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Sq-a and setting iso


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<p>I'm a little ashamed to ask this question. But i have a Brinca Sq-a loaded with Ilford fp4 @ 125iso.</p>

<p>The Sq-a 120mm back has 1/3 increment markings between the 100 and 200 iso speed settings. Should a 125 iso film as i'm using just be set to the first increment past 100?</p>

<p>Sry about this terrible question btw!</p>


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<p>The "easy" way to remember what 1/3rd stop shutter speed or ISO increments are, is that the multiplier is the cube root of 2. Windows calculator tells me this is 1.2599, or 1.26 near enough.<br>

So the sequence runs:<br>

50 ISO x 1.26 = 63 (~64 ISO)<br>

64 x 1.26 = 80.64 (~80 ISO)<br>

80 x 1.26 = 100.8 (~100 ISO)<br>

100 x 1.26 = 126 (~125 ISO)<br>

126 x 1.26 = 159 (~160 ISO)<br>

160 x 1.26 = 200<br>

200 x 1.26 = 252 (~250 ISO)<br>

250 x 1.26 = 315 (~320 ISO)<br>

etc. And you just need to double these figures to carry on the sequence from here.</p>


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<p>The ASA/ISO film speed dial on the film back can automatically couple to a finder which has a built in exposure meter. ...such as a metered prism finder or metered magnifying hood. With a flip up hood, the dial is simply used as a reminder of what speed is in the film holder. This is useful if you have more than one back, and have different film speeds in them.</p>
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