, I don't expect it'll make a difference. \$\endgroup\$
    – Szabolcs
    Commented Jun 11, 2012 at 13:52
  • \$\begingroup\$ @Mike I played a little more: I fixed the AF, I made sure the camera wouldn't move between shots and I tried different metering modes (spot & matrix). A narrower aperture always gives a darker picture. Meanwhile someone in chat said they can't reproduce this behaviour, so it must be specific to this camera I have here. I am now wondering if every Nikon D60 has this problem (with a similar lens), or if something got broken in the metering of the camera. \$\endgroup\$
    – Szabolcs
    Commented Jun 11, 2012 at 14:07
  • \$\begingroup\$ The photos you post don't show much (any?) difference in depth of field. Can you try shooting something else -- perhaps a ruler, pointed towards the camera, up close, so that we can see the plane of focus? I'm suspicious the aperture of the lens isn't actually changing... \$\endgroup\$
    – Dan Wolfgang
    Commented Jun 11, 2012 at 15:06
  • \$\begingroup\$ @Dan Do you mean that the lens may be faulty and the aperture is not being changed properly? This is not the case for the following reasons: 1. I can see that the aperture is narrowed during a shot when looking into the lens 2. if that were the case, the photo with the slower speed should be brighter, but in fact it's darker. 3. the change in depth of field is clearly visible when shooting with different apertures (i.e. what you asked about). These test shots were just made off the terrace, and focused on infinity. \$\endgroup\$
    – Szabolcs
    Commented Jun 11, 2012 at 15:46

5 Answers 5

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Ok time to cut through a little of the confusion:

  • Technically there should be no difference in exposure when using a smaller aperture in one of the automatic modes as the camera should vary the other parameters to compensate. You might see a difference in the extreme corners due to vignetting at wide apertures, but this would make the small aperture shot brighter.

  • In this case shutter speed decreased in the small aperture shot, meaning in this case metering is not [entirely] to blame. There was a 1/3 stop discrepancy between shots however.

Lets dig into the details a little...

The recorded parameters for the two shots were 

1/1250s f/3.5

and

1/60s f/18

ISO was 100 for both. Exposure is proportional to shutter time over f-number squared. This gives a 1/3 stop disparity in the camera settings (this is probably a result of the camera's meter, however I'd be willing to forgive this minor variation as the composition did change a bit).

However if you look at the images, taking a reading from the highlighted side of the building bottom centre gives:

RGB = [134, 138, 135]

and

RGB = [74, 73, 72]

assuming a roughly linear tonecurve (unless you shot RAW we can't assume otherwise) this gives a 0.9 stop difference. So clearly there is something else going on here.

f/18 isn't exactly a third of a stop down from f/16, it's just rounded to 18 for convenience. In any case we don't know how accurately the camera can control the aperture when it's that small. Likewise you would expect some variation in shutter speed. As the shutter gets worn the curtains can get out of sync, giving you considerable variation, especially at high speeds.

If we say the actual settings used were 

1/1100s f/3.4
1/65s f/19

Then suddenly we get a 0.9 stop difference in the expected exposures. There other factors that could be involved

  • Slight haze passing in front of the sun can drop the exposure slightly whilst not being noticeable to the human eye.

  • Nonlinear tonecurves and image processing in camera to produce the JPEG

Normally these things cancel out, but if they all line up one way you can get sizeable swings in exposure.

The lesson to bring from this is that it's probably normal, if it happens consistently it may well be something out of calibration, but I wouldn't worry about it, the camera's meter is not infallible, a better approach [] with digital is just to check the histogram after each shot.

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  • \$\begingroup\$ Thanks for the analysis, Matt! It explain why the problem might be caused by the lens (possible problem with aperture control). I found a number of forum threads mentioning that this may be due to a problematic lens (see my last comment on the main question). BTW I used JPEG when shooting these (I wanted to make sure that the EXIF data is preserved), but I get the same effect when shooting RAW. I'll accept this answer in a couple of days if nothing else comes in. \$\endgroup\$
    – Szabolcs
    Commented Jun 12, 2012 at 19:09
  • \$\begingroup\$ At the time when I posted the question, I did not have the possibility to try the lens on another camera or to try another lens on the same camera. Since then I could do that. It seems that the problem is only present with this lens-camera combination. The same lens works fine on another camera and the same camera doesn't underexpose with another lens. \$\endgroup\$
    – Szabolcs
    Commented Jul 27, 2013 at 19:11
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The ISO for both pictures is the same: 100
F-stop are f/3.5 and f/18: i.e. 4 2/3 stops
shutter speed is 1/1250 and 1/60: i.e 4 1/3 of a stop.
So the exposure value for the two pictures are not the same...
DSLR's calculate exposure using maximum aperture may be that is why you have a darker picture when stopping down the aperture.

