Want to use off Camera Flash with Mamiya 645 pro tl

Hi guys. I normally shoot portrait with my digital pentax, I have some cactus V5 wireless triggers and a manual YN560 flash, which has no auto functions. I use my flash off camera usually through a shoot through umbrella.

What I would really like to do is shoot with my Mamiya 645 pro tl with a similar set up. Now, I have tested the 645 with the cactus V5s, and when mounted to the camera's hotshoe, it triggers the flash. So I can trigger flash wirelessly. The challenge comes when working out how much flash I should be using Vs the camera settings.

Is there an easy way to do this??? I was thinking, maybe I need a lightmeter that measures flash or maybe buy a strobe with an auto function (but would this work through an umbrella??? Probably not!).

Please let me know what you think.

Thanks

Paul

hi paul

do you have a flash meter? that is the easiest way
of determining what settings you should put your flash on ..
or if you know what the output settings are on your flash
( or the little cheat cards that might have come with the flash ) ...
i have a lumedyne kit and it has cards that say 200ws "fx" 8 feet for example ..
( if you know what the settings were on your other camera, with the same iso settings
chances are the settings are going to be similar ... )
is it s thiryster ?
they have an electric eye that will cut your light off when it reaches a certain output ..
my lumedynes now has one of those ... which is great

what flash do you have ?
maybe someone here has the same one, and if you don't know the particulars
( ws, output settings &c ) they can help.

good luck !
john

Years ago I used to use a similar setup for many of my shots, that is a Braun RL515 flash that had only two settings (full power or half), a Reflectasol umbrella and Mamiya C330. I do not remember the guide number of the flash, but assume that it was 160 for this exercise. The guide number of a flash can be calculated by multiplying the known f-stop by the distance. That is, assume it sets to f16 at 10 feet, the guide number would be (16x10), or 160

I knew that the umbrella also lost two f-stops, cutting down the amount of light hitting the subject. You can also calculate this number using your digital camera as a reference.

I position the umbrella with the flash set for full power the same distance away as the camera from the subject. This keeps me from having to do double math. Measure the distance to the subject (assume 8 feet for our example). Then divide the distance into the guide number of the flash (160gn/8ft=f20). Since there is no f20 on my lens, I set it to the closest (f22); which would be the correct f-stop if it were not for the umbrella. Now, knowing that the umbrella will lose 2 f-stops more, I opened the camera up two more f-stops, from f22 to f11.

With your digital Pentax you can check this setup easily, which is what I do before I use my umbrella today. Hope this helps and I did not tell you anything you do not already know.

Wayne

10speeduk said:

YN560 flash, which has no auto functions.

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If your flash is fully manual then there is no difference in operation. You already know how to do it!


Steve.

Flashmeter is the best/easiest option, but you can also preview lighting with a DSLR if you have one handy and don't want to fork out $200-300 for a meter. I use an RZ67 with cactus triggers, Minolta flashes and studio flashes this way.

I've done studio portratit shoot with Mamiya 645Pro and some studio flash.

What you'll have to do first is to setup your lights. Key light and fill light in the position you desire. Then take a light meter and measure the light in both amount and ratio. You can either vary the output or distance to adjust one or both. I used incident method for both. Then, set your camera to 1/60th shutter speed. (that's your max sync unless you are using leaf shutters) Adjust your aperture according to your reading, mostly key.

If you are using speedlight with umbrella, you might not have enough output - depending on setup.

I use off-camera, manually controlled flash with Cactus triggers and my Bronica ETR setup.

The most reliable way to work is with a flash meter that has a PC sync plug. I use a Sekonic 328 with an incident bulb. The Cactus transmitter is plugged into it, and I go to the model's position and can wirelessly trigger the flashes and take a reading all at once. It works very quickly this way -- the only slowdown is switching the transmitter back to the camera. I have thought of getting an additional transmitter so I can keep one on the camera and one on the flashmeter.

