Explain to a complete novice how this flash calculator works

[yessammassey]

Things I've learned from basic observation, or asking others so far:

1.) It's a Vivitar flash. The kind you can plug in or use with batteries. The built in PC sync cord is nice. Now I have a flash that will work with my RB67.
2.) It has three modes, blue (for subjects up to 9ft away), orange (subjects up to 17ft away), and M (???)
3.) You set the ISO on the dial and it tells you what aperture to use to illuminate a subject at that distance. I guess if you're using M mode, you just figure the subject distance and set the aperture as indicated.
4.) Don't use it with an electronic camera!

Things I think I understand, but am not sure:
1.) Guide number is 64ft @ ISO100. So with ISO100 film at f/8, it would illuminate a subject 8ft away.. right?
2.) Flash output can vary... according to what color is set? Output on blue mode is less than output on orange? M is always full output? It varies output by duration of flash?

Things I've yet to figure out:

1.) I think I can calculate which aperture to use depending on ISO and subject distance, but how do I determine which shutter speed to use? My RB67 can sync at any speed. My FM can sync at 1/125 and below.
2.) Following from question 1: How do I use this flash to keep my shutter speed up in low-light conditions? Say I have a scene where the subject is 8ft away, and my meter gives 1/30 at ISO100 & f/8. Can I use the flash to bring up by shutter speed to 1/125 at f/8?
2.) Blue mode if for subjects up to 9ft away, while orange is for up to 17ft. Why is there no minimum distance for orange mode? Wouldn't it overexpose at closer distances, compared to the blue mode? That's assuming blue mode and orange mode have different output levels...

These might seem like basic questions, but I come from the land of digital cameras with TTL flash, and even then I use a lot of [shoot, look at image, adjust flash exposure compensation, shoot again, look again, adjust again] to dial in the look I want. I've never used flash enough to develop a real working knowledge of the principles behind it. I get the relationship between the aperture number and distances on the dial (and how illumination varies according to the squares of those numbers.. in a basic sense), but I've no practice in actually applying that information.

 

[MattKing]

2.) Flash output can vary... according to what color is set? Output on blue mode is less than output on orange?

2.) Blue mode if for subjects up to 9ft away, while orange is for up to 17ft. Why is there no minimum distance for orange mode? Wouldn't it overexpose at closer distances, compared to the blue mode? That's assuming blue mode and orange mode have different output levels...

The two modes don't necessarily give different outputs. The circuitry in the flash just cuts off the flash when enough light bounces back from the subject. For that calculation to work with your camera, the aperture setting on the camera need to match what the guide on the flash indicates respecting the film ISO and the aperture set.

By changing the mode, you are just telling the flash that your camera will need more or less at the margins in order to "be fulfilled" But if you set the camera to the right aperture, and you are working at something like 7 feet away from your subject, either mode will be properly exposed. In that circumstance, if it is a Thyristor type circuit, the orange setting will use less energy, and the recycle time will be shorter.

1.) I think I can calculate which aperture to use depending on ISO and subject distance, but how do I determine which shutter speed to use? My RB67 can sync at any speed. My FM can sync at 1/125 and below.

You use the flash to control the flash component of your lighting. You use a regular meter to measure the contribution of the ambient light. You use your head to determine how to balance the two, and adjust the shutter speed to accomplish that.
On the FM, be careful to keep the shutter speed within the range that synchs properly. On the RB67, be careful that you aren't using a shutter speed that is so slow that it will contribute a blurred image from that ambient light.

 

[Bill Burk]

This is a "Thrysistor" flash, which quenches the flash automatically when sufficient exposure has bounced back to the sensor. The cool thing about "Thrysistors" is that they don't waste the extra charge, they leave it in the capacitor. So you recycle faster if you didn't use much of the power, and your batteries last longer.

Blue and Orange are different "Auto" modes... you dialed in 400. For Blue, set f/8. For Orange, set f/16.

Clearly the flash is going to reach farther at f/8 than it will at f/16.

So the two different auto settings let you shoot anything from 4 feet to 10 feet at f/16 (Orange)... anything from 4 feet to 20 feet at f/8 (Blue).

