Flash Setting: auto slow sync ???

[Peter Walker]

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I'm not a flash guru and normally use flash in two situations:

• Very dark environment with a light ceiling to bounce some light into a people scene, usually with the flash exposure compensation (FEC) set to -1 or -2.  I try to use FEC to make the use of flash imperceptible.
• Bright sunny outdoors to pop a tiny bit of fill-flash into subjects faces, e.g. under a hat.  Once again I try to use FEC to make the use of flash imperceptible.

I understand second-curtain sync and flash exposure compensation.

 

What confuses me is the auto slow sync in the Flash settings menu in the SL.  I realise that, generally, the flash firmware in the SL has some issues but I would like to understand what I should be / could be doing with this setting.

 

Does it have something to do with A and P exposure mode and TTL?  Does it force the shutter speed to not go any slower than the shutter speed selected in this auto slow sync menu (or whatever the 1/F 2/F formula works out)?  So, if I had a TTL flash on the camera, and I had auto slow sync set to 1/60, even if the camera's ambient exposure calculation wanted to shoot at a slower shutter speed than 1/60, it would limit it to 1/60, thereby relying on the flash to provide the light necessary for the subjects.  

 

So, at night, with auto slow sync set to 1/60s, I would get a dark background and brightly lit subjects that the flash reached - significant difference between the ambient light and the flash light?

But, at night, with auto slow sync set to 1/2s, I would get a brighter background (potentially shake blurry) with less difference between the flash-covered subject and the background?

 

Is this right?  Or does it do something else entirely?

 

Extract from Leica SL manual:

 

SELECTING THE SYNC SPEED RANGE

The Leica SL allows you to limit the shutter speed range used in the automatic program and aperture priority exposure modes , e.g. to suit your picture composition ideas. You can choose between two automatic and several manual settings.

Setting the function

1. In the menu's CAMERA section, select Flash Settings,

2. in the submenu, Auto slow sync., and

3. in the corresponding submenu, either one of the two automatic

settings - 1/2f min. 1/60 s or 1/f min. 1/60 s, or the desired slowest shutter speed.

Notes:

• 1/f min. 1/60 s results in the slowest possible shutter speeds based on the rule of thumb for free-handed, blur-free pictures, e.g. 1⁄100s with a focal length of 100mm. On the other hand, this setting rules out slower speeds than 1⁄60s all together, i.e. even when using shorter focal lengths than 60mm. 1/2f min. 1/60 s is principally the same, except that it results in twice as fast shutter speeds whenever possible, e.g. for even more safety against blurred pictures.

• This menu item can be assigned to the FAVORITES menu.

 

 

[Jared]

If you have the camera in A or P mode AND the ISO is set to AUTO, then the slow curtain sync works (sort of). The FEC set in camera will take effect just as you would expect, and the camera will lower the shutter speed to try and keep a correct ambient exposure until you hit the minimum shutter speed allowed by the slow speed synch settings or the 1/f value, whichever is faster. If more light is needed, you will simply get an underexposed shot--the camera won't raise the ISO above 50.

 

If you manually choose an ISO other than AUTO you simply don't get a slow curtain sync. The camera wull fire the flash properly, but it will keep lowering the shutter speed waaaayyy below the value you set, basically just trying to expose for ambient as if there was no flash.

 

I understand from other threads that Leica considers this latter situation a bug and intends to change it. It doesn't match the info you referenced from the manual. The behavior in AUTO ISO basically does match the manual, except I would expect the camera to start bumping the ISO once the minimum shutter speed is reached and it doesn't.

 

- Jared

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[FlashGordonPhotography]

Flash in A and P modes on the camera is broken, badly. Leica are aware of this. (I wrote detailed lists to Leica Australia who forwarded them to Germany for me.)

 

Auto sync *may* work indoors with auto ISO, sometimes. In A and P mode the flash doesn't always fire. In any camera mode the use of a TTL flash disables exposure preview.

 

I hope it will be fixed sooner than later because currently I am using other cameras to do the work I bought the SL for.

 

Gordon

[Jared]

Interesting. I, too, have had occasional problems with the flash not firing in A and P modes but had thought it was just cycle time on a follow-up shot. I'll look more closely. Have you noticed any pattern with this particular part of the issue?

 

- Jared