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09-02-2009, 10:35 AM   #1
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Aperature out of whack

I was hoping to get a little help.

When ever I try slowing down the shutter speed for example 1 second, my aperture always goes way up and the shot comes out all white. I have tried this on all the modes and I always get the same results. At least I think it is the aperture because it is maxed out at +5.

I am using a k-7 (firmware 1.01) and DA 16-45 f/4.

Thanks for any help on this.

09-02-2009, 10:54 AM   #2
pbo
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I think what you are doing is changing EV compensation. EV compensation is changed when you feel the camera's prediction of lighting is biased - so if all shots turn out dark, you turn EV compensation to, say, +1. Then camera uses settings so that it turns out pictures a stop brighter than what was before.
Now, the aperture is another thing. With your lens, the aperture will range from 4 -> 4.5 -> 5.6 -> 6.7 to 8 etc etc (if you're using factory settings and camera's changing settings by half-stop). That's the lower of the two numbers displayed on the top screen, and in the viewfinder it's to the right of the shutter speed.
The rear wheel is *usually* set to change aperture - but of course, that depends on your mode (on factory settings, rear wheel changes aperture on Program and Manual; not sure about other modes) AND it can also be set to change EV compensation in, say, Sv mode.
09-02-2009, 11:03 AM   #3
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Were you hooting in M mode to increase the Tv to 1sec and finding the meter blinking out at +5? There probably isn't an aperture small enough to get a proper exposure in daytime of the scene without blowing it out.

If you really want 1 sec during daytime, you'll need a strong ND filter.
09-02-2009, 11:04 AM   #4
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OK, I meant shooting...

09-02-2009, 11:12 AM   #5
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Sorry but I just want to make sure I am understanding you right Ash.

So I would either need a lens with a smaller aperture than f4 or else I would need to try doing it in the shade outside of direct sunlight?
09-02-2009, 11:47 AM   #6
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The aperture gets smaller as the numbers get bigger. f16 is smaller than f8.
09-02-2009, 11:56 AM   #7
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Johnny, if you are finding this hard to understand, it would be prudent to go back to basics and read up on the fundamentals - the exposure triangle and photographic terminology.

This may explain things better than we can not having seen how you shot those overexposed images.
09-02-2009, 12:07 PM   #8
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Exposure

Why are you using a one second exposure? This is usually reserved for extremely low light levels, or to deliberately cause motion blur.

I don't mean to sound condescending, but it sounds like you don't yet have a firm grasp on the basics of exposure. Please forgive me if I'm wrong. I suggest that you get a copy of "Understanding Exposure" by Bryan Peterson. This is an extremely well-written book, with lots and lots of examples, showing how to achieve a "correct" exposure.

As someone else suggested, it may not be possible to get a one-second exposure in normal daylight, without resorting to neutral density filters. Using the "Sunny 16" rule of thumb, at ISO 100, the normal exposure would be 1/100 at f/16. Since the kit lens goes no smaller than f/32, I believe, you could use a shutter speed no slower than 1/25. To achive a full one second exposure, you would need to be able to set the lens at f/180.

At a given light level, exposure is controlled by three variables: shutter speed, aperture and sensitivity (ISO). As shutter speed goes down, aperture number must go up (smaller opening). As ISO goes up, shutter speed and/or aperture must go up.

For example, at ISO 100, the following shows several equivalent exposures:

1/25 at f/32
1/50 at f/22
1/100 at f/16
1/200 at f/11
1/400 at f/8
1/800 at f/5.6
1/1600 at f/4
1/3200 at f/2.8

As the shutter speed is doubled or halved, the aperture goes up or down by one stop, which doubles or halves the AREA of the aperture opening. In all cases, the equivalent amount of light is allowed to strike the sensor.

Exposure compensation is used to override the exposure combination that the camera chooses. This is necessary, because the camera can't tell which portion of the image you want to be properly exposed and it may guess wrong. In that case, you can dial in the amount of over or under exposure you want. This is used to prevent blown highlights, or to keep detail from being lost in the shadows.

09-02-2009, 12:28 PM   #9
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I agre e with the suggestion to find a good book or web site that explains the basics of exposure. But to address the issues raised here as simply as possible:

When you slow the shutter speed down, the aperture needs to get smaller (higher f-numbers) in order to compensate. But each lens has a limit to how small the aperture can get. The problem isn't that your lens has an f/4 *maximum* aperture; the problem is whatever it's *minimum* aperture is. With ISO turned down as low as it can go (100), on a sunny day you'd need something like f/100 to take a well-exposed picture with a one second shutter speed. No lens I know of comes anywhere near that. The camera is closing down the lens' aperture as far as it can go, but it's not nearly far enough to avoid overexposure.

Bottom line: what you're trying to do is flat out impossible without very strong "neutral density" filter to block most of the light.
09-02-2009, 12:40 PM   #10
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The other thing worth noting is that at a 1 sec shutter speed, you WILL need a tripod unless you have hands that truly are steady as a rock.
09-02-2009, 12:47 PM   #11
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One may think that he has hands as steady as a rock, but really a 1sec exposure is not handholdable - SR or not.
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