How use a simple auto-tyristor flash in these situations?

Hi everyone

I have a very simple auto-tyristor flash that has a manual mode. Beyond switching between these modes (by moving a cover in front of the tyristor) there are no other settings.

I am wondering how to use this flash with my M6TTL (1/50 sync speed) and Velvia 100 in the following two situations:

1) as a small fill flash on the street at closer distances, and

2) as a bounce flash for people shots in daytime interiors.

I guess what I am wondering is which mode works the best in which situation?

Thanks very much in advance
Philip

Auto mode measures the light reflected from the subject and cuts off the flash when sufficient light has been measured. However it ought to have some way to tell the flash the ISO and aperture being used, so it knows how much light is required. It is possible though that the flash has a fixed light level "baked in" and just requires that you set a particular aperture depending on the ISO of the film. The manual should tell you this. Once this is set up, you should be able to use auto flash mode for bounce flash - just ensure the light sensor on the flash is pointing towards your subject. The fact that the light is bounced shouldn't affect flash operation provided the flash is powerful enough, since the auto flash function should switch it off when it has received sufficient light back from the subject. Of course bouncing requires a more powerful flash than direct flash illumination, so maximum subject distance may be limited or you may have to use a faster film to compensate.

To use fill flash with auto, you want the flash to cut off when 1-2 stops LESS light has been received than is required to properly expose the subject. Once you've determined how the ISO/aperture setting works, you can achieve this by telling the flash that the ISO is a stop or two higher than it actually is (for example, set ISO 400 when using ISO 100 film) or by closing the aperture down by a stop or two. For example, if the flash expects you to be at f/2.8 with ISO 100 film, you could set f/5.6 while using ISO 100 film to bring the flash down by 2 stops for fill.

Alternatively you can use manual mode for fill if you know the flash guide number and subject distance. Assume the guide no is 30' at ISO 100 and the subject distance is 6 ft. Then for flash-only exposure, when using ISO 100 film your aperture should be f/5 (because 30/6=5). Closing down by a stop and a bit to f/8 should give you reasonable fill flash. Of course your shutter speed should be set for proper exposure under the ambient lighting at f/8. However since this flash sounds like it will only fire at full power in manual mode, you might find that it is difficult to get a satisfactory shutter speed if the aperture required to bring the flash level down for fill is too small, resulting in a very slow shutter speed being required for the ambient exposure. A flash with adjustable power settings would make your life much easier!

Manual mode is harder to use for bounce because you have to take the reflectivity of the surface you are bouncing off into account as well as the total distance traveled by the light. For this a flash meter would be the simplest option.

1) if you want fill flash, then set it to 1 stop less than the ambient. For example, I select an exposure that gives me f5.6 on the lens, then set the flash to f4. You can also try balanced flash where the two numbers match, or even try 1 stop over the ambient for a different effect.

You may want to use a flash meter and see how accurate the sensor is. Mine is off 1 full stop at its f11 setting (only puts out f8).

2) the easiest bounce is from the ceiling, assuming the head swivels up 90°. You can also add a sheet of stiff white paper to the head and force just a bit of the light forward into the eye sockets, which I highly recommend. Otherwise if you are too close to the subject, they can get raccoon eyes.

Street fill-in. Problem for fill flash on the street might be the 1/50 sync speed of your M6; depending on the distance. Example calculation, that you can repeat with your preferred numbers. Assume guide number (GN) 20 @ ISO100, so GN 40 for ISO400 (correct film for street, right?). Assume distance 2m . So flash requires f/20 for nominal exposure (round to f/22); it's fill-in so you want -1stop from nominal, which makes it f/32 for the flash. Now, ambient, sunny16, 400ISO means 1/400s (make that 1/500) at f/16, or 1/125 at f/32. But you can sync only to 1/50! At which shutter speed your fill-in will be not one but two stops below ambient; hardly worth the trouble.

Getting worse if distance >2m. Getting better if your flash is more beefy, like GN 28 @ 100ISO.

Changing from 400ISO to 100ISO will change the aperture from f/32 to a more practical f/16 but will not change the power balance between flash and ambient.

Bottom line: a seventies rangefinder with central (between-the-lens) shutter would be much more appropriate for that exercise. I'd use the flash on Auto, with diaphragm closed one stop from what required by flash (also depends on film speed).

Indoors bounce. I'd use manual mode, bounce off ceiling, compute f-stop according to a fiducial distance of 5m. Then choose shutter speed (no faster than 1/50) according to desired balance of ambient light. Because indoors ambient light is not as strong as in the street case, the balance may be more manageable.

A couple o' things.
1)Does your flash have a cord or just a hot shoe connection? If it doesn't have the ability to point it up or to the side, it's not gonna bounce(unless you throw it real hard).

