Thursday, September 23, 2010

Raw Power

This picture was taken mid afternoon in Dubai, with the sun about half high in the sky. The flash power needed in this circumstances is no mean feat, if an umbrella is used. The aperture was relatively open at 6.3 because I used a Polarizer to soak up light and smoothen the skin tones. The main light comes from a shoot through umbrella with three Metz 45 at manual full power. The fill light was an on camera SB 900 set to manual 1/32 which also triggered the Metz Set up.

The three flashes assembled with their brackets. All of them had the diffuser on, and were set to full Manual Output.

I used three photocells to trigger them individually, because I used three different models. CT-1, CT-4 and CL-4 digital. I did not want the three different models with very different Voltages to be wired together. Therefore one cell for each.
!!!! Caution !!!! If you connect a CT-1 and a low voltage model to the same cell electronics might be damaged!

The main question I want to explore today is the one of multiple flashes used to get a stronger output. Joe Mc Nally's Christmas Tree like set up with many SB-800 and SB-900 are legendary.
However there is physics to be considered. Combining two flashes does NOT result in double the guide number. Because light fall off in square relation to distance one needs a the power of 2 of number of flashes. Therefore to double the guide number (effectively double the distance)  FOUR units are needed. To quadruple the guide number SIXTEEN units are needed.

There is a German website which has a number of tools to easy calculate some photographic relations. On the bottom of the page is a tool where one can give in the guide number of combined flashes and the overall guide number is calculated.

Below is a table with Guide Numbers for additional flash units used. (Guide Number for ISO 100 in meters at 35 mm)
Flashes SB 800 SB 900 Metz 45

Looking at the table there are a few interesting observations.
1) For each additional unit added the actual increase in guide number gets less and less. The second SB 800 adds 16 to the overall guide number. The eighth adds only 6. The conclusion is that the "many small light" build up has its limitations and the point where it becomes really impractical is quickly reached.
2) Comparing models in the table one realises that maximum initial power is desirable in such a set up. For a guide number of 90 one needs 4 Metz 45ers compared to 7 SB900.
3) Big Stobes are really more practical from a point. 500 Ws = GN 85, 1000 Ws = GN 120, 1500 = GN 150. Comparing price and bulk the big ones are worth a consideration if a high power light output is needed. To replace one 1500 Ws big flash 16 SB900es would be needed.
Huh? Isn't that contrary to the whole carry less equipment story that started the strobist movement?
Well a full fledged big flash set up with 2 to 3 lights is much more bulkier than 3 or even 8 small flashes. The many small flashes are also more versatile in distributing them. And most of the time when full power output is not needed the small flashes do the same job as a big one with a weight advantage comparing light to light.
However when Raw power is needed the big ones come to the forefront.
Back to the picture above. The three Metz 45 have a raw GN of 78. With 200 ISO , 1.7 meter distance that would amount to an Aperture 64. The light loss in the shoot throough umbrella of roughly two stops brings us to Aperture 22. A further two stops of loss for the polarizer and we arrive at 11. The wide angle diffusers bring us to about 8. Close enough to the aperture found by test shots.
The sky is in the direction against the sun and is still very, very bright. Closing the aperture further to get the sky darker would have needed quite a bit more light.
So how far can I go by using all my available flash units fired together? 2 x SB900, 4x SB800, 2 x Metz 54-4, 6 x Metz 45 Total =152 I have not tried that yet. There will be another sunny weekend in Dubai.

Saturday, September 11, 2010

Batteries or Rechargeable

The intro picture has nothing to do with today's experiment except that I used batteries in the SB 900. Normally one tries to avoid a sharp shadow from the flash but in this picture I wanted the shadow to repeat the form of the sculpture on the little tower. The picture was taken in the castle of Gruyere/Switzerland . The sculpture is from the artist HAFIS. The old White balance and gel the flash technique is much stronger here due to the rusty surface.

Now back to on topic: The Metz 45ers get their power from one of three sources: A battery cage or a rechargeable pack that are inserted in the bottom of the grip, or and external battery pack.
Today we look at the internal sources only and ignore the external packs for the time being.