In M mode, you'll have to keep track of the distance and set the f/stop opposite that distance.

 

[AgX]

1.) Guide number is 64ft @ ISO100. So with ISO100 film at f/8, it would illuminate a subject 8ft away.. right?

Guide Number is a unit-less figure, thus:

GN (feet@ISO100) = 64

Maybe you meant this, but then feet or meter designation belongs at the GN.

 

[wiltw]

Things I think I understand, but am not sure:
1.) Guide number is 64ft @ ISO100. So with ISO100 film at f/8, it would illuminate a subject 8ft away.. right?
2.) Flash output can vary... according to what color is set? Output on blue mode is less than output on orange? M is always full output? It varies output by duration of flash?

1. Yes. GN = distance * f/stop.
2. NO...the output is exactly the same, regardless of Blue vs. Yellow!!! In the photo blue zone 20' is at f/8 edge... 20 * 8 = 160. But the yellow zone 10' is at the f/16 edge... 10 * 16 = 160. Whoa...SAME Guide Number in both case, same output in both cases!!!

The color zones merely are a visual cue about what distance range is the MAXIMUM distance that the flash will render a proper exposure...when the lens aperture is set to f/8 or f/16, respectively.

Things I've yet to figure out:

1.) I think I can calculate which aperture to use depending on ISO and subject distance, but how do I determine which shutter speed to use? My RB67 can sync at any speed. My FM can sync at 1/125 and below.
2.) Following from question 1: How do I use this flash to keep my shutter speed up in low-light conditions? Say I have a scene where the subject is 8ft away, and my meter gives 1/30 at ISO100 & f/8. Can I use the flash to bring up by shutter speed to 1/125 at f/8?
2.) Blue mode if for subjects up to 9ft away, while orange is for up to 17ft. Why is there no minimum distance for orange mode? Wouldn't it overexpose at closer distances, compared to the blue mode? That's assuming blue mode and orange mode have different output levels...

These might seem like basic questions, but I come from the land of digital cameras with TTL flash, and even then I use a lot of [shoot, look at image, adjust flash exposure compensation, shoot again, look again, adjust again] to dial in the look I want. I've never used flash enough to develop a real working knowledge of the principles behind it. I get the relationship between the aperture number and distances on the dial (and how illumination varies according to the squares of those numbers.. in a basic sense), but I've no practice in actually applying that information.

So the two different auto settings let you shoot anything from 4 feet to 10 feet at f/16 (Orange)... anything from 4 feet to 20 feet at f/8 (Blue).

1. With a focal plane shutter camera (e.g. Mamiya M645) you must use the X-synch shutter speed as the FASTEST speed you can use with electronic flash...at that speed (or at any slower speeds) the two curtains of the focal plane shutter are FULLY open when the electronic flash emits its light. But when a faster shutter speed is used, the focal plane shutter's two curtains form a narrower SLIT which does not fully expose the entire frame to the flash when it emits its light...a problem seen as a properly illuminated area as well as a darkly illuminated area of the frame! So use 1/125 or slower whenever you use electronic flash...slower speeds when you want the ambient light to contribute some of the exposure of the film (a.k.a. 'dragging the shutter'), faster speeds when you want ambient light to contribute less.
   Cameras with lens-shutters (e.g. Hasselblad) have leaf shutters which have no 'partly open' mode, so flash synch can happen at generally all available shutter speeds (not merely at the X-synch speed and slower, as in focal plane shutter cameras)
2. In the example settings, ambient-only exposure is 1/30 f/8 at ISO100; if you set shutter to 1/125, the ambient-only exposure is underexposed by -2EV, in comparison. So by using flash, it would appear that 'only the flash illumination' will be recorded on the film, but subject motion will be frozen (no ghost image from ambient being recorded). If, however, you set the shutter to 1/30, the ambient light will allow motion blur to be recorded. Regardless of whether you set 1/30 or 1/125 on your shutter, the electronic flash outputs the identical amount of light, in 1/1000 of a second (or whatever flash duration your flash uses)...faster than the shutter itself.
3. I am afraid that Bill Burk's statement (4-10' and 4-20') is not necessarily correct!
   The mininmum distance is determined by the reaction time of the flash circuitry to cut off the flow of electricity to the flashtube...and the minimum distance is determined by that fractional electricity cutoff. The minimum distance can vary based upon the selected lens aperture setting. For one example, a Vivitar 225 can work with a BlueZone aperture which is restricted to the range of 3'-12', while the RedZone aperture restricts it to the range a 5'-24'. Its full power GN is about 68, and its fractional output is GN14...a bit less than 1/8 of full power.
   Read the owner manual for your flash to find out exactly what your flash range is capable of achieving...as your calculator dial does not seem to provide any visual indication about minimum ranges, whereas the Vivitar 225 has such range indication. In comparison, the Vivitar 253 ranges are 2'-17.5' and 2'-8.5'...its ranges do not vary based upon selected aperture.

