Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-19-2013, 08:08 AM   #46
Pentaxian




Join Date: Sep 2012
Photos: Gallery | Albums
Posts: 1,728
If you know the minimum possible distance between leading and trailing shutter curtains, you can get some idea of what the theoretical maximum sync speed can be. The K-5 can do 1/8000 sec exposure and I presume the curtains move at a uniform speed regardless of set shutter speed... it's only the timing (and therefore distance) between the two that changes. Is that correct? If so and if the physical limitation on sync speed really is 1/180 sec. then you can surmise that the minimum distance is only 2.25% of the sensor height (180 / 8000 = 0.025). That's a darn small traveling slit, IMHO, so it seems that the 1/180 is not the physical limitation but rather a software limitation.

06-19-2013, 08:42 AM   #47
Site Supporter
JimJohnson's Avatar

Join Date: Jan 2012
Location: Lake Superior - Michigan
Photos: Gallery
Posts: 2,271
QuoteOriginally posted by thechumpen Quote
That's what I was thinking as well. Although pretty sure you need an external flash for that. At least my K-r does - there is no HSS option when using the inbuilt flash. However, if I use my Metz flash and set it to PTTL-HSS then I can get much faster shutter speeds (can't recall exact upper limit).
HSS is a contrived fiction.

Your shutter is made up of two curtains, leading and trailing. The leading curtain ALWAYS takes 1/180 seconds to completely open and the trailing curtain ALWAYS takes 1/180 seconds to close the shutter. Exposure time is determined by a slit of light moving across the sensor.

Using a shutter speed of 1/180 seconds, the entire exposure gate is open. Since this is the fastest shutter speed in which the entire gate is open, this is called X-Sync. (Side note: X is for electronic flash. Older cameras also supported M-Sync which is for flash bulbs.) Since both curtains travel the gate at 1/180 second, the trailing curtain starts its trip as soon as the leading curtain has made its crossing.

For shutter speeds slower than 1/180 seconds, the trailing curtain waits a certain amount of time after the leading curtain has made its 1/180 trip, before the trailing curtain makes its 1/180 trip. This creates a wider slit of light moving across the sensor, and therefore a longer exposure.

For shutter speeds faster than 1/180 seconds, the trailing curtain starts its 1/180 trip before the leading curtain finishes its 1/180 trip. This creates a narrower slit of light moving across the sensor, and therefore a shorter exposure.

If an electronic flash fires only once at a shutter speed higher than 1/180 seconds, you would only have a slit of light across the frame equal to the flash duration. As noted, Pentax prevents this from happening by disabling the flash at speeds higher than X-Sync.

For High Speed Sync (HSS) flash, the flash has to fire multiple times in rapid succession for 1/180 seconds to uniformly light the subject while the narrow slit moves across the sensor. This takes a considerable amount of power and I am guessing that Pentax engineers decided there wasn't enough room inside the camera body for the large capacitors needed to store this much power. If I am correct, this is why HSS can be triggered by the built-in flash for wireless control of a HSS flash, or the HSS flash can be mounted on the hotshoe, but the built-in flash itself cannot do HSS.

Because of the multiple strobe during HSS, HSS is probably not the best choice for action photography. It would be better used for still subjects to create fill in bright sunshine where a high shutter speed is desired.

Last edited by JimJohnson; 06-19-2013 at 10:33 AM.
06-19-2013, 09:20 AM   #48
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
QuoteOriginally posted by IchabodCrane Quote
I presume the curtains move at a uniform speed regardless of set shutter speed... it's only the timing (and therefore distance) between the two that changes. Is that correct? If so and if the physical limitation on sync speed really is 1/180 sec
From what I have gathered from my sources, the shutter blades are moving around 7 m/s.This holds true no matter what "shutter speed" you are using, the light that hits the sensor is merely controlled by the increasingly smaller distance between the shutter blades as the "shutter speed" goes up.

And I have empirically proved the physical flash synch speed limit exists with this image:


Last edited by Digitalis; 06-19-2013 at 09:31 AM.
06-20-2013, 11:21 AM   #49
Senior Member




Join Date: Oct 2012
Location: weston-super-mare
Posts: 231
Original Poster
QuoteOriginally posted by IchabodCrane Quote
If you know the minimum possible distance between leading and trailing shutter curtains, you can get some idea of what the theoretical maximum sync speed can be. The K-5 can do 1/8000 sec exposure and I presume the curtains move at a uniform speed regardless of set shutter speed... it's only the timing (and therefore distance) between the two that changes. Is that correct? If so and if the physical limitation on sync speed really is 1/180 sec. then you can surmise that the minimum distance is only 2.25% of the sensor height (180 / 8000 = 0.025). That's a darn small traveling slit, IMHO, so it seems that the 1/180 is not the physical limitation but rather a software limitation.
I would like to know what camera and what settings were used by Digitalis in post no. 48 as I am unable to get any of my three Pentax digital cameras to fire a flash above the 1/180 standard speed. My Cosina C1 would produce images like this at varying heights according to the speed set as the blinds move from the bottom of the camera body to the top and the image is then inverted by the lens. 0f course with the lens removed and the back open this is easy to see without going to the bother of developing film.

06-20-2013, 01:21 PM   #50
Senior Member




Join Date: Oct 2012
Location: weston-super-mare
Posts: 231
Original Poster
QuoteOriginally posted by pentasonic49 Quote
I would like to know what camera and what settings were used by Digitalis in post no. 48 as I am unable to get any of my three Pentax digital cameras to fire a flash above the 1/180 standard speed. My Cosina C1 would produce images like this at varying heights according to the speed set as the blinds move from the bottom of the camera body to the top and the image is then inverted by the lens. 0f course with the lens removed and the back open this is easy to see without going to the bother of developing film.
I have been looking up some specs which may be interesting, The MZS shutter 1/6000 sync @ 1/180 1st D 1/4000 SYNC@ 1/150 . Every Pentax D slr after the 1st D has sync of 1/180 whether they have shake reduction or not. Also reading the specs for the Metz flashguns gives the flash duration of 1/125 @1/1 power which would give a darker picture at Xsync than at slower speeds. The table of flash duration times is weird to say the least and it's not just my 48 AF-2, their top of the range has strange figures too.
06-20-2013, 01:42 PM   #51
Veteran Member
maxfield_photo's Avatar

Join Date: Mar 2011
Location: Cincinnati, OH
Posts: 1,215
QuoteOriginally posted by pentasonic49 Quote
Also reading the specs for the Metz flashguns gives the flash duration of 1/125 @1/1 power which would give a darker picture at Xsync than at slower speeds. The table of flash duration times is weird to say the least and it's not just my 48 AF-2, their top of the range has strange figures too.
It's important to note that Metz uses the t.1 figure when citing their flash durations, where as most companies use the t.5 figure to make their flashes seem quicker on paper than they actually are. T.1 times are important to know when you are trying to freeze motion, but are slightly less critical when determining the shutter's effect on flash contribution.
06-20-2013, 01:53 PM   #52
Senior Member




Join Date: Oct 2012
Location: weston-super-mare
Posts: 231
Original Poster
QuoteOriginally posted by maxfield_photo Quote
It's important to note that Metz uses the t.1 figure when citing their flash durations, where as most companies use the t.5 figure to make their flashes seem quicker on paper than they actually are. T.1 times are important to know when you are trying to freeze motion, but are slightly less critical when determining the shutter's effect on flash contribution.
I don't understand the t.1 but I thought that if 1/1 full power is 1/125, then 1/2 power would be 1/250 but it's 1/900 and 1/4 power is 1/2000 ---------- 1/128 power is 1/25000, it's not linear or logarithmic.
06-20-2013, 04:53 PM   #53
Veteran Member
Anvh's Avatar

Join Date: Sep 2011
Posts: 4,616
QuoteOriginally posted by Digitalis Quote
Because of my knowledge of the mechanics of camera shutter systems. If the the sole light source is flash, and a shutter speed higher than the recommended synch speed is used, a blade of the shutter will be covering part the sensor while the flash is fired there will be a unexposed(black)area in the frame. The amount of the frame that will be unexposed depends on how far the recommended synch speed is exceeded.

PS:

As we all know, the hot shoe on pentax DSLR cameras goes cold when shutter speeds higher than the synch speed are used(without HSS enabled flash hardware) so I got my Pentax K5IIs and linked the shutter release remotely to my Nikon D4 which was set at its synch speed of1/250th which in turn triggered my studio strobes. After several attempts, this is what I got from my Pentax K5IIs with my sigma 180mm f/3.5 APO EX and a synch speed of at 1/250th with my Elinchrom BRX 500 fired at a blank wall @ 1:1 power*
Thank you for the test, that solved that puzle.

Your knowledge of a shutter mechanics was not something i was in doubt with but you never know how perservative Pentax was with their sync speed. Wombat Olympus is a good example. So unless you know exactly how far and how fast the shutter need to travel you can not even make a guess, i doubt you know those data. Atleast when i asked last time you didn't gave them.

06-20-2013, 05:05 PM   #54
Veteran Member
Anvh's Avatar

Join Date: Sep 2011
Posts: 4,616
QuoteOriginally posted by IchabodCrane Quote
If you know the minimum possible distance between leading and trailing shutter curtains, you can get some idea of what the theoretical maximum sync speed can be. The K-5 can do 1/8000 sec exposure and I presume the curtains move at a uniform speed regardless of set shutter speed... it's only the timing (and therefore distance) between the two that changes. Is that correct? If so and if the physical limitation on sync speed really is 1/180 sec. then you can surmise that the minimum distance is only 2.25% of the sensor height (180 / 8000 = 0.025). That's a darn small traveling slit, IMHO, so it seems that the 1/180 is not the physical limitation but rather a software limitation.
Ah but you made one error.

because of the SR the sensor actually needs more room, so your shutter is bigger then the sensor. no idea how large it actually is...

So question with the photo of Digitalis, if the sensor would be moved at the top of the SR range what would then still have the shutter in the image?
You can move the sensor manually with the K5 so Digitalis ready for another round

we've the Style RX flashes but not the computer software so can;t do the test myself.
06-20-2013, 05:19 PM   #55
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
QuoteOriginally posted by pentasonic49 Quote
I don't understand the t.1 but I thought that if 1/1 full power is 1/125, then 1/2 power would be 1/250 but it's 1/900 and 1/4 power is 1/2000 ---------- 1/128 power is 1/25000, it's not linear or logarithmic.
Yes and no. At short durations the flash is roughly linear, i.e. time dependant, but the higher the power, you begin to see the exponential decay of the main capacitor as it discharges into the flash tube, so very high powers may fall outside of the linear portion.
06-20-2013, 06:18 PM   #56
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
QuoteOriginally posted by pentasonic49 Quote
I would like to know what camera and what settings were used by Digitalis in post no. 48 as I am unable to get any of my three Pentax digital cameras to fire a flash above the 1/180 standard speed.
If you read Post #39 I give a detailed account of exactly how I managed this, suffice to say using my method of syncing at faster speeds without using HSS is well beyond the means of most photographers. The equipment required to do it cost well over $10,000.

QuoteOriginally posted by Anvh Quote
So unless you know exactly how far and how fast the shutter need to travel you can not even make a guess, i doubt you know those data.Atleast when i asked last time you didn't gave them.
I did, Actually. We know is that the shutter has to be able to cover a sensor 23.7 x 15.7 mm, so we can work from that figure give a generous 3mm -/+ clearance around the sensor to allow for the SR. As for shutter velocity, with your average vertical travel focal plane shutter the velocity of the blades is approximately 7 m/s

QuoteOriginally posted by Anvh Quote
So question with the photo of Digitalis, if the sensor would be moved at the top of the SR range what would then still have the shutter in the image?
The shutter covers the sensor in its entirety, the use of sensor shift might reduce the amount of darkening, but it will never eliminate it. And in all probability the sensor may not be blocked as much by the first curtain, but the second curtain will also make an appearance in the frame sooner than it ordinarily would. So you aren't any better off by shifting the sensor. At 1/320th shutter sync speed on my Pentax K5IIs the rear curtain covers more than half the sensor at the point where the flash fires.

QuoteOriginally posted by Anvh Quote
Style RX flashes but not the computer software so can;t do the test myself.
The Style RX flash units need the EL-transceiver RX module to allow for full computer control - the BRX flash units that have been loaned to me for professional review, come with this capability built-in. You will also need the Elinchrom USB Transceiver RX module for the computer.

Last edited by Digitalis; 06-20-2013 at 07:06 PM.
06-20-2013, 11:41 PM   #57
Veteran Member
maxfield_photo's Avatar

Join Date: Mar 2011
Location: Cincinnati, OH
Posts: 1,215
QuoteOriginally posted by pentasonic49 Quote
I don't understand the t.1 but I thought that if 1/1 full power is 1/125, then 1/2 power would be 1/250 but it's 1/900 and 1/4 power is 1/2000 ---------- 1/128 power is 1/25000, it's not linear or logarithmic.
If you graph a flash's discharge with intensity on the vertical axis, and time on the horizontal axis you would get a shape with a steep rise as the flash tube begins to glow, followed by a peak, and subsequently a long concave tail as the light decays. T.5 begins when the flash intensity rises to half way between the base and the peak of this curve, and ends when the intensity drops back below the half way point. This is how most manufacturers choose to advertise their flash durations.

T.1 on the other hand starts when the flash is only at 10% of it's peak brightness, and doesn't end until it has decayed back to 10%. The T.1 duration is important when trying to freeze motion because there's still a fair amount of light emitted after the t.5 period ends. Metz is one of the few manufacturers brave enough (or perhaps foolish enough) to publish their flash durations based on the T.1 figure, because they know people will try to use their flashes to freeze hummingbird wings and what not. On paper, it make their flash unit seem about three times slower than it's competition, but the truth is most flash guns probably have as long, if not longer, of a t.1 duration than the Metz.
06-21-2013, 01:50 AM   #58
Veteran Member
Anvh's Avatar

Join Date: Sep 2011
Posts: 4,616
QuoteOriginally posted by Digitalis Quote
I did, Actually. We know is that the shutter has to be able to cover a sensor 23.7 x 15.7 mm, so we can work from that figure give a generous 3mm -/+ clearance around the sensor to allow for the SR. As for shutter velocity, with your average vertical travel focal plane shutter the velocity of the blades is approximately 7 m/s


The Style RX flash units need the EL-transceiver RX module to allow for full computer control - the BRX flash units that have been loaned to me for professional review, come with this capability built-in. You will also need the Elinchrom USB Transceiver RX module for the computer.
18,7mm it needs to travel, it's going 7000 mm/s so it takes 2.67 milliseconds, so 5,34 for cycle to complete.
1/180 shutterspeed takes 5,56 miliseconds so it adds up.
But these still aren't hard numbers only averages and proximations at best, I've actually no idea what you mean with average speed, is that for one model???

I know, that our photos are in the Elinchrome folder says enough i hope
06-21-2013, 04:27 AM   #59
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
QuoteOriginally posted by Anvh Quote
I've actually no idea what you mean with average speed
My figure was based on an approximate estimation calculated from the distance traversed by a vertical run of the first curtain at a 1/180th sync speed, shutters that have a 1/250th sync speed probably travel a tad faster than 7 m/s.
06-21-2013, 12:04 PM   #60
Senior Member




Join Date: Oct 2012
Location: weston-super-mare
Posts: 231
Original Poster
I'm impressed, 10000 of equipment to demonstrate what I achieved with a camera worth 15. See thread 37.
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, flash, k-5, k-5 ii, k-5 iis, k5, lens, pentax k-5, sec, shutter, sync, z1p
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K5, rear curtain sync flash in manual mode, advice on what flash to buy needed! 5R7 Flashes, Lighting, and Studio 4 03-25-2013 08:12 AM
High speed sync flash with manual non-A lens? baby007 Flashes, Lighting, and Studio 45 10-23-2012 08:44 AM
Flash sync speed with On-camera flash. Tonto Pentax Q 4 04-28-2012 05:26 AM
Suggestion Rants sections Verglace Site Suggestions and Help 7 02-06-2012 08:32 PM
Is Flash Sync Speed limited by the body or flash? Reportage Troubleshooting and Beginner Help 16 09-16-2010 06:18 AM



All times are GMT -7. The time now is 07:58 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