In years past I've used a thyristor flash simply set on auto and gotten by using it as a direct fill flash. Try it at the f stop on the calculator and one stop down. Check the results & go from there.

All the manufacturers use ISO 100 and 10' as standard for calculating GN. For ISO 100 and a Vivitar 283 the aperture given at 10' is f11. So the GN is 110.

Thanks very much for your quick and very detailed replies. I shoot a lot of Velvia 100 and want to find a way to soften the shadows. This is my reason for wanting to try this flash.

I checked in the manual and found this info.

Guide no:
14 ISO 100 color/m
10 ISO 50 color/m
23 ISO 25 color/ft

Automatic operating range:
Distance 1-3,5m
Aperture f4 for ISO 100 / f2.8 for ISO 50

A weak flash in other words. The flash does have a cable that connects to the M6TTL's terminal below so it can be removed from the hot shoe and still fire (there's no swivel head).

As I understand it, on this flash the difference between the auto and manual modes is only that in auto the flash will cut off the flash when the tyristor senses that enough flash has been provided. In manual mode the cut off is done (so to speak; I mean, from the perspective of the film's exposure) by me by setting the aperture. Would this be approximately right?

It is a bit confusing that there is no way to tell the flash the ISO of the film. I take this to mean that there isn't really an auto mode. The manual says that in auto one follows the orange line in the chart - and presumably ignores the fact that it says distance 3,5 m - but ignoring the distance must mean that the flash will give flawed results at other distances, at least if one uses the flash as main source of illumination (which I am not interested in).



In the street scenario, if I shoot Velvia 100 and the camera's meter tells me the scene is approximately f8 at 1/125 for a correctly exposed photo that would mean f11 at the 1/50 sync speed of the M6TTL (of course, 1/50 is quite slow and risks a bit of blur, but I'm ok with that). So far so good for the ambient exposure.

If I shoot in manual mode and my primary subject is 2m away, then based on GN 14 I should set an aperture of about f7 for correct exposure with the flash as only source. This seems to be what the chart says too; at 1,7m f8 so f7 at 2m seems right. One stop less for fill would mean shooting at f5.6. Now the discrepancy between the ambient exposure's f11 and the flash exposure's f5.6 is two stops. What would happen if I add a 3-stop ND filter? Would I still benefit from the fill flash?

This is making my head spin...Thanks very much for your thoughts
Philip

You are trying to make the flash do things it cannot do.
The auto settings are maximum distances and maximum fstops for that ASA. you may choose a lesser distance or a wider fstop.
Re your street scene. ND filters will not help as they will change both light sources. In manual mode your flash puts out f8 at 1.7 metres. Your one stop less concept is applied to the ambient reading f11 not the flash output of f8. In fact you must only have an ambient reading of f11 ever at 1.7 metres for flash fill of f8

Yes, in this case you don't tell the flash the ISO of the film, it has a fixed light level baked in. You control how much light from the flash hits the film by the aperture you set. A GN for ISO 100 seems weak, until you realize the distance is in meters. 14*3.28 (to convert meters to feet, multiply by 3.28) gives you a GN of 45 in feet, which isn't horrible, but not as good as a Vivitar 283, which I believe has a GN of around 120.

andrew.roos, ParkerSmithPhoto, and bernard_L have already said anything else that I would've said back in posts 2, 3, and 4, so I won't repeat it here. Suffice it to say, they hit the nail on the head.

If you need an upgrade you can pick up a dirt cheap Sunpak Auto-Thyristor on KEH.com. I have two of the AP-52 handle mount models which are great for the street stuff I'm shooting with my Bronica.

philipus said:

I checked in the manual and found this info.

Guide no:
14 ISO 100 color/m
10 ISO 50 color/m
23 ISO 25 color/ft

Automatic operating range:
Distance 1-3,5m
Aperture f4 for ISO 100 / f2.8 for ISO 50

Click to expand...

In other words, the auto mode cuts off when it has seen sufficient light to correctly expose a 100 ISO film at f/4, or a 50 ISO film at f/2.8, which requires the same amount of light. This light level is "baked in" to the flash.

philipus said:

A weak flash in other words. The flash does have a cable that connects to the M6TTL's terminal below so it can be removed from the hot shoe and still fire (there's no swivel head).

Click to expand...

The lack of a swivel head means it will be hard to use for bounce. Even if you remove from the hotshoe and point it at the ceiling, you want the flash's light sensor to be pointed at the subject, not the reflector, to use for bounce flash in auto mode. So you could only bounce in manual mode, which will be a PITA unless yu use a flash meter.

philipus said:

As I understand it, on this flash the difference between the auto and manual modes is only that in auto the flash will cut off the flash when the tyristor senses that enough flash has been provided. In manual mode the cut off is done (so to speak; I mean, from the perspective of the film's exposure) by me by setting the aperture. Would this be approximately right?