First up, thanks to everyone for your replies, this is an amazing forum -you lot certainly have a great deal of knowledge and skill! I am really tempted to buy a tempted but I am really intrigued to try Wayne's solution first:

Too old to care said:

I do not remember the guide number of the flash, but assume that it was 160 for this exercise. The guide number of a flash can be calculated by multiplying the known f-stop by the distance. That is, assume it sets to f16 at 10 feet, the guide number would be (16x10), or 160

I knew that the umbrella also lost two f-stops, cutting down the amount of light hitting the subject. You can also calculate this number using your digital camera as a reference.

I position the umbrella with the flash set for full power the same distance away as the camera from the subject. This keeps me from having to do double math. Measure the distance to the subject (assume 8 feet for our example). Then divide the distance into the guide number of the flash (160gn/8ft=f20). Since there is no f20 on my lens, I set it to the closest (f22); which would be the correct f-stop if it were not for the umbrella. Now, knowing that the umbrella will lose 2 f-stops more, I opened the camera up two more f-stops, from f22 to f11.

With your digital Pentax you can check this setup easily, which is what I do before I use my umbrella today. Hope this helps and I did not tell you anything you do not already know.
Wayne

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I have checked my flash which is a YN560 (http://www.hkyongnuo.com/e-detail.php?ID=275) it says the guide number is 58 at ISO100. So just to check I have got this correct, assuming I have ISO100 film in my camera and I run my flash on full power, and both camera and flash are set equidistant from the subject, say my subject is 5 feet away. Then divide the GN of 58/5ft = 11.6; F11, then lose 2 stops for the shoot through (approx) = F5.6. I also assume that due to the speed of the flash Vs the max shutter speed of 160s (I am using std 80mm 2.8 lens) that the shutter speed cannot influence the flash exposure and therefore does not figure in the calculation (obvs, it does affect ambient exposure)?

Also if I am correct, if I open my aperture to F4 (with the above example), I can reduce my flash to 1/2 power? And if I use ISO400 film, does this effectively multiply my guide number by the power of 4? So 58x2 =116x2 =232...brain is flickering now!??!!

Please let me know if I am in the ball park here! Cheers again, Paul

Ps, I would love to see some film/flash studio portraits if anyone would care to indulge me!

Almost everything in the first part of you question is correct, if your umbrella looses 2 f-stops. However, each reflective (transparent) surface is different, thus may have different losses. You should be able to find this out in the literature, or experiment using your digital camera. My umbrella looses 2 f-stops on one side (flat silver) and 1 f-stop on the other (shinny silver). Another other detail is the ambient light. If you are shooting in strong light you may have to further reduce the exposure. I used to shoot weddings, so this was not the issue since most were at night. When in doubt, I used to also set my shutter to 1/500 of a second to reduce ambient light problems. You can do that with a C330 and the flash still works. You will have to experiment here to see what works best.

On the second half you are partially correct. Remember, guide number is calculated by multiplying distance by f-stop, not ISO. 1/2 power is the same as cutting the guide number enough to lose one f-stop. To make math easier, say the distance is 10 feet (I should have used that anyway to keep the math simple instead of 8 feet). In my new example this would reduce the guide number from 160 to 110 (110gn/10ft=f11), which is one f-stop down from f16.

Next. Using ISO 400 instead of 100 does not increase the guide number by 4 f-stops, only 2. Assume that the gn is 160 and distance is 10 feet at ISO 400, the f-stop would be f16 (160gn/10ft=f16). Now we drop the ISO to 100 so we need to increase exposure by 2 f-stops, or to f8. The new guide number would be 80 (80gn/10ft=f8). Again, remember guide number is distance multiplied by the f-stop, ISO does not enter into the equation. The guide number will be different for each ISO, just do not confuse the two.

