Calculating number of stops


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Jan 31, 2007
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#1
Hi

I read somewhere in a magazine. The author set camera to AP mode and had an exposure of 1/2s. He moved 5 stops and achieved 1/30s. I was trying to figure out how to calculate number of stops. My calculations was obviously wrong as I thought 1/30s was 4 stops, not 5.
 

attap seed

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Feb 16, 2006
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#2
1/2, 1/4, 1/8, 1/15, 1/30

its 4 stops.




but i dun understand the whole concept.

set to AP, then underexpose by 5 stops?

but then, in AperturePriority mode, u cant underexpose. by adjusting the aperture, the shutter speed automatically changes to accomodate it (the aperture) to achieve the rite exposure.

in Av, u can compensate exposure by the ExposureCompensation dial. but i doubt 5 stop over/under is possible. my 30D cant.

which magazine are u reading?
 

Trapper

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Sep 25, 2008
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#3
He didn't say the author underexposed, merely moved 5 (it should be 4 by my count too) stops. Moving from f/11 and 1/2s to f/2.8 and 1/30s for example will give him the same exposure settings.
 

gymak90

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Jan 5, 2008
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#5
What magazine is that? It's clearly 4 stops and not 5.

To attap seed: No the magazine didn't say it was underexposed.
 

attap seed

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#7
oic. i mis-understood.

cus, i feel that its redundant to say, set to Av mode, had a exposure of 1/2 sec, then adjust to 1/30 sec.

cus, if i set to Av, if i need f11, i jus set to f11. i wun say, from 2.8, i adjust 4 stops to f11.
 

Trapper

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#8
I'm guessing it's probably an article to illustrate how to get a more handhold-able shutter speed while keeping the same exposure, in which case (error in stop calculation aside) it illustrates the point pretty well. :dunno:
 

Jan 31, 2007
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#9
Hi

Thanks for clarifying.

Let me clarify the situation it was used. Sorry for causing the confusion as my question was phrased to get the answer and not whats the situation.

It was basically about setting to AP and do spot metering of multiple points before changing to manual mode and shoot. :)
 

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