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Author Topic: Slow Speed Syncro Flash  (Read 829 times)

Offline SimonW

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Slow Speed Syncro Flash
« on: January 28, 2016, 10:13:37 AM »
I'd welcome comments from Hinfrance (who I see is still using his Pentax) or of course anyone else.

What is Slow Speed Syncro Flash? It's a setting on my Pentax K-S2 which is only available in P, Sv and Av modes. The description in the Pentax instruction book is not helpful, but it is obviously not the same as fill flash (which is not a term Pentax uses). Experimenting with it in poor daylight indoors (in Av mode) it consistently gave over exposures.

Next time I used the camera, in manual mode and intending fill flash, I again found the parts within flash range to be over exposed, even with the flash power turned right down. Then, remembering the above, I switched to Av, turned off the Slow Syncro mode, switched back to manual, and all was then OK. But surely there must be an error in the camera firmware (which I keep fully updated) if Slow Syncro is in fact effective in all modes, even those where the option cannot be selected?

Simon
Simon Warren
(in Dunning, Scotland)

Offline Hinfrance

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Re: Slow Speed Syncro Flash
« Reply #1 on: January 28, 2016, 01:20:42 PM »
Hi Simon.

Slow speed sync is effectively a fill flash mode. Technically it is first curtain synchronisation that would if used on a moving subject give movement trails after the flash fires. In setting P, AV, TV and SV you can set the flash mode on the camera to 'slow' and (theoretically) the camera will expose for the background and expose the flash for the foreground. You have to have a TTL flash or the camera's inbuilt flash operating for this to work. I have tried it with the K5 and I get the correct exposure with my Sigma flashgun (EF-610 DG Super) set to PTTL and with the camera flash compensation set to -1.0. That last bit is a personal preference - I don't like the brightly exposed shots I get with the compensation set to zero.

It is noted on the Pentax forums that flash overexposure is a frequent issue when the subject is close to the camera and you are using a powerful flash. The GN on my Sigma is 61, hence my tweaking the compensation down a little, even when bouncing, close up and indoors.

Don't forget you have trailing curtain synchronisation too, which will give you the pre flash trails as the flash fires just before the shutter closes.
« Last Edit: January 28, 2016, 01:32:05 PM by Hinfrance »
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Offline Hinfrance

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Re: Slow Speed Syncro Flash
« Reply #2 on: January 28, 2016, 02:36:04 PM »
An addendum to the above for clarification.

Fill in flash in Pentax terminology is 'Daylight Sync'. This works only in P mode with the flash set to default mode. It will work with PTTL flashguns whether or not they have an A mode.

You can use the leading or trailing curtain options too, but for normal applications like people backlit by a sunset the camera P mode and PTTL flash would be the default settings.
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The theory seems to be that as long as a man is a failure he is one of God's children, but that as soon as he succeeds he is taken over by the Devil. H.L Mencken.

Offline SimonW

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Re: Slow Speed Syncro Flash
« Reply #3 on: January 29, 2016, 09:58:21 AM »
Hi Howard,

Thank you for responding. I do understand leading vs trailing curtain sync, having used both on my K10D as well as the K-S2 (vehicle light trails etc), and I've found that by choosing ISO, shutter speed and aperture (in any mode) to give a correct exposure without flash, then turning on the flash with-1 compensation either the pop-up or the Metz on the shoe, gets me a quite satisfactory fill flash result every time. My K-S2 doesn't have a setting for daylight sync mode and I didn't notice a mention of that one in the manual, but I guwss it could be automatic in the Auto and P modes (which I've very seldom even tried).

Having experimented further it seems my problem of over exposure certainly only happens with the slow sync selected, and it does seem like the flash (normally under P-TTL control) must be locked to full power whatever the compensation setting. Now I know about it I'll probably find it easy to avoid, and I'll be sure to turn it off after use.

When I had the problem in real use I was in the same village hall and same conditions I often take photos in, and with the same camera settings - there was of course no indication that slow syncro was turned on. As I said, switching temporarily to Av mode so that I could switch it off immediately solved the problem. It does appear to me that the firmware program is illogical - either the option should appear in all modes or it should not be in effect in the modes where it cannot be turned off.

Cheers, Simon
Simon Warren
(in Dunning, Scotland)

Offline Hinfrance

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Re: Slow Speed Syncro Flash
« Reply #4 on: January 29, 2016, 12:59:55 PM »
I have to agree with you that there does seem to be an issue with the firmware in either the camera or the flash. which Metz do you have? I have rebuilt my smashed Metz 58-1 with some sellotape and bits of cable tie, and although I no longer have very wide angle or the built in bounce card available it is mostly working. Using that instead of the Sigma I still get no significant exposure issues when using slow sync and switching to manual afterwards. The flash parameters page after switching to manual does not show the slow sync option, so I guess it is being turned off automatically when it is not available in the selected mode.

I have updated the firmware on the Metz, is it possible that yours is out of date or that they simply haven't got a firmware update for your new camera?
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