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Q & A: Moments in time and photographs

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Most recent answer: 01/06/2015
I have a rather offbeat question to ask which you may care to ponder and possible provide an answer to.[But then again there may be no sensible/definitive answer to my question!].Curious! read on. When we take a photograph we capture a moment in time. My question is "How long is that moment in time" that is recorded on the photographic paper. [Im not talking about the shutter speed nor am i talking about its volume, which someone said could be 1 atoms width.] Look at any picture and imagine it, edge on, on a time line. A slice of time has been captured. Is that slice of time 1 second long. Obviously not. If you now devide the 1 second moment by say 100 we have a much shorter moment in time. But even 100th of a second has some time lenght. If we now devide 100th of a second by a factor of 1000x we still have a length value. We could keep subdeviding many times and still end up with a value that has a time lenght how ever small it is. It looks as if the subject in a photogaphic image exists for an almost unimaginably small lenght of time which cannot ultimitly be be defined! Unless you can tell me differently. If your brain has not turned to mush puzzling over this then i welcome any comments you care to make. Best wishes for xmas. Regards. KEN.
- Kenneth Rushforth (age 65)

Dear Kenneth,

You cannot ignore the shutter speed.  Objects you want to photograph emit photons, either by reflection or by self illumination.  There are a finite number of photons per second that strike the film or electronic sensors in your camera.  As you keep reducing the exposure time you will get fewer and fewer photons.  Eventually you don't accumulate enough to  make a decent replication of the object. Too fast a shutter speed and you don't get any!  So a photograph must be an average representation of the image over a finite time: nothing instantaneous.  It that sense a photograph is a time blurred representation of the object.

I'm not sure I understand your philosophical problem about the meaning of time.  Perhaps it is vaguely related to Zeno's paradox  and has to do with expressing a point in space-time as the limit of an infinite sequence.  





(published on 12/12/2014)

Follow-Up #1: limit of short exposures

It seems my answer was wiped off. Let's try it again.Take 10 pictures of a moving object in 1 second and superimpose their frames. You will see a blurry image. Repeat the experiment several times, each time reducing the time form 1 second to 0.1, 0.001, all the way to 0.001. You will see that the superimposed pictures get sharper but also darker--less shutter time, hence, fewer photons reach the film. Each composite frame still contains 10 pictures. Take this to the limit by adding many zeros, 0.000...0001. Now ask your question in terms of this process of shortening the time. Your question will either go away (a non-question) or it will change to another question.Instead of photographs you may think of a segment of a number line from 0.9 to 1.1. Then squeeze this segment to 0.99-1.01, 0.999-1.001 and so on. As you do so the only number that survives this process is 1; all others such as 0.9999 and 1.0001 drop out. Hence, the segment reduces to 1-1. The width of this segment is zero.Similarly, in your example the width of time interval for 1 photograph becomes zero, i.e., no chance for photons to cast an image, i.e., no photo.
- Mehran (age 64)

Mehran- Thanks for this explanation. And welcome back to the site. 

Mike W.

p.s. Rebecca W. followed your advice and fixed the probelm with our question box.

(published on 01/02/2015)

Follow-Up #2: fixed text box

Thank you Rebecca W.
- Mehran (age 64)


(published on 01/06/2015)

Follow-up on this answer.