[dmfw]

I am using a Pentax KX, and I wanted to know how I can tell if it safe to use an older flash with my camera's hot-shoe. I know that there is a voltage issue with older flashes, but without the specs how can one tell?

The two flashes are about 15 years old and I know that there was used on a film camera. The units are a Vivitar 125 and a Sunpack Auto 411. The both function and are being used as remote flashes.

[Pioneer]

RiceHigh's Pentax Blog: Which Flash Units are Safe for Pentax DSLRs?

Go to this site and read all about it.

[jatrax]

You can check here: Photo Strobe Trigger Voltages Pentax has not said exactly what is safe but most consider 12volt fine and 24volt probably OK, anything higher I would not use.

Just FYI the KX is an older film camera, the k-x is digital. I assume you mean the digital, but if not then please disregard.

[stevebrot]

You can check here: Photo Strobe Trigger Voltages Pentax has not said exactly what is safe but most consider 12volt fine and 24volt probably OK, anything higher I would not use.

If your flash is not listed, you can measure the voltage directly using a voltmeter across the center contact and side contacts of the flash shoe.


Steve

[lmd91343]

If your flash is not listed, you can measure the voltage directly using a voltmeter across the center contact and side contacts of the flash shoe.


Steve

Will a DVM respond fast enough? If it does respond fast enough will the value stay displayed long enough to read?

I use this:

Wein SSHSHS Safe-Sync Hot Shoe to Hot Shoe, PC Socket 990560

There is also a slightly cheaper one that will only work with PC cords. The sample will work with shoes and cords.

[elliott]

Will a DVM respond fast enough? If it does respond fast enough will the value stay displayed long enough to read?

The voltage at charging and charged are what you're measuring. There is always a voltage on the hotshoe contacts, not just when the flash fires.

I was curious to see if there is a spike when firing and checked with my oscilloscope, the most I saw on a safe flash was maybe another 2V for a very, very short period of time. I tested 3 different Vivitar 285HVs, Chinese, Korean and Japanese made.

[Tako Kichi]

Will a DVM respond fast enough? If it does respond fast enough will the value stay displayed long enough to read?

You are measuring the voltage across the shoe terminals and not the voltage across the xenon tube at the instant of the flash so a DVM will read the voltage just like reading the voltage across a battery.

Depending on the circuitry involved the voltage could be the voltage of the battery pack (or slightly less) or many times higher if the shoe contacts form part of the high voltage tube circuit.

[lmd91343]

You are measuring the voltage across the shoe terminals and not the voltage across the xenon tube at the instant of the flash so a DVM will read the voltage just like reading the voltage across a battery.

Depending on the circuitry involved the voltage could be the voltage of the battery pack (or slightly less) or many times higher if the shoe contacts form part of the high voltage tube circuit.

The point I am making is that cheap DVMs and multimeters are incapable of reading the short spike and displaying it long enough to have it read. One ten thousandth of a second is just too short a time for most meters. The meter will not display the right value at human reading speed. You then would be using false data to make a decision. Then you might burn up your camera with a flash whose voltage was improper.

Don't do it! Use a wein safety device between the flash and camera.

[AquaDome]

If you have a good digital multimeter, it will have Fast-Sampling, plus Peak and Hold settings, which will display the peak voltage and hold it on the display. (Fluke 287 & 289)
An oscilloscope is the way to do it. The entire amplitude will be displayed real time and can be held on the screen if set to sync.
A flash can't outrun a bottom-of-the-line 20MHz scope.

[lmd91343]

Let's stay on topic.

The OP wants to know how to find if an older flash is safe.
OP probably does not have a Fluke meter that costs $480 - $580 or an O-scope. OP probably has an inappropriate cheap DMM or none. If OP had the right meter, they would not be asking.

The simple response for the OP is you can't use a cheap meter. If you want to use the unknown old flash buy the wein device.

[elliott]

The OP wants to know how to find if an older flash is safe.
OP probably does not have a Fluke meter that costs $480 - $580 or an O-scope. OP probably has an inappropriate cheap DMM or none.

There isn't any appreciable spike on any flash I've tested when it is fired. The voltage you're measuring is not a quick pulse, it is relatively constant. I saw a little bit of a voltage rise for a few microseconds, but that could be just from discharging a high voltage xenon tube near the probe. I don't remember the numbers exactly, it has been a few years, but I remember that it was barely worth mentioning.

[lmd91343]

Elliot,

I've not measured any flash in years. I am not going to measure a flash. I don't need to.

I am telling the OP not to use an old, unknown flash. They probably do not have the proper equipment to do the checking or they would not be asking.

You have provided good info about the Vivitar 285HV strobes. That is helpful.

[AquaDome]

Let's stay on topic.

The OP wants to know how to find if an older flash is safe.
OP probably does not have a Fluke meter that costs $480 - $580 or an O-scope. OP probably has an inappropriate cheap DMM or none. If OP had the right meter, they would not be asking.

The simple response for the OP is you can't use a cheap meter. If you want to use the unknown old flash buy the wein device.

I answered HOW. You answered DON'T. Both answers are appropriate.
The Wein Safe-Sync is about twice the price of a used 20MHz oscilloscope and only does one thing, if it turns out you need it.

[elliott]

The Wein Safe-Sync is about twice the price of a used 20MHz oscilloscope and only does one thing, if it turns out you need it.

You're not going to catch a spike when firing with an analog scope unless you are a masochist with one of the Polaroid attachments. You need a digital scope to do single shot capture easily.

[Tako Kichi]

Just out of idle curiosity I decided to dig into the back of the closet and drag out my box of old film camera gear to test my two old and ancient flash units. I used a brand new set of alkaline AA cells and my 15+ years old DVM.

These were the flash units I tested (not my photos but found online):



A Fotomatic 700 TFZ

and



A Nissin 400HA

This is an almost identical DVM to the one I used apart from the brand name (mine is branded as a 'Smart2' which was an old Radio Shack 'store' brand).



I inserted the batteries, set the DVM to the '300' range (upper dial) and 'DC V' option (lower dial) and tested the voltage between the centre 'hot-shoe' contact (+ve lead) and the 'side rail' contact (-ve lead) once the flash units had charged up. In both cases the voltage initially read around 245 V DC and then slowly started to climb at roughly 0.1 volts per second until I stopped taking readings when both units had exceeded 250 V DC.

Needless to say I will not be using either of these units on my K30 but they could still be used as slave units if hooked to my 30 year old 'magic eye' trigger or some other more modern slave trigger system.

To reinforce what I said in an earlier post you are not trying to capture the voltage at the instant the xenon tube fires but measuring the voltage the flash unit puts across the 'hot-shoe' contacts when it is in it's charged state. 250 V DC is way too high a voltage for most DSLR cameras to tolerate and the reading I've done recently seems to indicate that most DSLR cameras fall into the 6-20 V DC range in terms of 'safe voltage' depending on the make/model of the camera.

The bottom line is test your gear and do your research before you put the flash on the camera.