ST-IV 's TCM Function vs Flash Meter

The PiXAPRO ST-IV in conjunction with its TTL Convert to Manual (TCM) function, can be used as a great alternative to a flash meter, with any of PiXAPRO’s TTL compatible battery flash systems, such as the CITI600/CITI400 Series, PIKA200, or any of the Li-ion II Series speedlites.

TCM Function

TTL uses your camera’s built-in light meter to determine, how much light is in your current scene, and then works out how much flash power is required to give you correct exposure. To take a reading using the TCM function, simply take a test-shot to see how your images looks. If you are happy with the results, simply press and hold the TCM button on the ST-IV for approximately two seconds, and you are ready to go.  Since the meter in your camera uses “Reflective Metering” (which measures the light reflecting from your subject), the lightness or darkness of your subject’s clothing or skin tone, can sometimes affect the exposure that your camera decides to use. This, however, can easily be tweaked by either adjusting your Flash-Exposure Compensation before using the TCM function, or you can tweak it manually after the TTL has been converted to manual mode.

This function is great for times when you need to quickly get your flash exposure in the ball park, and then tweak accordingly, or for times when it is not possible to go to the place where you are photographing to take a meter reading with a traditional light meter (such as shooting at a concert etc.).


Traditional Flash Meters

Traditional Flash meters use what is called “Incident metering”, which measures the amount of light that is falling onto your subject as opposed to reflecting from your subject. Therefore, the light readings won’t be affected by the colour of your subject’s clothing/skin tone etc. However, taking a light reading with a traditional light meter involves physically walking up to your subject, and taking one or several readings to determine what your exposure settings should be. Once you have taken your reading, you must either set your camera to the exposure settings showing on your flash meter or adjust the lighting to match the camera settings that you require.

Traditional Flash meters are great for times when you have time to set up your shots, or if you want to test your lighting before your subject arrives.


Whilst both Traditional flash meters, and the TCM function, both have their advantages and disadvantages, the TCM function is a great alternative to traditional flash meters. TCM is especially useful in fast-paced shooting environments, such as at weddings or events, where you don’t have the time to measure the light with a flash meter. The TCM function works just as well in situations where you have more time to shoot, such as portrait and still-life shooting sessions etc. It is also one less bit of gear that you have to carry around with you. Even if you traditionally use a flash meter to take exposure readings, the TCM function of the ST-IV can prove to be a great back-up solution should your flash meter stop working for some reason.

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