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05-20-2015, 10:17 AM   #1
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Older flash - safe for my K5??

I am aware that older and/or not-completely-compatible third-party flashes have the theoretical ability to send power pulses into a DSLR that can scramble the electronics and produce expensive paperweights. But what of older brand-name equipment?

I have in my hot little hands a Pentax AF200SA flash, which appears to originally have been bought for a Pentax P3. It's brutally basic, with a head that neither tilts nor swivels, and it demands four AA batteries. On the back is a single on-off switch and a ready/test switch. There is a statement describing the control range as 0.8 to 5 metres (presumably as master) with equivalent feet measurement, and a red sticker with "For Pentax Program" on it, plus "Asahi Opt. Co. Japan". That ought to date it for the experts!!

On the shoe (which secures with a knurled wheel), there are three contact points arranged in a roughly equilateral triangle - one central and two towards the rear, abreast each other.

Do I dare to mount this flash on my K5? And what should I expect if I do?

05-20-2015, 10:42 AM   #2
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the trigger voltage is 6.2V, So there is no problem there. if you do not have the manual, here's a link to it,

http://c2b6d376b97bcc466063-5420c200a1f030d1394a9548df6eadbd.r5.cf2.rackcdn.com/files/support/manual/97_1314744913-616018176_manual.pdf

Not a very powerful flash, guide number 20 at 100 ISO, but it could be useful.
05-20-2015, 10:44 AM   #3
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It really has nothing to do with whether it is 'name brand' or not. Back in film days much higher voltages were used.

Here is the most extensive list I have found: Photo Strobe Trigger Voltages You can also test the voltage yourself if you have a multi-meter. I believe Pentax has hinted that 20 volts or less is OK. I suggest not using anything over 12 volts to be on the safe side.

I have 3 AF200T Pentax flashes and have used them for years with no issues if that helps.
05-20-2015, 11:23 AM   #4
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Thanks all. I think I've got a multimeter somewhere at home, along with a whole lot of batteries. Which contacts do I touch between? Or should I just try them all and look for the highest result?

05-20-2015, 12:05 PM   #5
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This is a so-called auto-thyristor flash; this type of flash determines correct exposure by itself. This specific model is very limited in that it is designed for one iso and one aperture (if you increase iso on the camera, you also have to increase the aperture number of the lens).

But you can play a bit. Using a narrower aperture (e.g. f/5.6 on the camera instead of the f/4 in the table in the manual) will basically result in a negative flash exposure compensation (of one stop for the example); in the same way you can create a positive flash exposure compensation by choosing a wider aperture. If you don't want to change the aperture, you can achieve the same by changing the iso (limitation is that the K5 can't do iso 50).

Stay away from auto-iso and have fun.

---------- Post added 20-05-15 at 21:07 ----------

QuoteOriginally posted by pathdoc Quote
Thanks all. I think I've got a multimeter somewhere at home, along with a whole lot of batteries. Which contacts do I touch between? Or should I just try them all and look for the highest result?
The part that will touch the metal outside of the camrra hotshoe and the center pin.
05-20-2015, 03:59 PM   #6
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If in doubt about the trigger voltage of that flash, or any other old flash, it may be worth getting a Cactus v6 wireless flash trigger.

It costs extra, but aside from being useful for remote flash, the v6 also has the feature of being a 'safe-sync', allowing you to mount flashes on it with a trigger voltage of up to 300V, and then safely use them on camera. It's handy to have around.

Last edited by rawr; 05-20-2015 at 04:04 PM.
05-22-2015, 07:01 AM   #7
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Someone who knows what they are doing (because they do it for a living) and who also knows cameras has measured it for me at 7.58 volts, so I should be good to go.
05-22-2015, 07:09 AM   #8
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QuoteOriginally posted by pathdoc Quote
Thanks all. I think I've got a multimeter somewhere at home, along with a whole lot of batteries. Which contacts do I touch between? Or should I just try them all and look for the highest result?
trigger voltage is between center pin and the shoe contact (side rails)

be careful wit multi meters, many low cost ones have variable input impedance as a function of range, and can load the trigger and give false, (low) readings

05-22-2015, 07:20 AM   #9
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QuoteOriginally posted by sterretje Quote
limitation is that the K5 can't do iso 50
I have tried all the combinations from ISO 100 to 1600 in the table provided with the instruction manual linked above, and I can't tell the difference in exposure looking at them in-camera (I photographed my bookshelf from across my darkened office). I also went beyond, to ISO 3200 and f22, and things looked okay there too. Results for f/2.8 and ISO 80 were near enough to everything else that I don't feel uncomfortable using that in future (naturally more trials will be needed).

