Yoshizen's Blog

Ring Flash / Flash Story

Ring-flash on Fisheye(B)455

——– (This Ring Flash was made to use with the Fish-eye lens on the

——– Yoshi-handy handmade camera, 36 years ago !  😀 ) 

In some posts ago,  I’ve shown Studio Flash and ring Flash tube.  

May be I should talk a bit more about Electronic Flash-light. — Why It’s called “Electronic

Flash” was, before, Flash-light meant Bulb Flash = the people over 60 might remember,

even if it was not a typical bulb shape, how about Flash-cube / Magicube at the time of

Kodak Instamatic camera, they are still flash bulb, but only small.  🙂

Flash bulb was an “Explosive device” = thin aluminium foil was packed into a glass bulb

with Oxygen and ignited by an electric spark, with a “Bong” noise !  

( I only know from Antic collection though, yet before  Flash bulb, it was an explosive 

magnesium powder = it’s literally explode ! —– hence, all the assistant of a photographer

used to have a lots of spot on their face, burnt by the exploding magnesium powder.  😀)

  []  

Unlike such hot staffs, electronic flash is using a discharge of high voltage electric energy

through a Xenon gas filled tube.  To make this, a capacitor inside of a Flash was slowly

charged-up to high voltage, then discharge it in an instant to produce very intense bright light.  

Like an electric spark, it needs to be high voltage, and the larger the capacitor,  

the light produced from it would be the brighter.  

This is the reason why a camera’s built-in flash, which got only small capacitor inside, was

not bright-enough to reach distance.             In contrast, a studio type big Flash having a bank of

Bank of Capacitors A09A0669

capacitors connected parallel to store huge energy, 

and the big flash tube was made by a quartz to

withstand the heat shock created by a

discharge of huge energy.  

And to charge-up those capacitors, studio type is

using the main electricity and a

portable type, clip-on type are using electronic

voltage converter to rise the battery voltage

to 315 ~ 350 V.  

[]

Capacitors A09A0667

As I said, the electric energy is first charged into

the capacitor.  

The capacitor is an electric device, which was

made by insulated two metal plates or foils

to store electric charge.  In order to store as much

as energy, very thin two aluminium foils were

tightly wound together.    And to separate two

metal foils, paper or plastic film ect. which called 

dielectric material was sandwiched between.  

But most of the capacitor used in a flash equipment is a

type called Electrolytic capacitor which is not using common insulator, hence smaller in size.

   []

It is not well known to the people that those Electrolytic Capacitor has a limited life.  

Especially if the equipment was not used long time (more than a year) they might be dead

and a moment when it was switched on again after long rasp of the time, the capacitor

would be internally short-circuited and gone for ever. —– ?   Why the insulation breaks ?

[]

If you tested the conductivity of Aluminium, you may know, despite the Aluminium is a

very good conductor,  Anodised surface shows no conductivity.   With the Anodisation,

the surface  of Aluminium was covered with the aluminium oxide which is an insulator.

Instead to use a separate insulator between two Aluminium foil,  Electrolytic Capacitor

is using this oxide coating developed own surface as a dielectric / insulator.  

So that, as long as the capacitor was kept receiving electric current, they maintain

the oxidized coating on the surface of aluminium foil.   But if the equipment was left

unused long time, the insulative coating deteriorate.

—– And a moment when it was switched on again, and the voltage rose high,  the

insulation breaks down and makes two foils short-circuited and start to generates heat,

or the power transistor pumping the high voltage into the capacitor burns-out.  

If the capacitor over heat  it would explode.   (In fact, the situation is always the same

where ever electrolytic capacitor was used — such as even an audio power amp.)

  []

The remedy to this situation is, the same as to initialise a capacitor in a factory.  

= slowly charge up the capacitor while waiting the insulating coat grows on the

surface of the aluminium foil (in its anode-side, hence it called Anodisation.)

—– To do this, professional people use variable transformer (Rheostat) and sloooowly 

rise the voltage while giving hours of time.  

