Not getting full flash power at 1/500th with Copal shutters, why?

[john_jovic]

<p>I've been testing some strobes with a Rodenstock large format lens with a Copal shutter (the same shutter you

'd find in a leaf shutter lens). The shutter goes to 1/500th and I intended using it with some battery strobes, Me

tz, Canon and Nikon, for outdoor use. My problem, or question, is that I don't get full flash power at 1/500th regardless

of the strobes I use. In other words, when I use the strobes at full power I lose about 1/2 a stop at 1/500th comp

ared to 1/250th and slower shutter speeds. This has happened with the 3 stobes I've tested but to slightly diffe

rent degrees and mainly at full power but to a slig

htly lower degree at 1/2 power. The problem dissapears completely at 1/4 power on the strobes so the light output is ident

ical at 1/500th, 1250th and lower.<br>

All I can think of is that the flash duration is too long with these battery strobes at full power but short enou

gh at lower power that they work at 1/500th.<br>

Am I on the right track and how do I know how to avoid this i

ssue in the

future as I'

m interested in

[cabbiinc]

<p>The flashes power is controlled by the duration, but 1/500th shouldn't be too short. I'd suspect your triggering system. If your using wireless triggers what kind are they? Do you have fresh batteries in everything (flashes and triggers)? If you have wireless triggers with antennas, are the antennas up? Away from interference? Are you shooting at any great distances?</p>

<p>The fact that 1/4 and lower is the same at the different shutter speeds makes me think that your flashes are just triggering too late, and 1/4 and lower is quick enough for a proper exposure.</p>

[john_jovic]

<p>Hi Dan.<br>

Flashes are connected directly to the PC socket on the lens/shutter. All with fresh batteries and waiting at least twice the time it takes to fully recycle before firing the flash.<br>

I repeated the same tests with PocketWizards and they performed flawlessly, ie, no differently to when the flashes were connected directly. Yey PocketWizards!<br>

JJ</p>

[pete_s.]

<p>Hi John,</p>

<p>The pocketwizards introduce a delay between the transmitter and the receiver because a radio message has to be transmitted and that takes time. Having measured that delay I found out that it is always exactly 560 microseconds on normal channels. Translated into a more photographer friendly number the delay is slightly more than 1/2000s. So when you sync at 1/500s (2000 microseconds) the PW delay will eat up 25% of that time. Depending on the shutter speed and the flash duration the delay may not be noticeble but it is always there.</p>

<p>Have a look at for instance http://lullaby.homepage.dk/diy-camera/sfld.html to see how a flash behaves when it discharges. Faster shutter speeds cuts of the tail of the flash duration and that is why you loose some power. However with short flash durations the flash cuts of the tail first so now you won't loose any power.</p>

<p>BTW, is there a way to check that the leaf shutter sync at the right time? If it triggers later than it is supposed to that will cut of even more of the tail.</p>

<p> </p>

[pete_s.]

<p>Remember also that when manufacturers mention flash duration in their spec they usually talk about t=0.5. Look at http://www.warehouseexpress.com/webcontent/Images/saves/durationchart.gif to see which part that is.<br /> When they measure output it is of course the entire flash duration.</p>

[picturesque]

<p>Did you just measure with a strobe meter or did you actually take test shots to see whether you are getting the exposure you should be getting?</p>

<p>Metz handle mounts have a full power flash duration of 1/200th. Don't know about the Canon and Nikon strobes.</p>

<p>In addition, flash meters have problems reading flash outside in brighter light. Just like they have problems reading really short duration flashes.</p>

[john_jovic]

<p>Pete, the CRT sreens showing flash output probably explain the results I'm getting. I still didn't expect it to be an issue at 1/500th!<br>

Nadine, the tests were performed with a 1dsMk2 on the back of a Sinar view camera. The 1dsmk2 was set to B and the shutter was opened. The Copal shutter was fired at various speeds (with the flashes attached directly to the PC socket, no radio triggers) and then the 1dsmk2 shutter was closed. Pretty old 'skool' really. The differences in exposure are obvious on the histograms of each image.<br>

JJ</p>

[pete_s.]

