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12-02-2013, 05:16 PM   #16
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QuoteOriginally posted by kenyee Quote
The only use case is outdoors in daylight when you want to lower the ambient so your speedlight is more useful..
But if you are using your speedlight for say, fill lighting, doesn't it still end up having a darker band if your fill is only captured on one part of the sensor?
What is the specific use case where you are using your speedlight and it is not impacting the exposure?
Really curious.

12-02-2013, 06:22 PM   #17
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QuoteOriginally posted by crewl1 Quote
But if you are using your speedlight for say, fill lighting, doesn't it still end up having a darker band if your fill is only captured on one part of the sensor?
What is the specific use case where you are using your speedlight and it is not impacting the exposure?
Really curious.
Yes, but the point is, you deliberately crop out the dark band. So back up a bit when framing (plan to crop the band in post), and you have a bit more control over darkening the ambient...
12-02-2013, 09:43 PM   #18
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QuoteOriginally posted by kenyee Quote
The only use case is outdoors in daylight when you want to lower the ambient so your speedlight is more useful...
Hmmmm...the conventional way of doing this is to use a leaf shutter lens or ND filters. The reason being is that above the X sync speed, the full frame is not fully open at one time. Perhaps a few bullet points would be helpful.
  • The flash fires at the point in time where the leading curtain completes its travel
  • At speeds greater than the sync speed* this results in flash light only illuminating part of the frame. With a vertical travel shutter moving top to bottom, that would be the top of your composition when using landscape orientation.
  • At twice the sync speed, only the top half of the frame has flash illumination. At 4x the sync speed (1/720s) only the top 1/4 of the frame will be flashed. At 1/1440s, 1/8 of the frame and so on. The second link you provided demonstrates nicely the decreased real estate at 2x the sync speed.

Given the case where you want an environmental portrait of a bridal couple with limited DOF and flash as key and fill for the subject...
  • Ambient light provides for a proper exposure of the setting of 1/2000s at f/2
  • Adjusting the flash output allows for proper exposure at a flash duration of x number of milliseconds for the subject
Make the exposure both with and without flash and note that the photos are identical except for a thin band at the top or side, there is no key or fill lighting. Cropping is not really an option.

Solution? A larger sensor would provide the limited DOF at a more moderate aperture. That is part of the traditional advantage of medium format for professional portraits. Or...simply use a ND filter with your smaller format camera.

I would say that having a setting to enable shooting at faster than the x sync speed would provide little utility. OTOH, I might imagine that the number of troubleshooting inquiries to this site regarding light/dark banding with flash would skyrocket.


Steve

* As noted in the second article you linked to, the actual sync speed may be somewhat faster than the documentation. The examples posted there with the Nikon shutter also seem to indicate stepped speed for actual shutter curtain velocity for higher speeds. My examples assume a true maximum of 1/180s on a Pentax dSLR and a fixed curtain velocity.

Last edited by stevebrot; 12-03-2013 at 02:22 PM.
12-02-2013, 11:47 PM   #19
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Given I can deliver 100% flash illumination @25m 1/500 iso400 in HSS with enough reserve to allow multiple flashing @ about 2/s (using tr3)
What is the point of hacking the 1/180 speed in some kind of bodge up that wont work well anyway.?

12-03-2013, 02:12 PM   #20
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QuoteOriginally posted by awaldram Quote
Given I can deliver 100% flash illumination @25m 1/500 iso400 in HSS with enough reserve to allow multiple flashing @ about 2/s (using tr3)
Actually, HSS isn't very efficient...100% flash illumination at probably 1/5 of max output (depending on your HSS shutter speed) of the flash is roughly what it puts out. It's a balancing act.
If you use PW TT's Hypersync, you probably get 1/3 of max output of a studio strobe which is higher than a speedlight.
All these options and the X-Sync thing are various ways to control ambient (but HSS/Hypersync also lets you use narrow DOF).

p.s., the default for the menu option enabling shooting beyond 1/180 sync would be OFF. It wouldn't be enabled by default like Canikon/Oly/Sony do...though of course that begs the question of whether Pentax thinks its users aren't as smart as Canikon users because this is locked out currently
12-03-2013, 03:35 PM   #21
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QuoteOriginally posted by crewl1 Quote
But if you are using your speedlight for say, fill lighting, doesn't it still end up having a darker band if your fill is only captured on one part of the sensor?
What is the specific use case where you are using your speedlight and it is not impacting the exposure?
Really curious.
It depends what kind of flash you are using. If the flash pulse has a duration longer than about 1/120 of a second then you could shoot at any speed - even 1/8000 - and not get any banding. You might get a slight variation in exposure from top to bottom of the frame but that's easily correctable in PP.

Now the question is probably what sort of flash would have such a long flash duration?

There are three I can think of.

1. Studio flashes - the more powerful ones sometimes have a rather long duration, sometimes longer than 1/100 of a second.
2. LED based flashes
3. The old style magnesium flashes - such as the disposable flash cubes and flash bulbs which used to be very common
4. Possibly third party non-dedicated flash gun with user selectable duration
5. A home made flash designed specifically to have a long duration.

Some of the more powerful studio flashes achieve their 'power' by keeping the lamp illuminated for a longer time apart from just using a more powerful bulb. This allows to keep down the cost of the bulb which increases exponentially if one has to keep a very short flash duration.

The LED based flashes as used in cellphones and some P&S cameras always have a rather long duration - this is actually a limitation of current LED technology that limits how much energy you can put through an LED in a short time without blowing it up. While it is usually a limitation it can actually be very useful for macro photography allowing you to shoot with flash at high speed even in sunlight. The low power however limits this only to macro applications and not much else.

The magnesium flashes are still available from surplus stocks and can sometimes be very useful and can give some extremely powerful and long bursts of light. They are of course one time use so you have to prepare your shot very carefully. The problem with these sometimes is that the flash can actually start a bit late and take some time to ramp up so you might end up with the first part of the exposure being dim.

I see no reason why there shouldn't be generic HSS flashes available, and probably there are and I just don't know about them. A third party generic flash could easily be made with manual controls to select the flash duration in exactly the same way as dedicated HSS flashes do automatically.

Although I don't know of any generic HSS flash I do know of something similar that is homemade, because I actually made one myself. Well sort of because it is still a prototype which doesn't lend itself to being cariied around so I've only tried it out at home. I can regulate independently the capacitor voltage and the duration of the burst and have managed to achieve even 1/50s bursts. If I can do it at home I'm sure any major flash producer can do it much better.
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