(If you try, — You need to constantly measure the voltage of the capacitor —– first

second or two of switch-on, when you see the voltage rise to 5~10 V, then switch-off — if

the voltage shows “slowly” dropping, switch on again to see it reach to 15 V —- then

switch-off and wait till it’s drop to 10 V and switch on to 20 V again (like two step

forward, one step back) —— in this way until it reached to more than 300 V then to

the full —– all the process will takes hours !   🙂  or 😦  

 —– But if you see the voltage drops rather quick, and  never rise above

the certain voltage, don’t push it further, and you have to

accept that the capacitor is already dead !  —– Sorry about  😦  

(still better than to see it exploded in messy manner.)

  []

In another approach, if the capacitor could be disconnected from the charging circuit.  

(But this is only for the experienced person.) —– Use the main AC power.  

Connect a Rectifier to live, and 100 K (may be reduced to 50 K, 10 K on the later stage)

register to neutral.   And use this rectified direct current to charge up the capacitor.  

In the first few seconds, when the capacitor’s voltage  rose to 10 V, then disconnect.  

When voltage was dropped to 5 V then charge it to 15 V (Keep a distance of up and

down proportional  —– repeat this again and again, while time to time having a break

(to have a cup of tea  🙂 and make a capacitor to regain a potential to charge-up to

higher voltage) and slowly bring the voltage to the full.  

From the main voltage in Europe, rectified voltage would be 310 ~ 330 V, about the

same voltage of the working flash.  But in the US  110 V, it’s needs  to use voltage

doubler circuit.   And a fully charged capacitor of 1000 microF, 2000 microF has an

energy to evaporate a tip of screw-driver, if it was short circuited — and hell like Bang!  

= Before you do any  work, always DO NOT FORGET to discharge the capacitor

through 5W 1K register.

(If you couldn’t understand  what I’m talking here straight, DO NOT attempt to try this !

—– to touch AC main, 200, 300 V DC is killingly dangerous for amateur !  

(Accident happens in a completely unexpected moment, in an unexpected situation.)

  []  

Assuming the capacitor is working perfect, the rest of the flash circuit is rather simple.

The thick two cables from capacitor were connected to the both end of a flash tube.  

And an additional cable was attached outside of flash tube = this is the trigger which

receives 3000 V or higher voltage pulse. —– To trigger this very high voltage pulse, a switch

inside of camera shutter-mechanism used to short circuit a small capacitor in the primary

side of trigger coil, then in the  secondary side 3000 ~4000 V pulse will be produced.    

But now-a-day, sophisticated electronic camera can not take such high voltage, —– instead,

a trigger to flash was done by low-voltage signal.  

= (In another word, to connect very old flash to a modern DSLR is highly risky.  

(If you got Test Meter, you can measure how high the trigger voltage of the flash, on the

connector of  Flash extension cable.  If it shows more than 15 V, (it could be as high as 100 V),  

never use it direct to the camera = Use a Slave trigger.)

  []

Once you understood the structure of flash-light, to modify it, is not very difficult.  

My Ring flash on the photo was made to take the power from Brown F900 power pack

but before it was connected to Kako hummer-head flash.   As long as it receives 300 ~ 350 V,

it will flash and the light-intensity is depend on the size of the capacitor.  

(By the way, Flash-tube’s life is also limited !  = Don’t expect it works for ever.  😀 )

(That Ring Flash Tube can take, up to  200 WS = C x V-square x 1/2 = Wat-Second

such as—–1000 microFarad x 315V x 315V x  1/2 = 50 WS = GN may be about 25~28  though

it’s all depends on the efficiency, size of the reflector, how old the tube is, etc. etc.)

[] 

Advertisements

6 Responses

Subscribe to comments with RSS.

  1. elenacaravela said, on September 4, 2013 at 14:22

    Wow!

  2. Lemony (Gr)Egghead said, on September 4, 2013 at 20:09

    That is a very involved project. 🙂

    • yoshizen said, on September 4, 2013 at 20:47

      I always push it to the extreme. —– otherwise what’s
      the point to DO it or live. This is the Zen.

  3. I have read a few good stuff here. Definitely worth bookmarking for revisiting.
    I surprise how much effort you set to make any such wonderful informative website.

    • yoshizen said, on June 1, 2014 at 20:07

      Thank you very much to visit here.
      —– It was not much of effort, simply I’ve been
      dealing with them long time, and I’m actuary doing, making them. = it’s not just a knowledge from the paper.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: