PTTL-HSS mode

Please, advise me. The max. synch speed of my Pentax is 1/180th sec. But in PTTL-HSS mode (Metz 58 AF-1) I can decrease the shutter speed below this amount. What is the difference between using a camera capable of 1/250th synch speed with 1/250th synch speed and using my Pentax in PTTL-HSS mode with 1/250th speed? Thanks in advance.

In short it allows you to decrease ambient light using less flash power. It also helps reduce blur seen from ambient light tat might otherwise be frozen by flash.

More explanation...
It helps to understand a bit how the shutter works in these conditions... hopefully I do the expatiation some justice...
Basically the shutter has two "curtains". One opens to allow the sensor to be exposed. A second "curtain" closes to stop exposure. At the maximum sync speed the entire sensor is exposed.
On Pentax this maximum is 1/180 second. Anything faster requires that the second curtain starts closing BEFORE the first curtain is fully opened. This results, at the highest speed, only a small sliver of the sensor being exposed at any given time.

When you use flash, the flash is much faster than most shutter speeds. So Shutter speed will not affect the exposure from the flash. You need to control that with aperture (or with flash power, but lets assume flash power is consistent for now - to make things easier).

If the higest sync speed is 1/180, recall this means the smallest amount of time possible to fully expose the sensor at one time, the flash will therefore affect the entire sensor.

Go any higher than 1/180 on a Pentax and only a small portion of the sensor will see the flash. So you will start getting a dark band on one end of the frame. The fast the shutter speed, the larger the dark band becomes.

This can be used to great effect on other camera brands, but unfortunately Pentax has crippled the camera to not allow normal flash above 1/180 second. ARGH!!!

To work around the issue of getting a dark band, you need to use High Speed flash. This pulses the flash so that the sensor sees some amount of flash throughout the exposure. Of course this means the final flash power is much lower such that multiple flashes can be produced from a single charge.


Higher end cameras will allow the sensor to be exposed down to 1/250 or even lower periods of time.
This is really nice for photographing where you want to bring down the ambient light, for example the sun.
When using flash, ambient light is controlled by the shutter. So you can decrease the sunlight to near darkness and your flash will still properly illuminate the subject .

The difference between 1/180 and 1/250 is pretty minor (1/3 stop??) and I wouldn't worry much about it, but a camera with 1/500 or 1/1000 sync speed can create some interesting images using significantly less flash power.

Even though flash may be as fast as 1/20000, the ambient light may cause the subject to expose enough to leave blur and trails. A faster sync speed helps eliminate some of the blur visible from ambient light.

I just really wish Pentax would allow the hotshoe to fire a flash with higher sync speeds. Sometimes that dark band can be used for creative control and be a desired effect!

Just to add that since the flash is pulsed (to illuminate the sensor as the open strip of shutter proceeds) the total power of the flash is normally reduced by 50%.

There is hardly any difference between 1/180 and 1/250. In fact, in some cases the Pentax has an advantage e.g. the Nikon D700 has a sync speed of 1/250 but a low ISO200. The Pentax has a low ISO100 and 1/180 - so that's about 2/3 of a stop better for the Pentax

But HSS mode allows full fill-in flash outdoors. Works really well

Matt

The Pentax AF 360FGZ and AF 540FGZ will sync at any shutter speed in HSS mode,I used it at 1/4000th sec on my K10D. Page 84 of the AF540FGZ gives the Guide Numbers up to 1/6000th sec but i have tested my K7 at 1/8000th sec and it works! However the light output is greatly reduced but it`s fine for fill in flash which is what the Manual recommends that you use it for.

Best Regards - Pete.

Thanks. But are you sure it really synchronizes the flash? I mean really sets the appropriate amount of light to the correct exposure or just release some prefixed or available amount of light?

Best Regards - KZ

It's the correct amount.

G

Absolutely! I have used it with both K10D and K7 it even works in Wireless Mode.
As i said the Manual states that the sync is unlimited and gives the Guide Numbers for Combinations From 100 iso to 400iso and shutter speeds up to 1/6000th sec (Pre K7)and i have taken a couple of test shots at 1/8000th sec just to see for myself. The Manual does state that it is meant for use as Fill in Flash (Which is what i use it for) but it does Sync perfectly.
The 1/180th sec only applies to the in built flash or non HSS Flashes.

Can I assume none of this works on a K100 ???
(must buy that K10 !!)

Sorry to disappoint you but it also works on the K100D I believe, if you have the right flash that is.

It's so far as I know only very useful as filling flash, besides that I don't know any use of it.
If you want to freeze something you're better off using the flash normally instead of using HSS since a single flash freeze the image but with HSS it "strobes" so it won't stop movement.

That doesn't disappoint at all !! Quite the opposite

I assume I need a Dedicated flash ?? AF 360FGZ or AF 540FGZ ?

Correct. And possibly the Metz as well.

G

How is this done ? the camera won't let me set less than 1/180, so how is this acheived ?

Here is a good guide for you link

It won't let you set MORE than 1/180 (other than in HSS mode), but you can set less. By more, I mean 1/250, etc.

G

Edited: Ignore me. I'm talking complete nonsense.

To start it only work on the newer Metz guns (except 36 AF-4) and it's a mode on the gun itself.
If you set the gun on HSS it should allow your camera to use faster shutterspeeds, don't know if there is any camera mode restrictions though, don't believe so besides that you can't use it in X-snyc mode and B