disable A70 preflash?

[fudgeorama]

How do you turn off the preflash on a powershot a70? Or how do you fool a slave flash to ignore the preflash?

 

[Web Monkey]

You can turn off all the lights using the menus.

It's buried pretty deep in the menu structure, but you can get the manual here:

http://beta00.c-wss.com/inc/servlet...adFiles_inc/00008313EN0106/PSA70A60CUG-EN.pdf

and it gives directions for both.

Terry

How do you turn off the preflash on a powershot a70? Or how do you fool a slave flash to ignore the preflash?

 

[fudgeorama]

From the manual, it appears the only way to turn off the preflash is to turn off the flash altogether, but then you have no way to trigger an external slave flash right?

 

[Web Monkey]

From the manual, it appears the only way to turn off the preflash is to turn off the flash altogether, but then you have no way to trigger an external slave flash right?

That's interesting

You apparently can't directly disable it, however I beleive it only fires once if you select "manual" mode.

Terry

 

[tedtim]

How do you turn off the preflash on a powershot a70? Or how do you fool a slave flash to ignore the preflash?

What type of sensor are you using? I use the Ikelite EV controller with my A70. The controller has a switch setting to deal with the pre-flash.

 

[bobf]

The flash of an A 70 set to manual mode will produce only one optical signal in sync with the shutter event. That signal can be set from low to full ( which actually controls duration).

Given the option, it would be better to avoid the preflash. By doing so, you will increase battery performance and decrease housing heat (chance for fogging of lens). Choosing the least powerful signal strength to trigger an optical slave flash will offer similar benefits.

 

[fudgeorama]

In manual mode, don't you have to set all the other options (aperture, ISO, etc.), thereby losing the point and shoot ability? As tedtim pointed out, maybe I have to upgrade to a digital slave strobe that can either ignore or mimic the internal flash.

 

[bobf]

In manual mode, don't you have to set all the other options (aperture, ISO, etc.), thereby losing the point and shoot ability? As tedtim pointed out, maybe I have to upgrade to a digital slave strobe that can either ignore or mimic the internal flash.

I recommend setting the ISO to anything other than auto. Keeping the sensitivity setting at or below ISO 100 will minimize "grain".

Setting the proper aperture and shutter speed is not difficult with digicams that offer manual mode. There is usually a guide in the LCD screen that advises you how over or under exposed your chosen settings will capture the composition. The Exposure Value readout will display a number between plus or minus 2 EV's. Simply alter the "equation" between aperture and shutter until the desired EV readout is displayed. Sometimes you may wish for a slightly underexposed image. If so, target the EV readout to be between -0.3 and -0.7 EV, possibly more if you wish for a darker background exposure. Try to avoid any overexposure readings (EV's on the plus side). I also recommend setting the shutter speed to no less than 1/100 sec unless your buoyancy skills are top notch.

Choosing a strobe operating system is also a question to be addressed. TTL, Auto, or manual are your choices. Choose one and if you'd like, we can discuss it.............

hth,
imho,
b

 

[fudgeorama]

I have borrowed my friend's slave strobe and played around in manual mode in a dark garage to simulate a dark cavern. I kept the ISO at 100 and tried adjusting the other values to get them higher than -2, but could not without adding some ambient light. How do you avoid the pictures turning out grainy? How does the camera know that you will be adding a lot of light with the strobe and adjust accordingly?

 

[bobf]

How do you avoid the pictures turning out grainy?

Choose a low sensitivity setting, never auto. ISO 100 or less should keep the "grain" or noise to a minimum.

How does the camera know that you will be adding a lot of light with the strobe and adjust accordingly?

The camera in manual mode does not do any of the thinking. You dictate to the camera that you want it to force the flash by selecting from the flash menu the proper actions. The flash when properly set will expose the foreground.

The "foreground" is any part of the composition that is influenced by strobe light. By definition therefore the foreground underwater must be within distance of the maximum power of the strobe (5-6 feet or so).

The foreground exposure is controlled by the aperture along with the intensity (power) of the strobe. The strobe's intensity may be controlled in various ways. TTL, auto, or manual. You mentioned that the strobe was your friend's. Can you provide more details of the strobe please.

If your goal is to recreate a technique that will illuminate a whole cavern with a single strobe without "grain", it may be quite a challenge.

I kept the ISO at 100 and tried adjusting the other values to get them higher than -2, but could not without adding some ambient light.

The background, any part of the composition not directly influenced by strobe light, is controlled by the values you mentioned, aperture and shutter speed. Depending upon low light conditions, you may not be able to increase the EV readout above -2 underwater by manipulating the shutter speed (you may be forced to go too slow for hand held use). There may just not be enough ambient light present, especially in a cavern. If that is unacceptable, then you may have to alter your shooting goals. However an EV of -2 is not necessarily a bad thing. A dark background can be very dramatic.

If your goal is to capture a background scene within a cavern devoid of sufficient ambient light, you may have to sacrifice image quality and increase ISO sensitivity.