Slave Flash Oddity

<p>To go along with a small compact camera (with a weak flash), I bought a cheap, equally compact, slave flash that is easy to pocket and take with me on travel or to parties. Some months ago, I received useful advice on how to use this little flash, but in working with it discovered an oddity. In auto mode (not TTL) there are three power settings.</p>

<p>A guide on the back of the flash offers ISO/f-stop combinations for each power setting. So, e.g., on A3 (the highest setting), there is an ISO 200/f7 combination. In one respect, these combinations make sense, I suppose, even without a distance measure, in that so long as your subject is within the slave's range, the meter will set the flash duration at any given power setting under the assumption that the camera is set at the designated ISO/f-stop combination. But it occurs to me that the table is insufficiently informative in that it offers no sense of available range at wider openings than indicated on the chart. Wouldn't it be helpful to have a chart assuming highest power and, say, ISO 400, with maximum distance at various aperture settings? That would be faster tan a GN calculation. Just a thought.</p>

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<p>"Wouldn't it be helpful to have a chart assuming highest power and, say, ISO 400, with maximum distance at various aperture settings?"</p>

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<p>So make yourself one!</p>

<p>The maths isn't hard. For every doubling of ISO speed you multiply by 1.4. Going the other way and halving the ISO you simply divide by 1.4. <strong>IF</strong> you try to apply the same to the distance scale in Auto mode, it won't work, because the flash will simply overexpose if you use an F-stop wider than that given. <strong>But</strong> if you change to manual power, then you can make a distance chart. For every F-stop wider, or doubling of ISO you can multiply the distance by 1.4, and conversely halving the ISO or stopping down one stop means you have to divide the distance by 1.4 (or multiply by 0.7).</p>

<p>Using your example of ISO 200 and f/7: With 400 ISO you'd use an F-stop of f/10, but the maximum useable distance wouldn't be any greater, because the Auto-Aperture settings only allow for a fixed aperture. You'd have to go back to manual power settings and use the old GN calculations to get the flexibility that you seem to want.</p>

<p>Creating such a table in Excel would be easy, and transferable to a mobile device such as a smartphone.</p>

<p>IDK what drove the designers of your flash - Metz' did a good job with their manual power limiter calculator combo on top of the 60CT4, but that flash is far from pocketable.... Aren't ergonomics frequently sacrificed for size's sake?</p>

<p>Thanks. In response to Joe, what you propose is a chart based on GN, and one is provided. What I was suggesting was something that could be done more quickly when there is concern that the subject is too far away properly to expose. In such a case, I'd open my lens as wide as possible and maximize the flash's power and it would be helpful if a quick guide told me how far I can expose with that flash at various maximum apertures. But you are right that I could use the GN info to create such a chart. I was just curious why the flash manufacturer didn't include one, more useful, it seems to me on such a small and weak flash than info on variable auto power settings. That said, yes, I agree with Jochen that this tiny flash provides plenty of info for its size; just questioning what info.</p>

<p>Guide Number divided by F-Number = (maximum) flash distance. That's how Guide Numbers work. So if the maker of the flash has printed a GN table, then I don't see what other information they needed to provide you with.</p>