 

[Bill Burk]

wiltw,

You are correct I made a couple mistakes... I just checked.

First off... I assume this is a Vivitar Auto 252 because it looks just like mine.

I mistakenly assumed since it's similar vintage to a Vivitar 283 that it would have the Thrysistor circuitry. While testing, it seems to me the entire capacitor charge is spent for every exposure. So I was wrong and you won't have the battery life that a Thrysistor would give you, because with every flash in auto mode, after the circuit has detected enough light, the rest of the charge is "dumped" instead of saved.

A quick look in the manual (quick Google search of "Vivitar 252" and "Butkus manual" will turn it up quickly)... shows the close distance to be 2 feet.

I set my flash the same as your picture, yessamassey. Then I set my Sekonic L758 to ISO 500 and fired the flash in blue, red and M from a variety of distances.

This is what I got:

Blue, 9 feet, f/8.0.0
Blue, 6 feet, f/5.6.7
Blue, 3 feet, f/8.0.5
Blue, 18 inches, f/8.0.0

Red, 9 feet, f/8.0.6
Red, 6 feet, f/11.3
Red, 3 feet, f/11.9
Red, 18 inches, f/22.1

M, 9 feet, f/8.0.0
M, 6 feet, f/11.0
M, 4 feet, f/16.2
M, 2 feet, f/32.9

I found that as I moved closer than 18 inches in either Automatic mode, the f/stop increased. So wiltw is right. Closer than 2 feet, you can expect the automatic mode to not be effective at cutting off the flash.

 

[AgX]

Many autoexposure flashes do not indicate a minimum distance at their dials.
One either has to check the manual or do a test/metering.

 

[Bill Burk]

I think it's pretty funny... as I was saying goodbye to my brother-in-law... he reached in his van, pulled out a leather bag with a few camera-related things in it to give me... including... yup. Another Vivitar Auto 252.

 

[yessammassey]

Ok, thanks for the replies everyone. I am coming off a full day of post-thanksgiving driving (my holiday destination lacked any sort of internet connectivity whatsoever, so I'm playing catch-up) so I'll to save my thinking for tomorrow... but I'm still going to post!

While I digest everything explained above, and prepare to go over the manual that user Ian C kindly linked, I am going to ask some questions that I could probably answer for myself if I had internalized everything posted already, but if someone feels like replying before then, great!
...

Let me see if I have this straight. This flash does have a basic light meter, and thus can vary the duration of its output depending on how much reflected light it senses coming off of the subject. Because it's using the magic of electronics, it is capable of continuously measuring the reflected light until it has what it deems to be a proper exposure (on the 15º spot that the flash can sense), then cuts out.. all within 1/1000th of a second or less.

This '1/1000th or less' is important, because it means that the flash exposure will always be the same no matter the shutter speed, as long as the flash is going slow enough to sync (with a focal plane shutter).

What this means is that, in a completely dark room, I could expect to use a shutter speed of e.g. 1/15 and still freeze action on a moving subject, right? As the flash is the only source of light, and only illuminates the scene for a much shorter fraction of a second.

So for a more typical but still ideal theoretical situation, say a performer on a stage, standing well in front of a curtain...

• There is no directional light pointed at the performer. The performer is taking up about 1/5th of the frame, 12ft away from the photographer, and the curtain is 8ft behind the performer.

