YS-01: Not really TTL? Confused ...

[Cosmographer]

My LDS told me today that the YS-01 uses DS-TTL rather than TTL. They explained that this works by measuring the light output of the built-in flash and then replicating that in the YS-01. Is this accurate? If so, I don't understand the point of the YS-01. As far as I can tell, cameras don't adjust the strength of their built-in flashes, do they? You have to adjust flash strength manually, right? So the YS-01 doesn't change its output unless you manually adjust the output of the built-in flash? Doesn't this basically make the YS-01 a manual strobe in that any change in output must be made manually (albeit in camera rather than by the strobe's dial)?

I then asked my LDS why even bother with a YS-01, and they told me it's pointless - better to just go with the YS-02 since I'll be manually adjusting in either case. Something doesn't add up. Where am I going wrong here?

 

[DazedAndConfuzed]

The original TTL flash in the film camera days works by firing off the strobe until the sensor measuring the amount of light bounced off the film stock and shuts off the strobe when it determines enough light has reached the film based on the ISO setting. When digital cameras came around, the sensor was too dark to get any meaningful light reflected off to measure during exposure, thus they came out with strobes that sends off a pre-flash(es), which are short burst of flash, where the camera would determine how underexposed that shot was and adjust the strength accordingly when taking the picture.

If your camera does not adjust how much light to send out of its internal flash, then it would properly expose a subject from only 1 distance on a given ISO/aperture setting.


The way the optical TTL strobes like the YS-01 is that they don't measure the light output of the camera's built in flash, but replicates its duration. It is like a optical amplifier. So when your camera does its pre-flash(es) before taking a picture, the flash's duration is replicated by the YS-01, which because it has higher brightness intensity, will seem to be brighter than if it was coming from the camera's flash, thus when your camera shoots its flash when taking the picture, it does not shoot its flash for as long a period compared to if it was using its own flash to take a picture of the subject. But the brighter external strobe still lights up the subject properly for the camera.

 

[Cosmographer]

Thanks for taking a crack at trying to explain this to me . I don't quite understand how the "duration" of the flash makes an impact. Whether the flash lasts for a split second or whether its constant (like a dive light), as long as the light output is the same, the illumination should be the same right?

 

[DazedAndConfuzed]

a strobe lights up for a very short period of time.

When taking a picture without the flash, it might require your shutter to be opened for 1/30 sec. But when using the external strobe, the shutter speed could be set to 1/250, which makes the ambient light 1/8th what it should be, with the rest of the required light being made up by the strobe.

The flashbulb in the strobe is extremely bright, if would be as bright, much brighter than a HID bulb from a car (but it doesn't have the capacity to keep it lit for that long). It is also of constant brightness (e.g., it isn't like a dimmable bulb, setting off a dim flash or a bright flash). To light up your subject, you don't need it light up for the whole duration of your shutter speed, or else the picture would be way overexposed, so the strobe would based on the pre-flash, maybe light the subject for 1/5,000 sec.

If the subject is farther away or you need more light for other reasons (higher f-stop, lower ISO, etc), then the strobe may stay on for 1/1,000 sec, which would produce 5x more light that the above 1/5,000 sec instance.

So strobe's strenght = brightness * duration

 

[Cosmographer]

Thanks Lwang. This changes the way I've always thought about how flashes in general worked in conjunction with shutter speeds. It'll require some re-learning on my part, I think.

 

[Solomander]

This is a very helpful discussion. I have a Canon Powershot that I have been using with the built in flash and diffuser. If I use an external strobe that works optically does it do everything automatically based on what the camera does, or are there adjustments that need to be made in the external strobe too?

 

[cardog]

My LDS told me today that the YS-01 uses DS-TTL rather than TTL. They explained that this works by measuring the light output of the built-in flash and then replicating that in the YS-01. Is this accurate? If so, I don't understand the point of the YS-01. As far as I can tell, cameras don't adjust the strength of their built-in flashes, do they? You have to adjust flash strength manually, right? So the YS-01 doesn't change its output unless you manually adjust the output of the built-in flash? Doesn't this basically make the YS-01 a manual strobe in that any change in output must be made manually (albeit in camera rather than by the strobe's dial)?

I then asked my LDS why even bother with a YS-01, and they told me it's pointless - better to just go with the YS-02 since I'll be manually adjusting in either case. Something doesn't add up. Where am I going wrong here?

I would go to a different dive shop......
Here are a few pics taken with the Oly E-pl2 and two YS-01 strobes set on s ttl.......

 

[DazedAndConfuzed]

This is a very helpful discussion. I have a Canon Powershot that I have been using with the built in flash and diffuser. If I use an external strobe that works optically does it do everything automatically based on what the camera does, or are there adjustments that need to be made in the external strobe too?

Since it simulates everything the camera's flash does, it should work just like the internal flash. Not sure about things like red eye reduction though.

So the good thing with the optical TTL is that you can set the metering mode to anything you want, be it spot, multi-spot, etc (that is if your camera has those modes with flash lighting), aim the strobe at anything you want, be it aiming it toward behind the subject so you get a very dark foreground/background. If you camera's metering could handle that, then it could also do it with the external strobe.

You will also have to check for compatibility though, since some cameras are not yet compatible with it.

 

[Solomander]

Thanks for clarifying this. I am going to check out an add on strobe before my next trip, which means that my camera will probably get flooded.



Joel