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Can 'auto ISO' be used when using a flash?
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<blockquote data-quote="WayneF" data-source="post: 280659" data-attributes="member: 12496"><p>ISO 200 seems unexpected. I would have expected higher. Settings could affect that. What were your Auto ISO settings for Minimum ISO and for Maximum ISO? (Normally) it cannot go below minimum or above maximum.</p><p></p><p>But... the TTL flash is still automatic metered exposure, regardless of camera settings like shutter speed or ISO. TTL is metered, and the design is that the TTL flash power level is set to be what it needs to be, to be correct for whatever situation. It is not always precise, but if we want to pursue it, we will need more information about why the subject was blown out. A sample picture of the problem would help, along with either Exif or details of ISO, shutter, aperture, distance, any special conditions, etc. Was it direct flash or bounce? Direct flash is sometimes blown out a little. We control what the TTL automation does with Flash Compensation, specifying either +EV or -EV changes to the results we see.</p><p></p><p></p><p></p><p>If bounce flash, the SB-400 (a lower powered flash) may need ISO 800 if like f/4 under a ten foot ceiling. For direct flash though, that seems higher than necessary, ISO 200 is probably fine.</p><p></p><p></p><p></p><p>There are several ifs and buts about flash. Making up example numbers, but for example, if with the flash turned off, often the indoor scene typically meters say f/5.6 at 1/2 second. You reach up and turn the flash on, and it changes to f/5.6 at 1/60 second (in camera A or P mode). This 1/60 is NOT sufficient exposure for the ambient, which we just said needed 1/2 second. The 1/60 is Nikons Minimum Shutter Speed With Flash... if using flash, we have no need that it be 1/2 second. But that makes the ambient be about five stops underexposed (we are after all using flash instead).</p><p></p><p>So... in that case - any camera shake caused by the "slow" 1/60 second is too dark to be visible.. it is "don't care". Instead the flash duration is vastly faster, and will stop the motion (of camera shake, or from the moving subject too). Hot shoe flashes are called speedlights for this reason.</p><p></p><p></p><p></p><p>It is common to use camera Manual mode M with flash indoors. Obviously, if it meters 1/2 second without flash, the ambient is not a consideration any more. And shutter speed does NOT affect flash exposure at all. But instead of always using 1/60 second, we can choose another shutter speed, faster to block all ambient (typically orange from incandescent), or slower to allow some of the ambient in. Our choice in camera M mode. The flash is still fully automatic TTL mode, regardless.</p></blockquote><p></p>
[QUOTE="WayneF, post: 280659, member: 12496"] ISO 200 seems unexpected. I would have expected higher. Settings could affect that. What were your Auto ISO settings for Minimum ISO and for Maximum ISO? (Normally) it cannot go below minimum or above maximum. But... the TTL flash is still automatic metered exposure, regardless of camera settings like shutter speed or ISO. TTL is metered, and the design is that the TTL flash power level is set to be what it needs to be, to be correct for whatever situation. It is not always precise, but if we want to pursue it, we will need more information about why the subject was blown out. A sample picture of the problem would help, along with either Exif or details of ISO, shutter, aperture, distance, any special conditions, etc. Was it direct flash or bounce? Direct flash is sometimes blown out a little. We control what the TTL automation does with Flash Compensation, specifying either +EV or -EV changes to the results we see. If bounce flash, the SB-400 (a lower powered flash) may need ISO 800 if like f/4 under a ten foot ceiling. For direct flash though, that seems higher than necessary, ISO 200 is probably fine. There are several ifs and buts about flash. Making up example numbers, but for example, if with the flash turned off, often the indoor scene typically meters say f/5.6 at 1/2 second. You reach up and turn the flash on, and it changes to f/5.6 at 1/60 second (in camera A or P mode). This 1/60 is NOT sufficient exposure for the ambient, which we just said needed 1/2 second. The 1/60 is Nikons Minimum Shutter Speed With Flash... if using flash, we have no need that it be 1/2 second. But that makes the ambient be about five stops underexposed (we are after all using flash instead). So... in that case - any camera shake caused by the "slow" 1/60 second is too dark to be visible.. it is "don't care". Instead the flash duration is vastly faster, and will stop the motion (of camera shake, or from the moving subject too). Hot shoe flashes are called speedlights for this reason. It is common to use camera Manual mode M with flash indoors. Obviously, if it meters 1/2 second without flash, the ambient is not a consideration any more. And shutter speed does NOT affect flash exposure at all. But instead of always using 1/60 second, we can choose another shutter speed, faster to block all ambient (typically orange from incandescent), or slower to allow some of the ambient in. Our choice in camera M mode. The flash is still fully automatic TTL mode, regardless. [/QUOTE]
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