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2026-04-30 Checking Flash Calculator Dials Against a Flash Meter


I was writing a review of the Image TFD-45 flash (shown right) when I jokingly thought to myself, “Haven’t I just written about a very similar flash from Vivitar (the Auto Thyrister 550FD, shown left)”. That led to thoughts that I, if I wanted to try, could fire them both up and see how their calculator dials differ, and while I was at it I could see if either of them even approaches the output need to make the calculator dials accurate. I have a Minolta flash meter I could set up in my room (white ceiling, light paneled walls) ten feet away.
    Both flash have two auto ranges (red and blue on the Image, A1(red) and A2(blue) on the Vivitar. Luckily the pair chose the red range for the longest, blue for the shortest.
 
At ISO 100 for the two flash and flash meter—

Flash                 Vivitar 550FD (Nikon) Image TFD-45 (Canon)
Red range at f/2 2-12 m, 6-40 feet         1.3-10 m, 4-30 feet
Blue Range at f/4 1-6 m, 3-20 feet         0.9-5 m, 3-16 feet
Manual at 10 feet 
(Calculator dial)  f/8                                 f/5.6

Flash meter         f/4 + 0.5 stop                 f/2.8 + 0.6 stop

What can we learn from this?
    Not as much as you might think, unfortunately.
    For starters the two flash were built to interface with two different camera manufacturers products.
    The Vivitar was built for Nikon cameras with a switch that changes the flash from FG 20/ FE, A1, A2 and finally M/TTL. It also tilts, but that is another subject.
    The Image flash was built for Canon cameras. It does not tilt. It has a front sensor switch for M, Blue and Red. It does have a wide panel that changes the ranges, but that panel wasn’t in place during the metering. The base of the Image flash has a switch for allowing slow sync as well as a second ASA setting switch. The flash has the same ASA choices, but it doesn’t set anything on the flash, just sets the calculator dials so you can figure out the Auto ranges or pick a manual f/stop for the distance from flash to subject (aka “Manual Mode”).
    The biggest problem with a sudden test of a flash is forming the capacitor hasn’t happened. In the instructions (of yet another flash) it was mentioned you had to recycle the flash to full power, fire it, recharge to full power and repeat that at least three times. Getting to full power takes some time after the ready light comes on (ready lights generally come on at 80 per cent charged). And of course cycling flash takes a lot of power, so as you try to form a flash it takes longer each cycle. It is all too easy to rush the process and ruin exact readings.
    Of course an even better series could have been pursued testing the “Auto” ranges too. But if the manual ”full output” tells you anything, it is to do your own testing to determine how the calculator dials on the flash should be set to get the right amount of light for a proper exposure.

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