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Shortest exposure for Canon XTi/400D when using "Bulb"


alan_rockwood
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Does anyone here know what is the shortest exposure one can make using an external input when the camera is set on "Bulb"?

 

This is kind of backwards from what a lot of people ask, which is how long can you make an exposure.

 

What I have in mind specifically is when using the external connector to control exposure rather than the shutter release button.

 

Thanks.

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Not 100% sure if this is what you're after.

When I use an external intervalometer connected to the bulb port, when I just want an external shutter button to avoid vibration (but no bulb setting) I just set it to manual mode (or which ever mode you prefer to use) and dial the exposure settings I want on the back of the camera.

 

If you do want to use bulb, I guess the minimum exposure is how little you press down the button.

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Thanks for the reply benjaminrussell,

 

To provide a bit more context, in the application I have in mind the camera would be mounted to a modified copy stand. There would be repeated exposures using different shutter speeds. For various reasons I wish to avoid touching the camera during the process, one being the time involved in that process, another being to avoid disturbing the image registration during the process, and a third being to avoid the likelyhood of human error in the manual process.

 

This leads me to look into adjusting the exposure entirely through the external shutter release port. I would generate and send the shutter control signals to the camera from some external device, either a computer or a dedicated circuit.

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If you have a computer w/ the appropriate version of DPP on it, the easiest thing to do may be to shoot tethered.

 

Precise control of exposure length through the external shutter release in B mode may not be possible. While you could easily fab a device which can output the correct signal, the camera's ability to read that signal appropriately may not be adequate... after all, B has never been a precise way to get any finer resolution than 1 sec intervals..

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Marcus Ian, shooting tethered with DPP is an interesting idea. However, I don't think DPP works with the Rebel Xti/400D. (Canon EOS Utility)

 

Regarding using B, is the lack of precision when using less than 1 second due to fundamental limitations of the B setting or to the absences of well-calibrated fingers to operate the B setting?

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I just tried a simple experiment with my Xti. I set the camera on B and flicked the shutter release as quickly as I could with my finger with the camera set to an aperture setting of f/4. Then I found a shutter speed that gave the closest exposure match to the first shot. It turned out to be 1/160 second. I repeated this several times.

 

So, if we assume that the camera would perform similarly using an external shutter release, I am pretty sure I can get the shutter speed down to about 1/160 second when using B, and possibly even faster.

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