What do the distance markings on a Vivitar 273 flash dial mean in auto-thyristor mode?
Asked 8/12/2026
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I’m using an older Vivitar 273 flash and I’m confused by the calculator dial. I understand that the guide-number scale can be used in manual flash mode: for example, with a guide number of 100 (ft) at ISO 100, f/4 gives a distance of 25 ft.
What I’m unsure about is how the distance markings relate to the flash’s auto-thyristor modes. The colored auto ranges on the dial match the expected apertures (for example, yellow = f/4, red = f/5.6, blue = f/8), but the printed distance numbers don’t seem to match the usable auto ranges listed in the manual.
Are the distance numbers on the dial only meant for manual guide-number calculations, while the auto-thyristor mode uses its own separate working-distance ranges? Or should those dial distances also be interpreted as auto-mode distance limits somehow?
Originally by Alana Storm. Source · Licensed CC BY-SA 4.0
Alana Storm
8d ago
1 Answer
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Generated from our catalog & community — verify before relying on it.
Yes — your reasoning is basically correct. On flashes like the Vivitar 273, the numeric distance scale is primarily for manual guide-number use: you match ISO and aperture, then read the flash-to-subject distance for full-power manual flash.
In auto-thyristor mode, the flash uses its sensor to quench output when enough light has returned, so the important settings are the selected auto range/color and the matching aperture/ISO. The usable distance range in auto mode is therefore the separate minimum-to-maximum range specified for that color mode in the manual.
So if the manual says, for example, yellow works from about 3–25 ft, that is the meaningful auto-thyristor range — not the single distance values you’re seeing on the calculator scale.
In short:
- manual mode: use the guide-number distance scale
- auto-thyristor mode: use the color/aperture setting plus the auto range from the manual
The dial may visually overlap these ideas, but the printed distance numbers are not the authoritative auto-range limits.
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AI8d ago
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