The flashes are delivered either with a battery cage to be filled with 6 AA (or mignon) cells. Some versions are delivered with a Metz rechargeable pack where 6 rechargeable cells are in a pack cage and a dedicated recharger. The individual rechargeable cells of the rechargeable pack can normally not be changed or taken out by the user.

Now we all know that the old NiCD rechargeables are a pain in the ass. They need constant fussing about, care and maintenance to work properly. So they have not been very practical for anyone without a full time assisitant, to whom to delegate charging and de-charging the packs once in a while and re-charing them at the right time. Whenever you wanted to do some shots at the spur of the moment the packs were not fully charged. Charging on top of the current charge provoked memory effect, which had to be healed later with days of charging and uncharging.
A complete un-charging and re-charging took 4 hours at best.

For most hobbyists the rechargebale pack went inbto the closet and the flash was operated with batteries in the battery cage. 2000% less hassle.

Later the NiMH rechargeables and the eneloops (like NiMH but hold the charge longer) came to market which made life a lot easier. Many people used a electronic charger like from Ansmann with 6 loading bays and one or two sets of NiMH or eneloops and popped them into the battery cage and went from there.

However (there seems to be always a however) the flash units have 3 pins in the power bay and the connection pins from the battery cage and the rechargeable pack are different.

There has been endless debate in many forums if it makes a difference in practice to put your rechargeables into a battery cage. Some people have posted nice instructions on their blogs how to dissect an old Metz Rechargebale pack with NiCd cells and replace them with Eneloops. Of course that has the drawback that you will habce to get a new charger as well, and it needs to be a charger that can charge the cells when they are connected in a row together (in the pack).

One nearly spooky aspect of Metz as a company is their efficient customer service. Ask any question on their website and you will receive an answer normally within two business days that not only answers your question but also some taht might be connected and for good measure throws in all manuals in pdf of all parts that were mentioned. I don't know how they keep up that stellar performance in this day and age, but way to go Metz!

The customer service is cited of explaining that older models suffer from less power, when rechargeables are used in the battery cage, newer models have a new electronic and it doesn't matter anymore. Still many posters in the forums insist that they do not see a difference in practice.

The reason for the two seemingly contradictory statements is simple. As explained earlier, one of the big advantages of automatic flash is, that the "unused" power is stored for the next shot. So if you have a realtively large aperture like 4 or 2.8 and shoot in Automatic or TTL mode, the flash might only use 20% to 50% of its power depending on distance and subject. So if the "fully" loaded flash has only 95% instead of 100% power, one might never notice.

However I intend to do experiments later on where we test limits of automatic flash and compare the 45ers to the modern hardware, I would like to know, if there is a difference in the flashes I own and how much is the difference.

And that brings us to today's experiment:

Three battery cages with: left fresh batteries, middle NiMH freshly re-charged, but well used and on the right the new NiMH recently bought and charged and no longer fully charged. Kind of a usual mix that can be found in any Hobby Strobist's bag.

Not in the picture but also used is a Metz NiMH pack (from 2009).

First I determined the current voltage of all packs:

The batteries gave 9.5V which is 6x 1.6 not unusual for fresh out of the pack.

The older NiMH gave 8.1V which is 6x1.35 again higher than nominal but not unusual fully charged.

The newer NiMH gave 7.85V which is 6x1.31, still well above nominal.

The Metz Pack gave also 8.1. Notice the difference in contact pins.

The set up is as follows:

- I tested three different flash types 45 CT5, a 45 CT4 and the newest 45 CL4 digital.

- The flashes were connected to my D300s (all of them are safe, I measured the trigger voltage) shooting a corner of a room. The motive is a grey felt cloth clipped to a light stand.

-Each flash is fired with full power in manual mode, the output is measured by a Gossen Lunasix used as flash meter.

-Ambient light is very low, curtains are drawn. The ambient light measurement would have been 1/4 second at f4 as determined by the camera.

- The camera is set to 1/60 and f/11 as determined by a flash meter reading, which is 7 stops above ambient level. A test shot without flash at this setting is completely dark (not shown)

- The camera and the light meter are set to ISO 200.

