Flash Duration less than sync speed

[will_a.]

<p>Hi there. I was offered a vivitar 5200 for very cheap that I would use with my Bronica SQ.</p>

<p>Would I be able to use this flash even with my shutter speed set at 1/500th? I imagine that the t.1 flash duration is probably around 1/200 at full power. </p>

<p>Anyone know what will happen if you use a flash when the FD is slower than the shutter speed you are syncing it to?</p>

<p>Thanks! </p>

[craig_shearman1]

<p>What makes you think the flash duration is that long? The standard for most flash units (as far as I know) has always been in the ballpark of 1/1000, and then shorter if on auto or lower than full power.<br /><br />I don't have a 5200 but I have Vivitar 283 and 285 flashes and have used them on leaf shuter cameras with the speed at 1/500 and had no problems.</p>

[wayne_f1]

<p>The shutter just has to be open when the flash fires. If the flash were longer duration than the shutter duration, then some light just gets chopped off, less than full exposure passes.</p>

<p>Indoors (meaning, in low and insignificant ambient, so we use flash), the 1/500 second shutter buys you nothing. You could use 1/100 second shutter, and the flash t.1 is still 1/200 or whatever, and in normal situations, the picture indoors won't be different. Neither the 1/500 or the 1/100 second will pass the low ambient (say if assuming ISO 100 and f/8).<br>

<br />Craig, flash durations are normally given as t.5 times, which is duration of the half power points (engineering practice). I think Metz may use t.1. t.1 is the 10% points, and standard t.1 calculation is 3x longer than t.5. Half of the light remains after t.5, so photos are affected by t.1 times.</p>

<p>But the nature of speedlights (cutting flash duration short to reduce power level) means the flash gets chopped off in midstream (faster flash), and other than full power level (not chopped off), the lower levels are faster, and durations are more accurate, maybe more accurate than t.1 times.</p>

 

[will_a.]

<p>Thank you guys for the responses! </p>

<p>Craig, yes I have heard that the vivitar 283 and 285 are real classics. Glad to know that those have worked when syncing at 1/500th. </p>

<p>Wayne, thank you for clarifying about the flash durations. My concern is that I will be shooting skateboarding photos, often in daylight making the 1/500th shutter speed very useful for cutting down ambient light and I would like to have a low amount of motion blur ie. a short flash duration. So correct me if I am wrong, but you are saying that I will loose a little of the flash if shooting at full power at 1/500th (I suppose I would compensate by increasing the aperture or just shooting at 1/2 or 1/4 power to avoid this)? </p>

<p> </p>

[wayne_f1]

<p>Right, in sunlight, the ambient exposure is important too. The continuous light can still blur what the flash already stopped.</p>

<p>Yes, the 1/500 second will just reduce the flash a little. My guess is that the flash duration might be closer to 1/300 t.1, but same concept. You should lose less than the numbers suggest, because all it is cutting off is the low level trailing tail of the flash as it decreases to zero. Cutting that off won't really matter much. A 1/500 shutter is half the duration of a 1/250 flash, but the majority of the flash power is in the first half. You can judge the actual difference of any loss with indoor tests at 1/160, 1/200, 1/250, 1/320, 1/400, etc.</p>

[ian_casement]

<p>The Bronica SQ has a leaf shutter. Whilst it is opening and whilst it is closing it is exposing. You will get no banding, just a reduced from optimal flash output. This is not unusual even with Speedlights and Full and Half power, at full power there is a 'a reduced from optimal flash output' too.</p>

<p>With Speedlights you will be at 1/250s or less. With the Bronica you will be killing ambient a little more. Flash may not be providing more benefit.</p>

<p>The optimal setup would be a faster flash duration.</p>

[rodeo_joe1]

<p>Below is a speedlight flash curve at full output. It's taken from digital storage oscilloscope data of an actual flash discharge capture (Nikon SB-25) and quite typical of this type of portable flash.</p>

<p>You can see that the t0.1 duration is roughly 3mS (1/330th sec). The second, orange, curve is the cumulative exposure over time, and you can see from that that the exposure reaches about 80% of the total light output after 3mS. After 2mS (1/500th sec) the exposure is at 70% of that total. Since a drop in exposure of 10% or so is photographically negligible, the difference between a shutter speed of 1/250th and 1/500th can be disregarded as far as the flash is concerned. However any ambient light will be halved.</p>

<p>FWIW I came across a small Sunpak flash that had an incredibly fast full-power t0.1 discharge of well under 1mS. It's the only one out of around a dozen different flashes I've measured that's markedly faster than the graph shown.</p><div></div>

[will_a.]

