Would Like To Verify Exposure Duration

Started 4 months ago | Questions thread
xpatUSA
xpatUSA Forum Pro • Posts: 19,064
Re: A simple WWW app

CharlesPhillips wrote:

ProfHankD wrote:

CharlesPhillips wrote:

All -

After solving several other difficult questions, now another one comes up. I have a Nikon D200 and use it to take photos of satellites, using mostly 10 second exposures. But it appears that the exposures are not exactly 10 seconds.

I am trying to think of way to measure the duration, I'd like to know to the tenth of a second. I think that the exposures are a little long.

I am cross posting to the Nikon discussions.

Easy check: photograph a changing computer display. Most computer displays refresh at least 24 times a second, usually 30 or 60, so you just need a program that simply outputs a character in a new position every 1/10 second. Better still, here's a javascript page I just threw together to do it for you:

http://aggregate.org/DIT/shutspeed.html

Just load that page, photograph the screen, count how many # images you see, and divide by 10 to get the number of seconds for the exposure. A complete line is 1 second. It might work better if you invert the text and background colors for white text on a black background.

That has been very illuminating (photography humor). A "5" second exposure is 2.5 seconds long! A "10" second exposure is about 5.1 seconds long!!

So I can just cut the displayed exposure time in about half.

I am gonna try to improve my timing technique but this has to be pretty close.

Late to the thread but some cameras put the actual exposure time in the image meta-data as well as the rounded fraction.

For example, Sigma DP2:

BEGIN: CAMF matrix meta data (CaptureExpTime)
float [1]
x: D0
76120 <---
END: CAMF matrix meta data

BEGIN: CAMF matrix meta data (CaptureShutter)
float [1]
x: D0
56116 <---
END: CAMF matrix meta data

They look like micro-seconds - the displayed value is 1/15 sec, listed as a string elsewhere in the meta-data.

Don't ask me why ExpTime (1/14.899) and Shutter (1/17.820) are different ...

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