Can any one explain t-01 times?

[mattcantsk8]

I've heard about them but I have absolutely no idea how they affect the image

 

[tirediron]

Well... you're one up on me; I've not even heard of them!

 

[Overread]

Ack there's a good youtube video on flash units which describes t times. However I can't find it

But in its basic form from what I recall its basically the t time is basically the duration of the flash exposure - ergo how long the flash is emitting light. (that is if I've got the right t).

 

[WayneF]

I've heard about them but I have absolutely no idea how they affect the image

t.5 and t.1 are common terms for flash duration, but I've never heard of t.01.

Flashes have a rapid strong peak of light, and then slowly fades away (relatively slowly, a few milliseconds). It's a lingering decay, and it's hard to say when the duration reaches zero. No one much cares when it finally reaches zero.

Engineers tend to measure things at the half power points. So expediently (and precisely), they measure its half power points (at half of peak), called t.5, which is easy to measure, but not very meaningful to photography exposures. But nevertheless, ISO flash specifications of duration are standardized at the half power points. There is more light left though, which does affect our photographs exposure. But the engineers are more concerned with an accurate measurement, meaningful to them.

So there are also t.1 measurements, when 90% of the light is seen, down to the 10% level. The flash decay is a standard RC curve, well studied, and t.1 is routinely considered to be 3 times longer than t.5. This is more meaningful to photography, however unless otherwise stated, flash specifications are the t.5 standard.

The above is true of most studio monolights, which implement lower flash power by adjusting the voltage on the flash capacitor to lower voltage for lower power. So at less than full power, this makes them slower (maybe 2x longer at 1/32 power), and also shifts the white balance temperature lower (more red, cooler).

Speedlights are made different. The above is all true of their Full power, but their lower powers are always full voltage and full power (after recycle), but implemented by then simply interrupting the current flow to the flash tube (thyristor type, IGBT chips today)... like a switch, to stop it instantly. So then the light does not decay away, but is simply chopped off, instantly. This makes the duration be extremely fast at lower powers, hence the name speedlight, which is the standard way to freeze difficult motion.

Since speedlights chop off the lower powers, they become much faster at low power. And since the cool tail is chopped off, they become more blue. Both effects are the opposite in (almost all) studio monolights.

Here are the specifications for the Nikon SB-800 flash duration (Nikon puts specs in the flash manual).

1/1050 sec. at M1/1 (full) output
1/1100 sec. at M1/2 output
1/2700 sec. at M1/4 output
1/5900 sec. at M1/8 output
1/10900 sec. at M1/16 output
1/17800 sec. at M1/32 output
1/32300 sec. at M1/64 output
1/41600 sec. at M1/128 output

Full power is still a NON-truncated tail, slowly decaying in the standard way. 1/1050 is the standard t.5 time. t.1 time would be 3x longer, or 1/350 second (and more meaningful, photograph exposure wise).

But 1/2 power is truncated, chopped off. The spec time is about the same number, only because Full power is t.5, measured at half power points. But actual 1/2 power is chopped off, and actually stops at the 1/1100 second. 1/2 power is about 3 times faster than full power.

All the lower powers are chopped off, and thus are accurate duration measurements. 1/32 power and 1/64 power levels are extremely fast, and can stop hummingbird wings (but the flash has to be pretty close at low power, in a more dim ambient).

This method is named "speedlight", because they can stop fast motion.

You might be interested in seeing Capability of flash units for high speed photography

 

[tirediron]

Great post Wayne... I just learned a whole bunch from that. Thanks!

 

[WayneF]

Thanks, I'm pleased if it is is useful. But the moderators here might remove my link. They've started doing that, advising that I'm welcome to post my stuff on this site instead. That's not likely.

 

[Overread]

That rule extends to the "interesting articles" subsection and is designed to prevent users abusing the section by simply posting "links" to their off-site articles - ergo simply fishing for clicks. We also exercise this rule in a more lax form outside of the section - although generally only in targeting adbots and clear attempts to harvest clicks and traffic.

 

[WayneF]

Sorry, it looks very different to me. I posted in THIS LIGHTING SECTION a link to a pretty good review of the Neewer VK750 II flash, which is an overwhelming bargain ($54) for an actually very nice flash. I thought it was plenty useful information, esp to those postponing flash due to prices in hundreds.
You can judge it: Review of the Neewer VK750 II Speedlight

But the moderator chopped it a couple of weeks ago, and left it useless to any one. Invited me to post it here. I thought that was pretty poor. It's OK, I can post in other sites.

 

[Dave442]

Nice. I think I will finally remember some of this.

 

[mattcantsk8]

I've heard about them but I have absolutely no idea how they affect the image

t.5 and t.1 are common terms for flash duration, but I've never heard of t.01.

Flashes have a rapid strong peak of light, and then slowly fades away (relatively slowly, a few milliseconds). It's a lingering decay, and it's hard to say when the duration reaches zero. No one much cares when it finally reaches zero.

Engineers tend to measure things at the half power points. So expediently (and precisely), they measure its half power points (at half of peak), called t.5, which is easy to measure, but not very meaningful to photography exposures. But nevertheless, ISO flash specifications of duration are standardized at the half power points. There is more light left though, which does affect our photographs exposure. But the engineers are more concerned with an accurate measurement, meaningful to them.

So there are also t.1 measurements, when 90% of the light is seen, down to the 10% level. The flash decay is a standard RC curve, well studied, and t.1 is routinely considered to be 3 times longer than t.5. This is more meaningful to photography, however unless otherwise stated, flash specifications are the t.5 standard.

The above is true of most studio monolights, which implement lower flash power by adjusting the voltage on the flash capacitor to lower voltage for lower power. So at less than full power, this makes them slower (maybe 2x longer at 1/32 power), and also shifts the white balance temperature lower (more red, cooler).

Speedlights are made different. The above is all true of their Full power, but their lower powers are always full voltage and full power (after recycle), but implemented by then simply interrupting the current flow to the flash tube (thyristor type, IGBT chips today)... like a switch, to stop it instantly. So then the light does not decay away, but is simply chopped off, instantly. This makes the duration be extremely fast at lower powers, hence the name speedlight, which is the standard way to freeze difficult motion.

Since speedlights chop off the lower powers, they become much faster at low power. And since the cool tail is chopped off, they become more blue. Both effects are the opposite in (almost all) studio monolights.

Here are the specifications for the Nikon SB-800 flash duration (Nikon puts specs in the flash manual).

1/1050 sec. at M1/1 (full) output
1/1100 sec. at M1/2 output
1/2700 sec. at M1/4 output
1/5900 sec. at M1/8 output
1/10900 sec. at M1/16 output
1/17800 sec. at M1/32 output
1/32300 sec. at M1/64 output
1/41600 sec. at M1/128 output

Full power is still a NON-truncated tail, slowly decaying in the standard way. 1/1050 is the standard t.5 time. t.1 time would be 3x longer, or 1/350 second (and more meaningful, photograph exposure wise).

But 1/2 power is truncated, chopped off. The spec time is about the same number, only because Full power is t.5, measured at half power points. But actual 1/2 power is chopped off, and actually stops at the 1/1100 second. 1/2 power is about 3 times faster than full power.

All the lower powers are chopped off, and thus are accurate duration measurements. 1/32 power and 1/64 power levels are extremely fast, and can stop hummingbird wings (but the flash has to be pretty close at low power, in a more dim ambient).

This method is named "speedlight", because they can stop fast motion.

You might be interested in seeing Capability of flash units for high speed photography

Thank you so much for clearing that up and going into such detail!