- Absolutely unnecessary as we will shoot full manual the flashes are also set to ISO 200. Just for fun.

The camera and flash (in this example 45 CT5) looked like this:

I like the display on the 45 CT5. If it is on a tripod it might not be easy to look on top. It is nice to see on the backside what has been set by wheel on top.

Test 1 45 CT5

Flash meter reads 16.1 which is f16 and a 1/10 stop

(The Gossen measures in 1/10 of a stop and gives a decimal reading)

The New NiMH (eneloop type) noticable darker.

Flash meter reads 11.6
Oha! that is a half stop less!

The usual NiMH type.

The flash meter reads 11.7.

As expected nearly same result. 0.1 stop difference is within tolerance.

Test 2 45 CT4

Despite the lower number a newer model that replaced the CT5. Basically the same result. I do not repeat the pictures.

Test 3 45 CL4 digital

All variations I tried including the newer Metz recharge pack and an old Metz recharge pack produced the same result.

They did really improve the electronics quite bit!

The meter read in all instances exactly 16.9. The 0.8 difference to the first shot above come from the fact that I used the wide angle adapter on the first two flashes and not on the CL4 digital.


1) The current models like CL4 digital don't care what voltage is delivered and always deliver constant output including maximum output.

2) The older models deliver around 0.5 stops less maximum power when rechargeables are used in the battery cage. more so there seem to be slight variations in maximum power depending on the actual voltage of the power source.

3) The wide angle reflector causes a drop of 0.8 stops maximum power. (the manual says 1 stop)

Open questions:

Which models are exactly with the new cool electronics?
When using automatic how much do I have to deduct from the maximum distance indicated when using rechargeables?

Answers soon

Tuesday, September 7, 2010

Back after the Summer Break

Many factors contributed to me having a blogging break during summer.

The biggest contributor was definitely the Dubai summer heat , as most of my experiments would require to be outside to have enough space. But there has also been a general lack of time and the annual vacation. Now the Eid al Fitter is here, temperatures have moderated a bit and I acquired some more second hand toys to play with. All a good combination to call the official end of the blogging break.

In this small season opener I want to repeat what the blog is about, what is the general plan and where we are:

The highly developed external flashes that are state of the art today include a multidude of settings and modes how to operate them. This technical diversity might be confusing to anyone, who has not followed the development of flash technology and techniques over the last 30 years.

I will look into each layer of the technical development and make some experiments to explain and see how they work. At the end we all might have a better understanding of the many current possible settings, their advantages and disadvantages.

From time to time I will also post a general flash related post, or if I made an observation regarding current equipment.

So far in the blog I

and (here).

The grand plan to continue the Blog is:

- finish the experiments with automatic flash and the Metz 45 family

- remote set up with automatic flash

- (Film based, "simple") TTL

- look at the different "advanced" TTL methods

- remote set up with "advanced" TTL

- "mixed" remote set up

The immediate upcomming installments will deal with automatic flash and the Metz 45 Family as laid out before the summer break:

- A number of experiments with automatic flash- comparing it to the modern marvels.
- Finish the introductions of the flash accessories.
- A number of experiments wit the flash accessories.
- An overview of the 45 family then and now.
- Experiments with a set up of multiple remote controlled automatic flashes.

From time to time I will also just throw in some flash pictures as they come along.

During the holiday back home I shot the followwing three with the SB-900 that accompanied me in the small kit. (I consider one fully grown flash essential and will rather leave a lens at home instead.)

1/4 second, f4, ISO 800, no flash

The first shot shows the ambient light shortly after sun set.
The ambient light is quite blue in nature and only the street lantern give a more warmer light to their lightened up area.

I thought how it would look like to get some light into the trees.

1/4 second, f4, ISO 800, flash

The second shot has the flash in the hot shoe turned on. Mainly the street in front of me is lightened up the trees are still quite dark.

1/4 second, f4, ISO 800, flash swiveled 45 degrees up.

What a funny light pattern on the street! Look at how even the tree on the right gets some light.


More Swivel - More Fun!