Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-13-2010, 02:47 AM   #1
Loyal Site Supporter
charliezap's Avatar

Join Date: Feb 2009
Location: saugus ma
Photos: Gallery | Albums
Posts: 8,213
K20d flash duration


Just a quick question--Does anyone know for sure what the flash duration is for the k20d pop up flash?This shot was taken with the Vivitar 285 HV with the yellow setting 1/30,000 sec. A similiar shot was taken with the onboard k20d flash and the stopping action was pretty darn close.---charliezap

05-13-2010, 04:07 AM   #2
Veteran Member
blende8's Avatar

Join Date: Feb 2007
Location: Bremen, Germany
Photos: Albums
Posts: 1,484
There is not the flash duration for a flash.
The duration depends on the power it is emitting.
E.g. the AF540 needs 1/200 s to give its full power, but has the shortest possible time as 1/20.000 s.
05-13-2010, 07:14 AM   #3
Site Supporter
enoeske's Avatar

Join Date: Jul 2009
Location: Surprise, Az
Photos: Gallery
Posts: 1,918
QuoteOriginally posted by blende8 Quote
There is not the flash duration for a flash.
The duration depends on the power it is emitting.
E.g. the AF540 needs 1/200 s to give its full power, but has the shortest possible time as 1/20.000 s.
The power controls the length of the flash. The longer the flash, the brighter it appears. Low power (1/64 - 1/32 power and such) are very very short durations of the flash while high power (1/2 - 1/1 power) are longer. But the flash itself is not different.

So you can measure the flash duration if you can get a consistent power setting. This likely means using a manual lens to avoid ttl. Then you will have full power flashes which will mean a long duration. I don't know of a way to set the onboard flash to low consistent power.
05-13-2010, 08:15 AM   #4
Veteran Member
blende8's Avatar

Join Date: Feb 2007
Location: Bremen, Germany
Photos: Albums
Posts: 1,484
QuoteOriginally posted by enoeske Quote
So you can measure the flash duration if you can get a consistent power setting.
Of course, yes.
IIRC the built-in flash gives full power with M-lenses always.

05-13-2010, 12:12 PM   #5
Loyal Site Supporter
charliezap's Avatar

Join Date: Feb 2009
Location: saugus ma
Photos: Gallery | Albums
Posts: 8,213
Original Poster
My question still is "how fast is the flash" in parts of a second. 1/???
05-13-2010, 12:36 PM   #6
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,397
QuoteOriginally posted by blende8 Quote
There is not the flash duration for a flash.
The duration depends on the power it is emitting.
E.g. the AF540 needs 1/200 s to give its full power, but has the shortest possible time as 1/20.000 s.
no, in fact it needs a lot less than 1/200th

the 1/180 flash sync (5.4 mS) is the whole exposure time. this time is split into 3 segments. Leading curtain opening time, full open time, and trailing curtain closing time.

generally the two curtains move at the same speed, and each could move as slow as 1/180 of a second with the trailing curtain beginning to close the instant that the leading curtain gets fully open. therefore no part of the frame is exposed for more than 1/180 of a second.,

in reality the curtain opening and closing times will be shorter than 1/180, because they do need to leave time for the flash to fire in between.

I would suspect that they actually leave about 1-2 mS of full frame open time, and full power of the flash will be tuned to that time.

I tried to get this data once from pentax but they wouldn't give it.

The best way woud be to measure a very fast spinning object of known speed, and triggering the flash at each power, 1/64th etc and measure the angular rotation of the object to calibrate the flash. Full power is a little dangerous because duration may also depend on the state of charge of the capacitor and therefore be a little inconsistent.

some flashes have minimum power settings in the 1/20,000 to 1/50,000 range, but note that flash duration doubles for each doubling of power
05-13-2010, 12:47 PM   #7
Loyal Site Supporter
charliezap's Avatar

Join Date: Feb 2009
Location: saugus ma
Photos: Gallery | Albums
Posts: 8,213
Original Poster
As a guess I would say that the K20's flash duration is around 1/10,000 sec.I will take a shot later of the h'bird with the onboard flash and try to compare it to the above photo taken at 1/30,000sec--charliezap
05-13-2010, 01:22 PM   #8
Veteran Member
blende8's Avatar

Join Date: Feb 2007
Location: Bremen, Germany
Photos: Albums
Posts: 1,484
I took the 1/200 s from the manual of the AF540.