• Film speed is 400. Nothing else is visible in the frame except the curtain and the performer. The aperture is set to f/11 as per the calculator ring. 'Blue' auto setting is used. With the flash, the subject will be properly lit at f/11 no matter the shutter speed (considering possible sync speeds are from 1/1 to 1/125). (?)

• The camera's center-weighted averaging meter reads 1/60 at f/11. The photographer has shaky hands, but doesn't want the background to be blurry, so they choose 1/125 as their shutter speed.

How much light from the flash reaches the curtain in the background? (I'm not sure)

a) The curtain is 20ft away, so the flash doesn't reach it at f/11

b) The curtain is 20f away, and the indicated aperture for 20ft is f/5.6, so the light that reaches the background is 2 stops less than needed for proper exposure of the scene as read by the flash. This may be a negligible amount.

How much non-flash light from the scene will be recorded by the camera at 1/125?

• 1 stop less than what the camera meter gives as correct (which is 1/60)

How much total light is recorded by the film during exposure, with flash?

• 1 stop less than what the camera meter gives as correct, plus however much light reaches from the flash (which is either nothing, or a very small amount)

Ok, so what about the performer? The flash is going to light the performer until the flash's sensor tells it to cut out. At 1/125, there shouldn't be much to worry about, but say the photographer instead chose the 'correct' exposure of 1/60.

• The camera is already taking in enough light to properly exposure the subject at 1/60, so any flash output is going to be in excess of the light needed for proper exposure at that speed. This means the subject get overexposed? So calculating fill flash is going to be a pain, no?

 

[MattKing]

Does your head hurt yet?

If there is enough light around to give you proper exposure when the camera is set to 1/60 at f/11, you either don't need a flash, or the best use of the flash is to provide an accent or fill light. Using the flash in that circumstance becomes more an issue of balancing sources of light, rather than the more usual use of a flash as your main light source.

You can use the auto sensor on the flash when it is your fill or accent source, but different flashes perform in slightly different ways when used that way. You need to test yours.

I have a couple of flashes that I use that way (for fill). In essence, I use them with the auto sensor set to one aperture, but the camera set to one stop smaller. So the fill light from the flash would underexpose the subject by one stop, if the fill flash was the only source. That fill adds to ambient in a way that lightens shadows and improves modelling.

 

[AgX]

(on the 15º spot that the flash can sense)

I do not know of any autoexposure flash where the angel of coverage of its internal cell is stated.

 

[AgX]

This '1/1000th or less' is important, because it means that the flash exposure will always be the same no matter the shutter speed, as long as the flash is going slow enough to sync (with a focal plane shutter).

The flash does not need to be slow enough to cope with the shutter (though there are some long exposure incandescant flash bulbs and some stroboscopic electronic flashes.)
The standard approach though is too set a shutter "speed" that still yields a moment where the focal plane shutter is completely open. This would mean the sync-speed or slower.


There are some electronic studio flashes (high output) that have such a long exposure time that with leave shutters (central shutters) set at highest speed, the flash might be too long to yield all its effectivity.


Your questions though go beyond what a forum can offer, you sure should read a textbook on that topic.

 

[Theo Sulphate]

... The camera is already taking in enough light to properly exposure the subject at 1/60, so any flash output is going to be in excess of the light needed for proper exposure at that speed. This means the subject get overexposed? So calculating fill flash is going to be a pain, no?

I may be wrong, but I'll toss the question out: isn't this the situation where having TTL flash is an advantage over Automatic mode?

 

[wiltw]

I may be wrong, but I'll toss the question out: isn't this the situation where having TTL flash is an advantage over Automatic mode?

No inherent advantage...although nTTL would theoretically have an advantage in 'seeing what the lens sees' vs. the Auto photosensor flash seeing a set AOV regardless of lens mounted on camera.
In the case of nTTL accuracy of exposure, no inherent advantage there, either (although Canon is well recognized for having blown External mode (Auto photosensor flash) accuracy over the years in the 580EXII and 600EX-RT with underexposing by -2EV, when other Auto flash manufacturers get it right!)

Here is Metz 54MZ in Canon eTTL mode (left) vs. in Auto flash mode (right)...

