Copal 00 Shutter and Flash Sync

[gebseng]

Hi everyone,

I am using a Leaf Credo 40 DB with a Linhof Techno and Lenses with Copal 00 shutters.

I recently started using studio flashes and assumed that, with leaf shutters, all shutter times should be equal. But obviously not: when I try 1/60, 1/125, 1/1250 an 1/500, the image gets noticeably darker each time. The room is sufficently dark to not influence the exposure.

What could be an explanation for that?

best,

Geb

[elliot_n]

What flash are you using? Flash duration could be a factor.

[Doug Peterson]

Flash duration and the method of triggering are the two things to consider.

For example a Profoto Air has a shorter lag from pulse to trigger than a PocketWizard Plus II. Hard wired has the least lag of all.

At full power many legacy or cheaper strobes have a relatively long flash duration. If the flash is still outputting power after the shutter closes then that light does not contribute to the exposure.

[Two23]

I agree with above.  While leaf shutters will sync at higher speeds, if the flash duration is a longer burst the high speed doesn't help much.  And there is just a tiny bit of lag using radio triggers.


Kent in SD

[Ken Doo]

Don't forget----that both Profoto and Pocket Wizard (model dependent) have a means to set a "fast trigger" mode to shorten lag time and allow you to take advantage of syncing at higher speeds wirelessly. This does use more battery power in the trigger.  The Phase XF with its built-in Profoto Air does not require setting a "fast" mode.

Ken

[gebseng]

Thanks for your replies! My flash is a Jinbei/Caler ECD studio flash, with a advertised flash duration of 1/1000 at full power, probably even shorter with less power. I will try a setup without wireless triggers to see if that could be the problem.

best,

geb

[Doug Peterson]

Thanks for your replies! My flash is a Jinbei/Caler ECD studio flash, with a advertised flash duration of 1/1000 at full power, probably even shorter with less power. I will try a setup without wireless triggers to see if that could be the problem.

Don’t assume it’s faster with less power. That is generally the case, especially with traditional flash circuitry, but depending on the underlying electronic technology the opposite could be true.

Also, most flash companies spec flash duration in t.5 which is the time during which half (50%) of the power is discharged. By definition that means half the power comes after that time, often in a curve shape that tapers for a considerable period.

If you also have a Phase One XF you can measure the effective/real-world flash duration of the flash since the XF features a built in flash duration meter.

[elliot_n]

With most monoblocks, the flash duration becomes longer as you reduce the power.

[Chris Barrett]

Also, if you're shooting in a dark studio, there's no reason to use a super fast shutter, your shutter speed will be the duration of the strobe.

[Kirk_C]

With most monoblocks, the flash duration becomes longer as you reduce the power.

Actually the opposite is true for most flash generators, both monoblocks and pack/head combos. But there are exceptions.

Most flash put out their shortest duration of light at their lowest power.  There are exceptions of course.

Since Doug mentions Profoto, for example their Pro packs/heads Acute packs/heads, B1, D2 and the old Profoto compacts all put out their shortest duration at their lowest power. The Profoto D1 is just the opposite, putting out it's shortest duration at full power.

Elinchrom, Hensel, Dynalite, Speedotron, Norman and Comet all put out their shortest duration at their lowest power. Dynalite also build their stadium packs and heads with short duration and recycles times at full output (they use Comet's technology and heads since they were bought by Comet.)

Broncolor allows you to set duration on many of their lights but by inherent design put out their shortest duration at lowest power.

The Chinese don't always give their specs clearly but the OP should have HSS available as an option since Jinbei Caler have offered it for years.

[gebseng]

Thanks! Yes, of course shutter speed is not crucial in a darkened room, but it would be less complicated for me if I did not have to care about that at all. About HSS: isn‘t that only relevant for focal plane shutters?

Best

Geb

[elliot_n]

Actually the opposite is true for most flash generators, both monoblocks and pack/head combos. But there are exceptions.

Most flash put out their shortest duration of light at their lowest power.  There are exceptions of course.

You might be right about the high end of the market. I tend to use budget monoblocks (Bowens, Elinchrom, cheap Chinese knock-offs). All of these get slower as you dial them down. (It is easy to test for - just photograph something that is spinning fast (e.g a fan) at different flash powers.)

[elliot_n]

Anyway, regardless of whether this is normal behaviour for most monoblocks, it is clearly the case with the OP's monoblock. The quoted flash duration of 1/1000 sec will be a t0.5 measurement. The more relevant t0.1 measurement will be approx 1/300 sec. This explains the darkening of the image at 1/500 shutter speed. The darkening of the image at slower shutter speeds is explained by the fact the OP is using the monoblock at reduced power — at reduced power, with his monoblock, the flash duration is longer.

[Martin Kristiansen]

Elinchrom flash duration gets shorter at lower power. Well so I am told by their local technician.

Anyway it’s easy to check if this is the problem. In a dark studio set up the flash and shoot with constant power ar varying shutter speeds, keeping aperture fixed of course. Then any variation is due to something other than pier out put. Try it at minimum power and maximum power varying aperture for each set to determine if duration linked to pier is an issue.

I have seen this issue with leaf shutters on technical cameras and with my Leaf AFI in the past. I have some idea it may have to do with the time it takes for the blades to open but I’m not sure

[gebseng]

To get to the bottom of this, I made a strictly scientific-ish test series now:

- I synced via cable, to rule out trigger delays
- I made exposure series (again, in a darkened room) with 1/8, 1/15, 1/30, 1/60, 1/125, 1/250 and 1/500 sec, aperture wide open at f5.6 (SK 72mm in Copal 00 shutter, Leaf Credo 40 DB at 50ASA)
- I made three different series, one with 100% flash output, a second with 12,5% (3 stops down), a third with 3% (5 stops down)

the results:
- at 100% and 12,5%, exposure is stable (+-1/3 stop) from 1/8 down to 1/60, after that it gets noticeably darker
- at 3%, exposure is stable (+-1/3 stop) from 1/8 down to 1/30, after that it gets noticeably darker

So, maybe it's the leaf shutter after all?

best,

geb

[Martin Kristiansen]

I wonder if it makes a difference what aperture. If it’s the time it takes for the shutter blades to open as a percentage of exposure then it makes sense it will be more noticeable at faster shutter speeds.  Try at different apertures. If the effect is less noticeable with a small aperture than a large aperture then it is the shutter blades opening that causes the effect. Takes longer for the blades to clear a large aperture if you know what I mean.