Hope this helps more,

Wayne

Too old to care said:

Almost everything in the first part of you question is correct, if your umbrella looses 2 f-stops. However, each reflective (transparent) surface is different, thus may have different losses. You should be able to find this out in the literature, or experiment using your digital camera. My umbrella looses 2 f-stops on one side (flat silver) and 1 f-stop on the other (shinny silver). Another other detail is the ambient light. If you are shooting in strong light you may have to further reduce the exposure. I used to shoot weddings, so this was not the issue since most were at night. When in doubt, I used to also set my shutter to 1/500 of a second to reduce ambient light problems. You can do that with a C330 and the flash still works. You will have to experiment here to see what works best.

On the second half you are partially correct. Remember, guide number is calculated by multiplying distance by f-stop, not ISO. 1/2 power is the same as cutting the guide number enough to lose one f-stop. To make math easier, say the distance is 10 feet (I should have used that anyway to keep the math simple instead of 8 feet). In my new example this would reduce the guide number from 160 to 110 (110gn/10ft=f11), which is one f-stop down from f16.

Next. Using ISO 400 instead of 100 does not increase the guide number by 4 f-stops, only 2. Assume that the gn is 160 and distance is 10 feet at ISO 400, the f-stop would be f16 (160gn/10ft=f16). Now we drop the ISO to 100 so we need to increase exposure by 2 f-stops, or to f8. The new guide number would be 80 (80gn/10ft=f8). Again, remember guide number is distance multiplied by the f-stop, ISO does not enter into the equation. The guide number will be different for each ISO, just do not confuse the two.

Hope this helps more,

Wayne

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Thanks Wayne, I think I am nearly there (!). Just to confirm when you say f-stop, you mean my lens aperture? The manufacturer of my flash says the guide number is 58 at ISO 100, I do not know what this actually means, are you saying I should disregard this? So lets say I am set at 10 feet from my subject for flash and camera. I have set my aperture at f4, so my guide number is 40? Erm, I think I am truly confused. sorry!

f-stop is aperture. Each f-stop cuts exposure by 50% when you go up, and doubles exposure when you go down. Example, f4 lets in twice as much light as f5.6. And in reverse f5.6 lets in 1/2 as much light as f4. This is why your shutter speeds are either double the previous one, or 1/2 the other one, depending upon which way you are going. So, at f5.6 and 1/60 of a second, you would have the same amount of light hitting the film as at f4 at 1/125 of a second. Drop the f-stop by one double the light, cut the shutter speed by one and 1/2 the light, even trade.

Do not disregard the guide number given by the manufacturer. However, if you do not know it you can calculate it by multiplying the f-stop by distance. I use 10 feet because the math is easy. Example, assume that you have a guide number of 160, that is 10 feet times f16. Or, 14.5 feet at f11 (14.5ft x f11) which is still 160, or 20 feet at f8 (20ft x f8) which is again still 160. The guide number stays constant only with the ISO, not the distance or f-stop. That is how you calculate the f-stop based upon the distance. Just divide the distance into the guide number for the f-stop. Many strobes have a calculator built in.

This is the one on my current flash, Sunpak 544.

You need to know if your guide number is in feet or metres. At 58 I think it's safe to assume it's feet. You also need to know at what ISO this is rated at - it is usually 100.

For a subject 10 feet away, dividing the guide number by distance = 58/10 = 5.8.

The closest aperture is 5.6 which will work fine at ISO 100.


Steve.

Steve is correct, in my photo above the guide number for the flash at ISO 800 would be 40 if measured in meters, or about 140 if measured in feet. (10 meters x f4 = 40 guide number in meters) (35 feet x f4 =140 guide number in feet) Again, this is only for ISO 800. Moving the ISO dial would change everything and give a new guide number. If I did not have this calculator you can still do it in your head.

At 58 I would assume (hope!) it's in metres - I have a couple similar-sized Minolta flashes (5600) that are 56m at ISO100 at full zoom (80mm). If it's 58 feet, it's a totally pissweak flash that's not worth using for medium format and there is no way it will give enough light. For a constant beam pattern, a flash with 56m GN has 9x (more than 3 stops!) more power than a flash with 56' GN.