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    \$\begingroup\$ When I use small apertures, I almost always adjust the Exposure Compensation. Most of the time, my camera's metering itself suggests that a shot it under-exposed when using small apertures. \$\endgroup\$
    – publicRavi
    Commented Jun 11, 2012 at 14:18
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Is it usual that a narrow aperture gives a darker picture in aperture priority mode?

No, it is not usual.

does it indicate a problem with the camera's metering?

It might, or there may be a problem with the specific lens. You can find out by trying a different lens on the D60 and also trying the 35mm on a different camera. If you don't have a friend with a Nikon DSLR camera, you might ask a friendly camera store.

is there a technical reason for it (e.g. some limitation in how the metering is done)?

The scene in your sample shots could be a very bright day requiring fast shutter and small apertures at low ISO. A neutral density filter could help by reducing the amount of light to a level where the mid point of the available speed/aperture/sensitivity is used. Try taking a pair of shots somewhere darker and see if the same problem persists.

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What METERING MODE are you using? Cameras like the 60D usually offer a variety of metering modes, which affect how a scene is processed in order to determine a proper exposure. Evaluative/Matrix metering should produce a correct exposure for both the f/3.5 and f/18 shot. If you are using a center weighted, partial, or spot metering mode, or some form of AF-point linked metering mode, then you could indeed encounter differing exposures when using a semi-automatic camera mode like aperture priority.

Find and set your metering mode to evaluative/matrix, and see if that fixes your problem. If not, then there might be an issue with the hardware. The D60 is getting pretty dated now, and its metering hardware may not be as capable and exact as in more modern DSLR gear. I would suspect, however, that you have simply selected a different metering mode...probably an AF-point linked spot meter mode. Changing back to Matrix should fix the problem.

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  • \$\begingroup\$ The result is the same regardless of the metering mode I use. But for the test shots I linked to I did use matrix metering mode (actually I mentioned this in the question). \$\endgroup\$
    – Szabolcs
    Commented Jun 12, 2012 at 6:46
  • \$\begingroup\$ If you look at the EXIF there is a 20% percent difference in exposure, which could be the result of metering, however the images posted show a much greater brightness disparity. \$\endgroup\$
    – Matt Grum
    Commented Jun 12, 2012 at 10:55
  • \$\begingroup\$ @MattGrum: That could definitely be the result of metering, if its based on spot metering. I've had more than 20% differences when I used to use spot metering for BIF photography. In high FPS mode, shots where the bird was directly under the metered area would have one exposure, and shots where the bird had moved out of the metered area could be radically different, either much darker or much lighter. So its certainly not impossible that the problem is due to metering. Szabolcs has noted that metering mode is evaluative already, so that is problably not the problem. \$\endgroup\$
    – jrista
    Commented Jun 12, 2012 at 16:53
  • \$\begingroup\$ @jrista I'm not sure I understand what you're saying, the metered exposure was a third of a stop different, but the images differ in brightness by a whole stop, so even if the OP shot in manual the stopped down image would be two thirds of a stop darker that reciprocity would suggest. That's why I'm saying the problem isn't with metering. \$\endgroup\$
    – Matt Grum
    Commented Jun 13, 2012 at 13:35
  • \$\begingroup\$ @MattGrum: Ah, sorry. Didn't realize you had calculated the actual difference as a full stop. You're explanation above sounds solid. :) \$\endgroup\$
    – jrista
    Commented Jun 13, 2012 at 17:36
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I an not familiar with the Nikon D60, but...

Perhaps the camera is reaching a minimum shutter speed, and will not lower the speed below a certain level?

This may be be intended to prevent camera shake?

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