Which Flash Units are Safe for Pentax DSLRs?

Do you have an old flash unit that you want to use on your Pentax DSLR? Do you need to buy a new flash gun for your Pentax DSLR for whatever reason but wish to consider an alternative other than Pentax dedicated ones (now only the AF360FGZ and AF540FGZ which exclusively support the Pentax K series DSLRs)?

Actually, the two main concerns by the users are:-
1. Will they work? (and how good do they work?)
2. Are they safe to use? Will the flash units damage the camera body?

For the first question, my answer is that *normally* they will work, i.e., the DSLR body can control the flash gun to fire, when the shutter is opened. On the other hand, for how good those flash units will work, it actually mostly depends on the quality of the flash units and how good they are designed and built for the performance aspects, e.g., exposure accuracy.

For the second question, before going further, I think everyone should read this page to begin with:-

http://www.botzilla.com/photo/strobeVolts.html

So, for the "flash trigger voltage" mentioned, it is simply the voltage that appears across the electrical pins of the "positive" and the "ground" of the flash unit's foot *when* the circuit is opened (at the hotshoe), before the flash unit discharges (when at the hotshoe the circuit is closed, i.e., switching on).

So, how to measure this "trigger voltage"?

Just see this for the detailed illustration:- http://www.botzilla.com/photo/g1strobe.html#danger

In short, it's very simple to measure. Just use a voltmeter to measure the voltage across the positive central pin (corresponding to the largest contact on the hotshoe) and the ground(s), i.e., the metallic contact(s) at the side(s) *inside* the foot of the flash unit's hotshoe stand.

But there are something more to note when doing the measurement, which is not mentioned in the above article, in order to obtain the most accurate results:-

1. Fresh batteries should be used, as later on you can see battery voltage could affect the trigger voltage of some flash units, quite significantly, usually for those old types;

2. Use alkaline batteries, which are of around 1.5V when new, so as to measure the possible highest trigger voltage out of the flash units;

3. Ensure hard press of voltmeter's probes to the metal pins of the flash unit so as to ensure very good electrical contact so as to avoid any possible drop in the measured voltage;

4. Be sure to turn on the flash unit during measurement;

5. Be sure to measure the trigger voltage as soon as possible when the ready lamp is lit (so as to avoid possible further self discharge which will lower the measured voltage - some designs would not continuously recharge the flash once the "ready" threshold has been reached).

For what I have measured for my Pentax AF240FT, a Canon Canolite D and a Vivitar 2800, the trigger voltages with a new set of Panasonic Alkalines are 2.7V, 185V and 180V respectively. If I replaced a set of freshly charged Sanyo 2500 mAh NiMHs, the measured voltages are then 2.7V, 165V and 160V respectively.

It is interesting to note that my year 1988 AF240FT dedicated Pentax AF TTL auto flash gun (1st generation of its kind) does have some kind of regulation of the trigger voltage which is extremely stable, regardless of the battery voltage and status. On the other hand, my 1978 bought Canolite D and the plainly old designed and inferiorly built Vivitar manual-set auto flash both do not have any kind of voltage regulation nor voltage suppression so that the trigger voltage can be very high at 180 or 185V DC!

So, let's come back to the Pentax (DSLR) case. Can all those different types of flash guns work on Pentax DSLRs? My guessed answer is Yes. They will work *as long as* *both* the camera and the flash are working together! ;-) I have had no problem in using any of the above three flash units on any of my three different models of Pentax AF film SLRs and another three different models of Digital SLRs. But anyone should be aware of the excessive trigger voltage which *might* damage the electronic controlled switching part of those newer electronics cameras (not only Pentax ones), as explained in details in the last quoted article, here.

All in all, what we *first* need to check is: 1. the trigger voltage of your flash unit(s) in doubt and; 2. the maximum voltage which the newer Pentax DSLRs can tolerate. (Note that I have highlighted the word *first* above and I shall explain more in details for what does this mean :-))

For the various different trigger voltage values measured by various different users of the net community, we can browse through "the strobe list" summary table in the following page:-

http://www.botzilla.com/photo/strobeVolts.html

As for the maximum toleratable "safe" voltage of the Pentax DSLR bodies, *for long term usage*, it remains a mystery. But it can be seen in the following discussion page for some of the reported cases, in which some reference information can be found:-

http://www.botzilla.com/photo/photoBook/pbook.html#msg200

"Pentax (germany) informed, that the maximum-voltage for DSLR's *istD + *istDS is 30 Volt
Positive in the middle."

"I checked a new Vivitar 285HV with Quest rechargable batteries and got 13.31 volts. I have burnt the sync out of two Pentax AF bodies in the last year."

So, if the first claim is true, then the Pentax DSLRs are actually ISO 10330 compliance. However, since there is also user report of burnt camera for using a flash unit of trigger voltage at such a lower voltage of 13.31V, I think we should be more susceptible to the potential hazard here. As long as the trigger voltage is concerned, I think it would be safe enough to check the maximum trigger voltage amongst all the original Pentax units in the trigger voltage summary table, as the bottom line. It can be seen that the highest voltage reported is 7.8V, for the AF200/280T.

So, as all Pentax original flash guns should be safe to be used on any Pentax SLRs, can we assume that if we have a flash unit which has a trigger voltage lower than 7.8V, then it will be safe for use on our Pentax DSLRs? I am afraid that the answer is simply No, in contrary to what the author of the above "trigger voltage" page suggests!

Why? Still remember the thyristor capacitor for the switching job for modern SLR bodies? Actually a thyristor is an electronic device. Any electronic device has a maximum tolerance on the voltage, but also the *current* and thus a theoretical maximum power that could apply to it before it could be permanently damaged or when it refuses to work temporarily. The same even applies to mechanical electrical switches, although the maximum ratings can be (much) higher.

It is therefore checking the voltage is the first thing to do and actually it is the easiest and simplest to check. However, if the current is over, that could still damage the thyristor component if it is out of the maximum toleratable value. So, afterall, I would recommend it is stll the safest to use only original Pentax flash guns on Pentax DSLRs, even though we have only two choices (of two models) up till now (and very soon there will be three - but with a new useless model added, which is underpowered and rather crude to be useful) and despite that all the older Pentax TTL dedicated auto flash will have no auto control function on *any* of the Pentax K series DSLRs.

Nonetheless, if you still wish to take the risk by using any non-Pentax flash unit on your Pentax DSLR, do at least try to measure the trigger voltage and see if it is not more than 7.8V. Do note again that the author of my quoted page does warn about the potential damage to our cameras for long term use of a high trigger voltage flash unit on them, anyway.