<p>Awesome! Thank you Rodeo Joe, this really clears up what I was wondering. So it sounds like it is nothing to worry about shooting with a shutter speed of 1/500th of a second even if the flash duration is about 1/300 of a second. Great to know.</p>

<p>As for that sunpak you found, which model is this? And just how fast is it exactly?</p>

[craig_shearman1]

<p>If you're shooting skateboarding outdoors and 1/500 isn't fast enough to stop the action, the standard solution would be to go to a higher shutter speed. But your Bronica doesn't go higher.<br /><br />If you're trying to use flash to stop the motion, first you need to basically kill the ambient light, which means using the 1/500 shutter speed, a small aperture and slow speed film. You presumably want little if any exposure from the sunlight.<br /><br />But your flash needs to have a shorter duration than 1/500 in order for you to be any better off than you were with just the camera and no flash. Maybe 1/1000 or 1/2000 or shorter. And with the lens stopped down to help kill the sunlight, it also needs to be a powerful flash, probably more so than the Vivitar you're talking about.<br /><br />I don't see how a flash that isn't shorter in duration than your shutter speed buys you anything in terms of stopping the action. And you have to have killed the daylight or the flash exposure will either be irrlevant or show a sharp flash image and a ghost from the ambient.<br /><br />Rodeo/Wayne, am I getting this right?</p>

[rodeo_joe1]

<p>Will, the Sunpak was a feeble little thing - model number something-something 200 - I don't remember exactly. The 200 would seem to indicate a claimed GN of 20 (metres), which means its real GN was probably something like 14 and pretty useless as a main light. I didn't keep the datalog from it, since it fell so far outside the norm. So I can't say from memory exactly how short the t0.1 time was. I was really investigating the difference between "normal" thyristor controlled flash and the so-called HSS extended duration pulsed type.</p>

<p>In case you're wondering, HSS flash offers no advantage whatsoever in combating ambient light. In fact you lose about a stop of power as soon as the flash goes into focal-plane mode. And the flash duration extends to around 7 milliseconds. Presumably to take care of cameras with a slow shutter transit time.</p>

<p>BTW, you can roughly estimate the flash duration of a thyristor-controlled flash at a particular partial power setting by using the cumulative exposure curve. You can see that the curves cross at roughly 50% cumulative exposure, so that would be the time duration for a half-power setting - about 1.5mS. 1/4 power (25%) corresponds to a flash duration of 0.75mS approximately, etc.</p>

[will_a.]

<p>Rodeo Joe, this is all great to know. Since cutting the power the power down gives such short flash durations it sounds sounds like the best way to freeze action in daylight while getting enough power to light up the subject would be to gang a few strobes together at 1/2 or 1/4 power when shooting at say 1/500th of a second or so. </p>

<p>Craig, the idea is that you need fill lighting as well as to stop action. Unless the ambient light is just perfect, it is very difficult to get a skateboarder who is properly exposed without harsh shadows on their face/body. That is why I am not necessarily better off without a flash and just shooting at a fast shutter speed of 1/1000 -1/2000th. </p>

[Rob_the_waste]

<p>Will, I can tell you a bit about all three flashes. The Vivitar 283 and 285 are close together except the 285 lets you adjust the flash intensity by moving the lens in or out for wide angle to telephoto coverage. Funnily enough, I just picked up a 5200 at a camera show today for five bucks. It's just a slightly advanced LCD version of the 285. The flashes as far as I know (and all others for that matter) have an effective duration of around 1/4000 second. I personally never use a shutter speed faster than 1/30 second as I like some ambient light in my pictures. </p>