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09-13-2012, 04:03 PM - 5 Likes   #1
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Flash Duration Measurements - AF-540FGZ

If you search the web for information on the flash duration of the Pentax top-of-the-line flash, the AF-540FGZ, you find precious little real information, other than a few values accredited to Pentax (for which I can not actually find anything from Pentax - anybody know where to find it?).

I have remedied this! I have made direct measurements of the '540 flash output light curve for all power levels, from full to 1/64 power. I then determined the t-0.1 and t-0.5 durations. I also determined what I call the P50 and P90 values - the durations over which 50% and 90% of the total light output is emitted during a flash event. I think these "P" parameters are more meaningful than the "t" values if you are trying to use the flash for stop-action photography, as I want to do (water drop pictures).

Go to photodave.us/AF540FGZ to see my data and results. I used a fast phototransistor and a digital storage oscilloscope to record the light curves. You can see 'scope screen image dumps that show the light curves.

Comments welcome.

09-13-2012, 06:31 PM   #2
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QuoteOriginally posted by AstroDave Quote
If you search the web for information on the flash duration of the Pentax top-of-the-line flash, the AF-540FGZ, you find precious little real information, other than a few values accredited to Pentax (for which I can not actually find anything from Pentax - anybody know where to find it?).

I have remedied this! I have made direct measurements of the '540 flash output light curve for all power levels, from full to 1/64 power. I then determined the t-0.1 and t-0.5 durations. I also determined what I call the P50 and P90 values - the durations over which 50% and 90% of the total light output is emitted during a flash event. I think these "P" parameters are more meaningful than the "t" values if you are trying to use the flash for stop-action photography, as I want to do (water drop pictures).

Go to photodave.us/AF540FGZ to see my data and results. I used a fast phototransistor and a digital storage oscilloscope to record the light curves. You can see 'scope screen image dumps that show the light curves.

Comments welcome.
This is really good work... You don't happen to the a Metz AF58 Kicking about? I would love to see comparible results.
@Adam The forum Admin might wish to add this to any AF 540FGZ In-Depth- Reviews that might be coming up in the future. You seem to have been very meticulous in your testing methods for which I applaud you!
09-14-2012, 06:31 PM   #3
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Sorry, no Metz's lying around. Send me one, and I can make some measurements!
09-20-2012, 01:36 PM   #4
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QuoteOriginally posted by AstroDave Quote
If you search the web for information on the flash duration of the Pentax top-of-the-line flash, the AF-540FGZ, you find precious little real information, other than a few values accredited to Pentax (for which I can not actually find anything from Pentax - anybody know where to find it?).

I have remedied this! I have made direct measurements of the '540 flash output light curve for all power levels, from full to 1/64 power. I then determined the t-0.1 and t-0.5 durations. I also determined what I call the P50 and P90 values - the durations over which 50% and 90% of the total light output is emitted during a flash event. I think these "P" parameters are more meaningful than the "t" values if you are trying to use the flash for stop-action photography, as I want to do (water drop pictures).

Go to photodave.us/AF540FGZ to see my data and results. I used a fast phototransistor and a digital storage oscilloscope to record the light curves. You can see 'scope screen image dumps that show the light curves.

Comments welcome.
Outstanding work, thank you.

If I had "give a gold shiney" powers as a moderator I would =)

09-20-2012, 08:18 PM   #5
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Wow - FORTRAN! I haven't seen FORTRAN code since 1986.

Very Nice work.

So, correct me if I'm wrong here please, it is safe to think of the 540 as a 1/200s flash. Meaning in the worst case scenario (full power) it is capable of freezing motion as effectively as a 1/200s exposure in ambient light. And by 1/16th ~ 1/32nd power you have exceeded the effective shutter speed of any Pentax camera. Is that generally accurate?
09-23-2012, 09:44 PM   #6
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Fortran - the only way to go!! I've been using it since 1963! I've never found anything I can't do with it - although it may get a little convoluted sometimes.

Your synopsis of flash speeds compared to shutter speeds seems about right to me, as an alternate way of thinking about it. The '540 at full power is certainly no speed demon, and the t-0.1 time is right at 1/200 second. Because the light peaks rapidly and then falls off more leisurely, depending on the situation (i.e. the flash supplying most, but perhaps not all the light) you might think of it as being a little faster, but not by a lot. You can take interesting pictures with the flash of things that are moving several times their size in that 0.005 second: you'll see the "head" of the motion being brightest, with the object streaking past and fading away (I did this with the water drops from my bathroom shower head).
09-23-2012, 09:58 PM   #7
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Why would anyone purposefully subject themselves to Fortran? :P

"Friends don't let friends code Fortran"

That said, I still use it at work since a lot of legacy modules and systems use it...

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