Anyway, Guide Numbers are useful only for calculating exposure when directly illuminated by the flash; they are not useful for calculating exposure through a light modifier like an umbrella or softbox. The reason is that the GN tells you the angular flux density of light, i.e. number of photons passing through a particular subject area and therefore (when divided by distance) give you a measure of the light intensity falling on your subject. They do not tell you the total number of photons available (net flux, generally measured using electrical Ws = J as a proxy), which is what you need to know when using a modifier.

Note that they quote GN at maximum zoom on the flash, i.e. with a very narrow beam. If you widen the beam (zoom the flash out), the GN reduces dramatically because the beam has been spread out and dimmed. You therefore cannot compare flash powers using GN unless you know that the beamwidths are very similar. Say you're doing a direct flash exposure; test it with the flash zoomed in and zoomed out and with manual power; note that there's a couple stops difference in achieved intensity due to changes in beam spread.

When you put a flash in an umbrella, what matters is the total photon flux (total energy) from the flash. Ideally you want to spread that over the whole umbrella surface for even lighting, but for exposure purposes, it doesn't matter much if it's in a tight, bright beam (flash zoomed in, high GN) or a broad dim beam (flash zoomed out, low GN). And then, the modifier itself will absorb some light. They all absorb a different amount depending on construction and materials used.

Short answer is, you cannot guess an exposure through a modifier based on the GN. For sure you can guess the exposure once you've measured the light using your particular flash and your particular modifier and know how it behaves, but you can't compute it from the GN. For example, I know I can get about f/18 at 1m with my 600x600 softbox and a Minolta 5600... but I only know that because I measured it.

The next thing that's going to confound your guessing is that a light modifier by its very nature is a large light-source (otherwise why bother?) not a point source, therefore it does not obey the inverse square rule when it's close to the subject.

Get a flash meter, or preview your exposures in M mode on a DSLR. Both options will give you accurate exposures. Guessing will not unless you have experience obtained with a meter and your equipment, guessing ab initio from GN will get it completely wrong.

polyglot said:

Note that they quote GN at maximum zoom on the flash, i.e. with a very narrow beam. If you widen the beam (zoom the flash out), the GN reduces dramatically because the beam has been spread out and dimmed. You therefore cannot compare flash powers using GN unless you know that the beamwidths are very similar. Say you're doing a direct flash exposure; test it with the flash zoomed in and zoomed out and with manual power; note that there's a couple stops difference in achieved intensity due to changes in beam spread.

Click to expand...

Yep, something they will mention just be sure you have your eyeglasses prescription up to date

polyglot said:

Get a flash meter, or preview your exposures in M mode on a DSLR. Both options will give you accurate exposures. Guessing will not unless you have experience obtained with a meter and your equipment, guessing ab initio from GN will get it completely wrong.

Click to expand...

A good flashmeter is indispensable imo.
I did learn guide numbers but one of the VERY first accessories I bought was a Sekonic L358 because I was learning in a studio environment as well as shooting in natural light.

Both answers of the last two replies are true, but I disagree with not using GN if you also know the amount of light lost by the umbrella, it is simple math. When I started shooting weddings in the 60's for a living, before becoming an electrical engineer, this is all I had to work with and it worked quite well for the 12 years I was a full-time professional photographer, first working part time for two studios, later owning my own company. When I started I could not afford the flash meters available at the time and I had to learn how to use my equipment instead of relying on expensive equipment that I did not own. I am only trying to teach a technique that I have used for 1/2 of a century. Man, does that make me sound old!!!!!

Wayne

TOTC: while I'm sure you knew your equipment well (i.e. you knew the effective GN of the brolly output with your flash) and could use this technique reliably to judge flash power based on brolly/subject distance, it's not going to work for a beginner who is sticking an unknown flash into a softbox for the first time and hoping to compute the exposure using some rules of thumb.

