I have a National PE-201C flash, which has the following guide chart:

national pe-201c flash chart

I kind of understand the chart: if I'm standing 3.5 meters away from the subject and have ISO 100 film, I should use an aperture of ƒ/5.6. However, I'm unsure when to use the different modes of the flash and how to they actually affect the exposure. It has two auto modes: green and orange and a mode labeled M (presumably manual).

Can the situations, when to use which, be interpreted from the chart above? I've noticed that in the chart the green auto's line start from 1.2 m and the orange's from 1.8; does it have a meaning or is it decoration? How the ƒ-number can be the same with the overlapping distances — how do the auto modes actually differ? When should I use the M mode and how powerful is that?

The flash being 20+ years old, I probably shouldn't rely on the auto-modes as the light meter might have had happily retired. But, in theory, when to use which?

  • I have the Owners manual and can Scan it if you would like. Regards Brett – user25040 Dec 31 '13 at 23:42

Pentax AF280T is a flash from similar era with similar green and red auto modes. According to its manual, these are "low output" and "high output" automatic modes.

For medium distances, you may use either; for edge cases (closer than 1.8 m or further than 5m on the PE-201C), you have to tell the flash if you need the light thrown carefully or quickly (the distances covered by green and red line should hint that).

So, when you take photos in green mode with ISO 100, set your aperture on 4 and the flash will adjust its power according to light reflecting back on its light sensor. For red mode, set your aperture on 2.8 with ISO 100.

Manual mode very likely just pops at full power each time (easy to verify if you actually have the flash). Out of distance, aperture and ISO, select two as you like and use the chart to select third value to match.

  • Exactly the kind of practical info I sought! I had a hunch that "green" and "red" auto modes had had been somewhat common modes among other old flashes, so I am fairly confident to follow the AF280T's manual for that bit; PE-201C manuals seem to be digitally non–existent. Thanks for the link to Pentax' manual and double–thanks for the answer :-) – Jari Keinänen Jul 18 '11 at 13:20

Manual mode: the flash fires at its full power. You control the amount of exposure on your film by setting the f-stop on your camera. The chart helps you to determine the f-stop to use. The shutter speed is irrelevant to the flash exposure that the film will sense, but ambient (non-flash light) will still expose the film. So, for example, if you are outdoors, using ASA 800 film and a flash sync speed of 1/60 in order to fill-flash a person standing 20 feet from the flash, you will probably over expose the film even if you do set the flash correctly.

Auto mode: the flash has a crude, non-directional sensor on the front of it. This sensor must be unobstructed and pointing at the subject. It is handy, but not always accurate if you are finicky. This flash obviously has two flash intensities that it will use in auto mode. The higher intensity (green) will result in better flash-subject distances, smaller f-stop settings on the camera, and shorter flash durations which might be better for stop-action. It will also probably use up your batteries faster and age the capacitor more. The lower intensity will allow you to use the flash at closer distances or will give you a bit more flexibility in adjusting your fill-flash. Auto modes rely on you or your camera telling the flash what film speed you are using and what the aperture is set to. If you look around you will probably find a way to do that, a dial or a slide switch or something. Or it may rely on an extra pin to get that information from the camera, in which case it would be specific to a particular brand of camera. I have no idea if it is TTL flash capable.

Distance: the distances in this chart are flash-to-subject distances, not camera to subject. It is irrelevant how far your camera is from the subject. You are capturing the light that is reflected from your subject, so what matters is how much light is falling on your subject.

Chart: the full chart is used for manual mode, including the green and red columns. It's just a simple falloff chart. You can even extrapolate the chart out to the right or down to faster film speeds.


You're asking lots of questions here, so I'll just answer the main ones and you should be able to work out the rest.

There are two auto modes to essentially allow you some choice when it comes to aperture (for depth of field purposes). You'd use the orange Auto mode when you want shallower depth of field without too much fussing around with the flash settings, for example.

Manual mode is generally more accurate and allows for more artistic control, but takes a bit more setting up, much the same as with the camera itself.

  • But, apart from the on/off switch, manual flash trigger button and synchro-cord hole, there is no other interface than the green-manual-orange slider. How could I adjust the manual mode; how could it be more accurate if I can't adjust it? Or does the manual mode usually mean that the flash will only trigger if I manually press the flash trigger? And how should I read the chart when using orange auto? Does it say that if I'm standing 3.5 meters away from the subject and having ISO 100 film, I should use ƒ/4 instead of ƒ/5.6? – Jari Keinänen Jul 12 '11 at 11:37
  • You 'adjust' the manual aspect by controlling the ISO, aperture and distance from the subject. The Auto modes seem to be set up for either working at 5 or 7m from the subject - if you want to be at 3.5m, you need to use manual mode. – ElendilTheTall Jul 12 '11 at 12:06
  • 1
    What could be the real difference between green and orange modes, then? I mean, if doubling the distance needs 4 times ("2 stops") more the flash power; multiplying the distance by 1.5 should need 2 times ("1 stop") the flash power — so with that logic, using green auto @ 7 meters would require the same ƒ-numbers as the chart says the orange auto requires @ 7 meters. Or did I miss something? – Jari Keinänen Jul 12 '11 at 12:36
  • I tried to put that into words :-) but isn't the whole chart using the inverse-square law? Going left to right from a column to a column multiplies the distance by √2 and the needed exposure by 2. Shouldn't the rightmost columns be askew if orange auto > green auto? – Jari Keinänen Jul 12 '11 at 14:20

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