Traditionally full f stops reflect the aperature opening that is needed to half (or double) the amount of light passing to the sensor. As we progress up the f stops 0.5- 128 we decrease the light by half with each smaller opening.
<table style="text-align: center;" class="wikitable"]
<tbody>
<tr bgcolor="#ccffcd"]
<td>


0.5
</td>
<td>0.7</td>
<td>1.0</td>
<td>1.4</td>
<td>2</td>
<td>2.8</td>
<td>4</td>
<td>5.6</td>
<td>8</td>
<td>11</td>
<td>16</td>
<td>22</td>
<td>32</td>
<td>45</td>
<td>64</td>
<td>90</td>
<td>128</td>
</tr>
</tbody>
</table>


So 1.4 - 2.2 is a 'stop' and 16-22 is a 'stop' but each stop does not representthe same


amount of light being blocked.


We also use the term 'stop' to refer to a change in speed settings


1 sec 1/2 1/4 1/8 1/16 1/32 1/64 1/128 1/256 1/512


likewise were refer to changing the speed setting from 1/4-1/8 as a 'stop' decrease


and also a change from 1/128 - 1/256 as a stop decrease.


Each will decrease the amoung of light passing through to the sensor.


The 1/128-1/256 represnts much less light stopped that 1/2- 1/4.


Just like the aperature stops the speed stops decreae the light by half (or double)


but this is where the simularity ends.


Certainly each stop is not stopping the same amoung of light.


This leads usalso to the realizationthat time stops and aperature stops can not be directly


compared. Changing and aperature by one stop has no direct translation to changing


speed by one stop.


To make this also more confusing as our camera are marked in partial f stops and partial


timechanges.


So why all this:


Comments are beign made like:


A stop is a stop


or


IS improves hand held by 3 stops (stops of speed not aperature)


do we cosider this true over the entire stop range ie 1 sec exposure is improved by 3 stops


as well as a 1/60 exposure improved by 3 stops. NO


A stop is not a stop. It is relative.



I think we throw the term stop around a little too loosely lately.


Comments?