<p>JJ, it's funny what you find out when you do thorough test like you did :-) Like your old skool approach. Is it for some type of product photography maybe?</p>

<p>BTW, one of the guys on flickr strobist group ran <a href=" on the Nikon SB800</a> and found out the values below for flash duration. Basically you can't go faster than 1/250s if you want to capture the entire flash pulse on an SB800.</p>

<p>Pwr -- t=0.1 -- t=0.5<br>

1/1 -- 257.73 -- 825.08<br /> 1/2 -- 759.3 -- 821.02<br /> 1/4 -- 1615 -- 1797.3<br /> 1/8 -- 2979.7 -- 3620.6<br /> 1/16 -- 5112.5 -- 7363.8<br /> 1/32 -- 7874 -- 13351<br /> 1/64 -- 11338 -- 22371<br /> 1/128 -- 13661 -- 29674</p>

[picturesque]

<p>Then I'd say we're back to your original hypothesis.</p>

[john_jovic]

<p>Pete, the Flickr link is interesting. I think it is typical of most el'cheapo battery strobes. My Metz 60, Canon 580EXII and Nikon SB-28 all seem to have the same basic charecteristic.<br>

Yes, the tests were basically for some 'product' photography but the products I shoot are rather large, cars to be specific. I very often use the strobes described above to shoot cars but I'm usually balancing them to the ambient conditions and usually using slowish shutter speeds as well. I've started experimenting with Copal shutters and strobes to over power daylight with the strobes and create a different look to that which I've been doing. My strobes are just not powerfull enough to do that at 1/250th but would have been (theoretically) at 1/500th. But as the Grinch said after his crash test in his Christmas Sled, "That's what these tests are for"!<br>

There are lots of examples of the car work I do <a href="http://www.rigshots.com.au/howto3.htm">here</a> and <a href="http://www.rigshots.com.au/howto4.htm">here</a> in case you are interested.<br>

JJ</p>

[pete_s.]

<p>I like your work John, some great shot's in there and good articles as well!</p>

<p>Regarding the strobes you could always double up if you have enough strobes - sandwich two speedlights and run them at 1/2 power. You get faster recycle and double battery life as well.<br>

Otherwise I think that some of the battery powered strobes like Elinchrom Rangers have faster flash duration. I know the H3D2 does flash sync at 1/800s and I heard Tim Flach talking about how he liked that and how he was using battery strobes for shooting animals at 1/800s to underexpose the ambient.</p>

 

[john_jovic]

<p>Thanks Pete.</p>

<p>Yeah, I was thinking about using strobes in pairs at 1/2 power but that's obviously a compromise. Still, better than nothing.</p>

<p>Thanks<br>

JJ</p>

[frank_horn]

<p>My Vivitar 2000 that did good for me for years, died. I left the batteries in it and they leaked.<br>

Is there a good replacement out there? (I don't think this unit is available any more)<br>

It was small. Used 4 AAs. What I would like is something similarly small; $100-150. Auto shut-off.<br>

This is used with a Leica M4-P. Thanks.</p>

<p> </p>

[g._armour_van_horn]

<p>Totally off the original topic ...<br>

 <br>

John, Nice work on those pages. I don't remember where I picked this up, but the one thing that helps me the most with polarizers is that you need to know the electrical resistance of the subject! Reflections from dielectrics (insulators) are polarized, reflections from conductors are not.<br>

 <br>

When you're shooting a car you have dielectrics (glass and paint) and conductors (chrome trim and metal flakes in the paint). When you are are shooting metallic paint you want to kill the specular reflection from the surface of the paint (polarized) so you can show the specular reflection from the metal flakes in the paint (nonpolarized).<br>

 <br>

Note that you need to remember where the reflection is happening. A mirror doesn't polarize light because it's the silver or aluminium layer on the back of the glass that's actually reflecting. The same with the metalized flakes in the paint.<br>

 <br>

Van</p>

[john_jovic]

<p>Van, that's very interesting. Thanks</p>

<p>JJ</p>