05-13-2010, 02:11 PM   #9
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,397
QuoteOriginally posted by blende8 Quote
I took the 1/200 s from the manual of the AF540.
perhaps, but from the example I gave, you can see it must be faster than that.
05-13-2010, 05:32 PM   #10
Veteran Member
alohadave's Avatar

Join Date: Jan 2008
Location: Quincy, MA
Photos: Gallery | Albums
Posts: 2,024
QuoteOriginally posted by Lowell Goudge Quote
The best way woud be to measure a very fast spinning object of known speed, and triggering the flash at each power, 1/64th etc and measure the angular rotation of the object to calibrate the flash. Full power is a little dangerous because duration may also depend on the state of charge of the capacitor and therefore be a little inconsistent.
The very best way would be to use a thyristor or phototransister as a sensor in front of the flash connected to an oscilloscope. Alternatively, you could connect the o-scope lead directly to the contact of the flash tube.
05-13-2010, 05:49 PM   #11
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,397
QuoteOriginally posted by alohadave Quote
The very best way would be to use a thyristor or phototransister as a sensor in front of the flash connected to an oscilloscope. Alternatively, you could connect the o-scope lead directly to the contact of the flash tube.
when I get time and a storage scope
05-13-2010, 09:57 PM   #12
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by charliezap Quote
My question still is "how fast is the flash" in parts of a second. 1/???
Yes, but the answer they gave you is correct: it depends. On a shot in which the flash happened to fire at full power, it's 1/200" or whatever; but if the ISO, aperture, and subject distance are such that the flash does *not* need to fire at full power (read: most of the time) then the flash fires for less time.
05-13-2010, 10:06 PM   #13
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
QuoteOriginally posted by charliezap Quote
My question still is "how fast is the flash" in parts of a second. 1/???
From the user manual, maximum flash duration is 1/1000 sec. This is when the flash has to release its full power. If you set it to 1/16 power, the flash duration therefore will be 1/16000 sec (see partial quote from Lowell below). In automode, the flash duration can go down to 1/30000 sec (spec in user manual); there is however no way to determine what the flash duration was at the time that the photo was taken.

You might be able to do an estimation (probably more of a guess instead of an estimation) based on the physics of the bird by calculating the speed of the wings of the bird. But I leave that to to you.


QuoteOriginally posted by Lowell Goudge Quote
some flashes have minimum power settings in the 1/20,000 to 1/50,000 range, but note that flash duration doubles for each doubling of power
05-14-2010, 12:28 AM   #14
Veteran Member
blende8's Avatar

Join Date: Feb 2007
Location: Bremen, Germany
Photos: Albums
Posts: 1,484
QuoteOriginally posted by Lowell Goudge Quote
perhaps, but from the example I gave, you can see it must be faster than that.
Flash synchronization speed is the shortest time at which the curtains are fully open. This is 1/180 s for Pentax cameras.
1/200 s shortest flash duration (w. max. power) fits good here.
05-14-2010, 10:10 AM   #15
Veteran Member




Join Date: Jun 2008
Location: NJ
Posts: 1,738
Thanks for the info. I understand a little bit more the functioning of the flash.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, dslr, duration, flash, k20d, photography, shot
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
high iso in-camera processing duration k7 vs k20d navicore Pentax DSLR Discussion 4 12-09-2009 12:03 PM
Fastest flash duration + flash power reknelb Flashes, Lighting, and Studio 7 10-14-2009 08:05 PM
* Best Flash for K20D? * PentaxForums-User Flashes, Lighting, and Studio 6 07-14-2009 04:15 PM
flash duration Lowell Goudge Flashes, Lighting, and Studio 2 07-03-2009 03:29 PM
Help with old flash on K20D winglik Pentax DSLR Discussion 5 02-28-2009 06:02 AM



All times are GMT -7. The time now is 02:02 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top