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Photography Question 
Howard 
 

built in flash Minolta Maxxum ST/SI QD.


How do I get my 35mmMinolta Maxxum ST/SI to flash continuously without having to wait 10 or more seconds to charge?


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6/13/2002 8:49:45 PM

 
Ken Pang   You can actually build a bank of capacitors, charging from a large belt clip of batteries. It depends on how much power your flash uses, and how quickly you draw power, but I would say that 10 capacitors in a round robin order, should give you one frame per second continously, until the batteries die down.

Seriously? Get an external flash... Internal flashes are hopeless for fire rate. Also, 10 seconds is long - even for an internal. Try replacing the batteries with something that can give higher current, without giving higher potential difference. (Higher milliamps, same voltage). Something like the titanium batteries, or at the least, lithium ones.


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6/13/2002 9:25:45 PM

 
Howard    Dear Ken P.

I am already using CR2 batteries in my camera. How does an external flash have to do with firing the flash continuously?

I plan to do get an external flash eventually after taking an 8 week beginners course at a community school in Pembroke Pines, Florida.


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6/15/2002 1:35:08 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Howard,
The amount of light put out by a flash under "auto" control is not by brightness, but by duration. It's so short that you can hardly tell the difference. This is teh case whether it's by the camera body or through a sensor on the flash itself.

The built-in flashes are notoriously low power with very low guide numbers (abbr. GN). This means they must do a "full dump" of all the light they can put out for nearly every flash use. The result is a long recovery time.

An external one with a GN over 100, especially those around 120 and higher, can recover faster because they're doing partial dumps nearly all the time. For things such as wedding receptions that are in cavernous halls with working distances often twice that encountered in the average home, I use an even higher flash power with a GN of 130 to 150. This allows nearly instant recovery, and the use of light modifiers such as a softbox or bounce card to make the flash a little less harsh (albeit with a little reduced distance when using them).

Battery type used in a flash also makes a difference. NiCad and NiMH allow the fastest recovery time because they can put out more current (at the same voltage) for short periods of time when the flash recharges. NiMH are an improvement over NiCad's for several reasons, including greater storage capacity for more flashes before having to put in a freshly recharged set. Either are much better at this than alkaline cells, which start to drag out flash recovery time when they are about half discharged.

The only thing faster is a flash unit that allows an external high voltage battery pack (worn on the belt) that directly recharges the high voltage section of the flash. It has a cable that plugs into a special HV socket on the flash to do this. Not every flash has this capability.

Typical recovery time using a 130-150 GN flash with rechargeable NiMH cells and ISO 160 film is no more than about 1.5 seconds, usually much less.

Good luck with your beginner's course.

-- John


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6/15/2002 10:44:06 PM

 
Ken Pang   Hi Howard,

Basically what John said, except that I expand on the batteries bit.

Batteries have different characteristics which make up their qualities:

1) Potential difference, also known as the voltage. All batteries of the same size, regardless of their internal chemicals, have the same voltage. For example, all AA batteries put out 1.5 volts.

2) Current, is the unpublished and hardly known companion to the voltage, and this is where battery quality comes into it. It's hard to explain in non-technical terms, and I have no idea your training in electronics, but I'll try with an analogy. Sorry if this sounds patronising.

If I had a hose, there are two ways I can make water come out faster. I can turn the tap on faster (increase in voltage), or I can make the hose wider(increase in currents/amps).

Now, given that the voltage is fixed at 1.5volts (or whatever the CR2 battery is fixed at), you can charge your flash faster, by providing a battery that can pump out more amps at the same voltage.

In non rechargables, this is my understanding of progression of power delivery:

Carbon
Alkaline
Lithium
Titanium

Check what your CR2 battery is made of. I'd say it's most likely alkaline.

I also understand that as John said, rechargable batteries are capable of dealing out massive amps for a very short time. This is shown by the fact that if you short circuit any non-rechargable, nothing happens. If you short a rechargable, the wires get hot, usually burn your finger, ouch I just dropped it hot.

I'm actually wondering now if rechargables might be a way of getting a faster recycle time. Must try it some time.

3) The last characteristic is durability Not a real concern for recycle time, but some batteries can put out a larger watthour time. Just means more flashes per set of batteries.


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6/16/2002 6:03:08 AM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Yes . . . shorting out a rechargeable (or any battery) to test this is not recommended though . . . they can "explode" making quite a mess of your desk.

A battery has "internal resistance" which becomes part of the electrical circuit. This is what limits the amount of current a battery can put out before its voltage starts to plummet. The internal resistance of a healthy NiCad is low. It's even lower for a healthy NiMH, and it has overtaken the NiCad with capacity (how long it will last before being discharged). In addition, both are designed to withstand high output for short periods.

The internal resistance of an alkaline starts to increase at about half life, and its voltage gradually starts to decrease. By comparison both NiCad and NiMH hold their voltage very constant until the bitter end, although it's slightly lower than a new alkaline. When the NiMH cells in my flash reach near total discharge it's pretty dramatic and there's not much warning; about two or three flash cycles. Behavior (flash recovery time) until that point is very constant, and fast.

Footnote:
Rechargeable NiCad and NiMH cells also have a shelf life in holding a charge. They will self-discharge faster. This is their "downside" when used in devices that are used only occasionally. OTOH, non-rechargeable alkalines have a very, very long shelf-life.

-- John


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6/16/2002 11:04:16 AM

 
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