...the fundamental shot ISO200, 1/200 f/11 on the left and ISO200 1/40 f/11 (Av mode selected speed based upon changing lighting) would have been -4EV underexposed in the shaded areas without the flash.
Since the current discussion happened to be about fill flash, I deliberately chose a fill flash situation (although the sun lit are is a bit overexposed) to illustrate, but the ambient lighting from outside was variable, making a truly direct comparison challenging to accomplish.

 

[John Koehrer]

What color's the curtain?
If dark,, your subject will be overexposed because the sensor isn't selective enough to separate
the subject from the curtain....,.The curtain having 5X influence on the exposure.
If light there may be enough light to give a more even exposure

 

[darkroommike]

I may be wrong, but I'll toss the question out: isn't this the situation where having TTL flash is an advantage over Automatic mode?

It's a big advantage when shooting with a macro lens or bellows since the effective apertures are much smaller that those actually marked on the lens when doing extreme close ups. At 1:1 a marked f/8 is actually f/16. In cases like this the "sensor auto" will under expose by 2 f-stops whilst TTL will be right on.

 

[Diapositivo]

I may be wrong, but I'll toss the question out: isn't this the situation where having TTL flash is an advantage over Automatic mode?

Actually this is a situation where the thyristor might be better than TTL flash. TTL flash measures a certain area typically at the centre of the frame. If you have a small subject (let's say, a dancer who is kneeling, thus occupying a small part of the frame, and maybe he's not in the centre as well) the thrystor is reputed to be more like to cut the light flow accurately, especially if the subject is not in the centre of the frame. TTL measuring would wait for enough light to have cleared the centre portion of the frame, which is mostly a far background, thus overexposing the nearer subject. TTL flash is not ideal for macro photography with far background and off-centre subject.
Thyristors tends to cut when the nearest subject is reached.
If you have three subjects at different distance, let's say left-near, centre-middle, and right-far, TTL-flash will expose correctly the subject in the centre, thyristor will expose correctly the subject at the left, the nearest one.

In this situations manual exposure works generally well. The best automatic exposure would be Autofocus-linked flash exposure. Flash exposure is calculated for the distance where the focus is set. I suspect some compact auto-focus, such as my Yashica T3, follow that logic to drive the the little built-in flash. No doubt some AF TTL reflex do the same with the flash duration governed by the camera if a dedicated flash is used.

The advantage of a thyristor flash instead of using it manually, when the distance is known in advance, is that with thyristor the flash output is less than maximum and the flash duration is shorter, which allows to freeze a fast movement.
In manual mode a flash outputs its maximum power (unless it has a partial-power mode, some flashes have that as well).

 

[wiltw]

Actually this is a situation where the thyristor might be better than TTL flash. TTL flash measures a certain area typically at the centre of the frame. If you have a small subject (let's say, a dancer who is kneeling, thus occupying a small part of the frame, and maybe he's not in the centre as well) the thrystor is reputed to be more like to cut the light flow accurately, especially if the subject is not in the centre of the frame. TTL measuring would wait for enough light to have cleared the centre portion of the frame, which is mostly a far background, thus overexposing the nearer subject. TTL flash is not ideal for macro photography with far background and off-centre subject.
Thyristors tends to cut when the nearest subject is reached.
If you have three subjects at different distance, let's say left-near, centre-middle, and right-far, TTL-flash will expose correctly the subject in the centre, thyristor will expose correctly the subject at the left, the nearest one.

I thought I would do a brief test of the above theory, about photosensor Auto vs. TTL flash. I think the complication is the generalization about 'TTL flash measures a certain area typically at the centre of the frame.' In the case of Olympus OM-4, the TTL sensor reads the film plane when the shutter is open, and tells the flash to cut off, and I do not believe there is a bias to the center of frame. In this test, I used a (gasp...) digital camera with photosensor Auto flash, then with nTTL. And to see if there was any bias toward center of frame in nTTL, I took a shot with subject centered and then with the subject definitively NOT at center. In the case of this camera, TTL is supposed to be biased to the AF zone(s) at the focus distance...which in this case I used center AF point but then recomposed shot 3 framing, leaving the AF point on top of the background!

I see no difference in photosensor Auto vs. nTTL flash.