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When shooting in Bulb mode using my Canon 1200D, I've noticed that the metadata appears to only contain 1" increments for the exposure time. For example, regardless of whether I hold the exposure button for ½ a second or 1 full second, the exposure time listed is always exactly 1". This has led me to wonder:

  • What's the minimum exposure time that can be achieved in bulb mode?
  • Is there a way to retrieve the actual exposure time in either the metadata or elsewhere?
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  • I don't know about a minimum, but a Nikon DSLR has no problem with a precision timer like Stopshot controlling the bulb shutter to be normal exposure durations like 1/50 or 1/200 second. Your report of 1 second seems very unreal. Maybe try a better Exif viewer (like ExiTool), or does the sound of the shutter actually verify those numbers? – WayneF Jan 24 '16 at 4:25
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    @WayneF, It's looking like that's just the reported resolution. Simple exposure tests show that the photo accurately reflects the amount of time the trigger was held. But the reported time in the EXIF metadata is always rounded to the nearest 1" increment. – Andy Jan 24 '16 at 4:37
  • What software or application are you using to access the EXIF metadata? – Michael C Jan 25 '16 at 23:11
  • @MichaelClark - I'm just using iPhoto/Mac Finder. Seems to properly display exposure time for non-bulb mode exposures. – Andy Jan 25 '16 at 23:14
  • There are several different places in the EXIF that Canon records Tv and Av. Some are "set" values and some are "actually used" values. Some are in the "maker notes" section that many applications ignore when displaying EXIF info. I'm currently doing some experimenting to see what my Canon cameras record at various places in the metadata when using a very short Tv in Bulb mode. – Michael C Jan 25 '16 at 23:22
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What's the minimum exposure time that can be achieved in bulb mode?

  1. Technically, the minimum exposure time is probably limited by the speed that a person can press and release the shutter button (or remote shutter release). I assume this is somewhere on the order of 0.1 seconds (1/10 shutter speed) or so. However, this is highly variable and difficult to reproduce shot-to-shot, even for the same person using the same equipment.

  2. Practically, for exposures over a second or two, fractions of a second in exposure don't really matter. For instance, a 2.5 s exposure is only 1/3 stop more exposure than 2 s, and 5.5 s is less than 1/7 stop more exposure than 5 s. When bulb mode is necessary (i.e., when you need exposures longer than 30 seconds), even 1 second resolution is immaterial: 31 seconds is a mere 1/21 stop more exposure than 30 seconds.

Is there a way to retrieve the actual exposure time in either the metadata or elsewhere?

I use Nikon, but the "Exposure time" EXIF data in my long exposure shots shows 0.1 s resolution. Canon cameras round reported bulb exposure time to the nearest second, even if the actual exposure time is a fraction of one second. I have searched Flickr for Canon 1200d photos with long/bulb exposures, but of the few that had "Bulb duration", only integer seconds were shown.

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  • Thanks for the answer - some simple experiments showed that my Canon only has a 1.0" resolution in this regard in the EXIF data, which is a shame. So I think your observations regarding bulb exposures on Flickr is correct too - unfortunately :-( Wanted a Nikon, but budget prevented it. – Andy Jan 24 '16 at 4:35
  • @Andy my answer assumes you're going for long exposure (at least several seconds). Are you using bulb mode under some sort of external control that is doing < 1 second exposures, but can't control the camera's Tv directly? – scottbb♦ Jan 24 '16 at 5:10
  • I'm just controlling directly right now (finger w no fine grained control). Still though I know it's exposing for fractions of a second based on how bright the resulting image is more or less proportional to how long I hold the exposure for (eg not all images displaying 1" have the same brightness). – Andy Jan 25 '16 at 23:17

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