Click to expand...

Correct. In manual mode it just flashes at full power. In your original post you mentioned that manual mode is activated by mechanically covering the light sensor This simply prevents it from ever seeing "enough flash".

philipus said:

It is a bit confusing that there is no way to tell the flash the ISO of the film. I take this to mean that there isn't really an auto mode.

Click to expand...

The auto mode cuts off after a certain amount of light has been seen. You can't adjust the cut-off threshold. All you can do is adjust the aperture so that this is the correct amount of light for the film EI/ISO. However this can still effectively compensate for subject distance and reflectivity.

philipus said:

The manual says that in auto one follows the orange line in the chart - and presumably ignores the fact that it says distance 3,5 m - but ignoring the distance must mean that the flash will give flawed results at other distances, at least if one uses the flash as main source of illumination (which I am not interested in).

Click to expand...

3.5m is the maximum distance on auto. It should automatically compensate for closer subject distances by cutting the flash off earlier. Close down the aperture 1-2 stops more for use as fill flash, e.g. by using f/5.6 instead of f/4 for 100 ISO at 3.5m.

philipus said:

In the street scenario, if I shoot Velvia 100 and the camera's meter tells me the scene is approximately f8 at 1/125 for a correctly exposed photo that would mean f11 at the 1/50 sync speed of the M6TTL (of course, 1/50 is quite slow and risks a bit of blur, but I'm ok with that). So far so good for the ambient exposure.

If I shoot in manual mode and my primary subject is 2m away, then based on GN 14 I should set an aperture of about f7 for correct exposure with the flash as only source. This seems to be what the chart says too; at 1,7m f8 so f7 at 2m seems right. One stop less for fill would mean shooting at f5.6. Now the discrepancy between the ambient exposure's f11 and the flash exposure's f5.6 is two stops. What would happen if I add a 3-stop ND filter? Would I still benefit from the fill flash?

Click to expand...

For fill you have to reduce the flash exposure, which means reducing the aperture (i.e. increasing the f-number). So if the flash calculation says f/7, you need to be at about f/11. This happens to be the same as the ambient exposure, so you're good. If the flash exposure and ambient require different apertures, then you may be able to get them to use the same aperture by adjusting your shutter speed, since this affects only the ambient exposure, not the flash exposure. However with the M6 the slow flash sync speed is a real problem - you can't use a shutter speed faster than 1/50" and camera shake means you don't want a shutter speed much slower than 1/50". This is really not a good combo with such an inflexible flash unit. You will find it much easier if you get either a manual flash that allows you to control the output, an auto flash that allows you to program in the camera's aperture (meaning you can adjust the flash to match the aperture required for the ambient exposure; remember to program in that the aperture is one stop larger than it actually is to reduce the flash by 1 EV for fill), or a Leica compatible TTL flash (presuming that either it or the camera has some way to adjust flash exposure comp for fill).

You can't use an ND filter to balance ambient and flash as it will reduce both the flash and the ambient by the same amount, leaving the balance unchanged.

Thank you for the further replies and information. I'm just dipping my proverbial toes into flash photography (sounds rather weird actually) so this is very helpful. Thanks also for the suggestions regarding other flashes with more options. I shall definitely look into those.

There is a rather nice recently-announced Leica flash, the SF-26 which is small, light and has TTL (while it is for the T it works with the M system too, though I'm unsure of the TTL functionality). But at 300€ it's way over-priced given that the original Metz unit is a third of that. Not sure how the Metz version works with other cameras though so that might be wasted money. But these days one shouldn't have to buy a new flash since there are so many old ones around for peanuts.

andrew.roos said:

In other words, the auto mode cuts off when it has seen sufficient light to correctly expose a 100 ISO film at f/4, or a 50 ISO film at f/2.8, which requires the same amount of light. This light level is "baked in" to the flash.
[...]
The auto mode cuts off after a certain amount of light has been seen. You can't adjust the cut-off threshold. All you can do is adjust the aperture so that this is the correct amount of light for the film EI/ISO. However this can still effectively compensate for subject distance and reflectivity.

3.5m is the maximum distance on auto. It should automatically compensate for closer subject distances by cutting the flash off earlier. Close down the aperture 1-2 stops more for use as fill flash, e.g. by using f/5.6 instead of f/4 for 100 ISO at 3.5m.

Click to expand...

Andrew, thank you for this detailed explanation. I will give auto a try when out and about shooting the streets. On bright sunny days, esp in contre-jour situations, the flash may lighten the shadows somewhat, perhaps even without me having to adjust the aperture. I shall experiment.

Again many thanks to all who replied.
Philip