The next thing is to see what happens when the flash is nominally out of range and compensatory amounts of aperture are dialled in. I don't expect stellar results here, but it should be fun!

---------- Post added 05-22-15 at 11:53 AM ----------

QuoteOriginally posted by Lowell Goudge Quote
trigger voltage is between center pin and the shoe contact (side rails)

be careful wit multi meters, many low cost ones have variable input impedance as a function of range, and can load the trigger and give false, (low) readings
The measuring was done by a professional who works in hospital biomedical engineering, so I think I can trust the competence of both the device and the person using it. I also showed him the instructions from the article quoted above before we started, so we've got it as right as we possibly can.
05-22-2015, 07:26 AM   #10
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QuoteOriginally posted by pathdoc Quote
snip.....
The measuring was done by a professional who works in hospital biomedical engineering, so I think I can trust the competence of both the device and the person using it. I also showed him the instructions from the article quoted above before we started, so we've got it as right as we possibly can.
No offence to the person who makes the measurement, it is just some times people forget that instruments are not all created equal.
05-22-2015, 07:44 AM - 1 Like   #11
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QuoteOriginally posted by Lowell Goudge Quote
it is just some times people forget that instruments are not all created equal.
True. That's one reason WHY I had it done the way I did - my multimeter is an electronics-shop cheapo, and I didn't want to put my camera at risk by doing it wrong with shoddy instruments. The multimeter that was used is also used to repair machinery that keeps very sick people alive, so I could trust them to have the best.
05-22-2015, 08:26 AM   #12
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QuoteOriginally posted by pathdoc Quote
I have tried all the combinations from ISO 100 to 1600 in the table provided with the instruction manual linked above, and I can't tell the difference in exposure looking at them in-camera (I photographed my bookshelf from across my darkened office)
They should not differ.

QuoteOriginally posted by pathdoc Quote
The next thing is to see what happens when the flash is nominally out of range and compensatory amounts of aperture are dialled in. I don't expect stellar results here, but it should be fun!
I did think about this for my previous reply. What will happen is that the flash will blast full power because it (thinks it) can't expose properly. So it essentially becomes a manual flash with only full power and you have to adjust ISO and aperture on the camera / lens to get the correct exposure.
05-22-2015, 09:44 AM   #13
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QuoteOriginally posted by Lowell Goudge Quote
No offence to the person who makes the measurement, it is just some times people forget that instruments are not all created equal.
QuoteOriginally posted by pathdoc Quote
True. That's one reason WHY I had it done the way I did - my multimeter is an electronics-shop cheapo, and I didn't want to put my camera at risk by doing it wrong with shoddy instruments. The multimeter that was used is also used to repair machinery that keeps very sick people alive, so I could trust them to have the best.
Be careful with assumptions. You have people using instruments explicitly specified for a piece of equipment to produce a repeatable and certifiable result, this does not imply explicitly "the best" . I am pretty sure it was adequate for the task at hand, but I am always reminded by a quote, I forget now who it is attributed to "Assumption is the mother of all screw-ups"
05-22-2015, 10:26 AM - 1 Like   #14
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Let me rephrase that more explicity - the best available to me with a reasonable amount of effort in a reasonable time frame.
05-22-2015, 12:29 PM   #15
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Update:

I've tried this thing out with two lenses now: an M42 135mm f/2.8 and then the DA 50mm f/1.8.

In the former case (described above), using the published tables yielded quite acceptable results. The camera detected that there was a flash and set a sync speed of 1/180 s.

In the latter, things got more interesting because the camera knew which lens was grafted to it. It chose a sync speed of 1/90 of a second. In AP mode, the results were as described above. Excellent results were achieved out of nominal maximum range by opening the lens right up. In program mode, altering the ISO produced aperture settings according to the table in the instruction manual and this stayed true all the way up to ISO3200, at which point I was up at f/22 anyway and it couldn't close down any further.

I will have to try it with the 28mm M mount lens and see what it does with that.

UPDATE: Again, the camera sensibly detects that there is a flash (albeit an older one) fitted. In M mode, with the Vivitar 28/2.8 applied and the tape trick used to let it stop down, the camera applies a ceiling shutter speed of 1/180 and from that point all is pretty much routine. Ironically the old M42 with its stop-down metering is the friendlier of the two to use as it can be shot in Aperture Priority mode and all you have to worry about is the focusing and selection of aperture according to desired ISO!!

Last edited by pathdoc; 05-22-2015 at 04:06 PM. Reason: further information
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