The point I'm trying to make is, "GN and flash power are not well related". For a softbox or umbrella, what matters is the total power of the flash whereas GN specifies how bright the beam is and there is a very fuzzy relationship between the two that differs quite a lot between models of flash and their beam patterns. For example, my Minolta 5600HS(D) is rated as 56m and the Sigma 500EX is rated as 53m. However, the former has a broader beam, the latter has a narrower beam and about half the output power of the former, though the GN (intensity within the beam) is nearly the same. Therefore a GN-based calculation that will work with my Minolta flash will give a stop of underexposure using the Sigma and vice-versa.

To the OP... if you're being totally cheap, you can of course use some film (preferably chromes because of their high contrast; Velvia 50 will be the most stringent test) as a light meter. Take a well-exposed reference shot of a diffuse item (e.g non-glossy plastic toy) in Sunny-16 lighting (ISO50, 1/125, f/10 or ISO100, 1/125, f/14), setup your brolly exactly 2m from the subject and take a series of shots aperture-bracketed at 1/2 stop using your flash. One of them should match the reference pretty closely and from that, you can work out an approximate GN of your softbox.

polyglot said:

At 58 I would assume (hope!) it's in metres.

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You could be right - I don't know the flash being referred to. 58 metres would be 190 feet.

As long as you know what unit is being used the calculation will work.


Steve.

Now we agree on a technique. But instead of burning film, use your DSLR set to a fixed ISO, shutter speed and f-stop on manual, and make some test shots using the histogram to find the effect guild number of your umbrella and flash.

One of the most import things I learned decades ago was the relationship between ISO, f-stop, shutter speeds, and the amount of light lost due to distance of camera/flash to the subject. Once you experiment to find the right combination it is just a mater of simple math to change one variable.

I learned as an apprentice working at my first job. It really is simple, although it sounds complicated. Hope this helps,

Wayne

Wayne, Steve and Polyglot, thanks for explaining this. I get it now

I think I will experiment by testing the maths calculation Vs my DSLR (I only have one umbrella and one flash) then approximate the loss through the umbrella. Will let you know how I get on. Thanks for all your wisdom!!!!!!!!

Cheers

Paul

10speeduk said:

I think I will experiment by testing the maths calculation Vs my DSLR

Click to expand...

That's no different from what people used to do using Polaroid for test shots. A lot cheaper with a DSLR though!


Steve.

polyglot said:

At 58 I would assume (hope!) it's in metres - I have a couple similar-sized Minolta flashes (5600) that are 56m at ISO100 at full zoom (80mm). If it's 58 feet, it's a totally pissweak flash that's not worth using for medium format and there is no way it will give enough light. For a constant beam pattern, a flash with 56m GN has 9x (more than 3 stops!) more power than a flash with 56' GN.

Click to expand...

58m pissweak? On earth?
Vivitar 28X gives a GN110 with ISO 100 and 22m in meters and many use the series with MF cameras. Oh well, YMMV.

Anyway back in the olden days most references would tell a fledgling flasher to do the following.
a)Measure or step off 10 feet and place your subject there.
b)Give your subject a SERIES of cards with apertures written on them in sequence. 1/2 stop will be more accurate.
c)Make an exposure at each f stop marked on the card
d)Process the film. The GN of your flash is the one that is properly exposed. At ISO100 If 5.6 is correct, multiply by 10(feet) that equals GN56.
@ f11 the GN is 110.
This gives a base for ISO 100 @ 10 feet and different distances can be calculated from that.

TOTC is doing the same calculation using the aperture as his base. Ya does what's comfy 's all.

John Koehrer said:

58m pissweak? On earth?
Vivitar 28X gives a GN110 with ISO 100 and 22m in meters and many use the series with MF cameras. Oh well, YMMV.

Click to expand...

58 feet is pissweak and completely unsuitable for bounce-lighting (or use in a softbox/brolly) for medium format. It being 1/9th of the power of a 58m flash, which is moderately useful (modulo the beamspread it's quoted at) for medium format.

Note that with GN=110 feet, there's four times the power as with GN=55 feet.