Why does my SF24 flash allow me to set the aperture on the flash unit in TTL mode?

Dear friends,

I have searched the forums but can't find an answer to this.

I set my SF24 flash unit to TTL and attach it to my Leica M7 just fine. I have had some very overexposed shots in my forst few rolls of film. I was setting to TTL mode and ignoring any settings on the flash. The only thing I checked was that the exposure compensation was set to 0.

With some fiddling I discovered the SF24 flash unit allows me to change the flash setting on the flash when it is set to TTL mode. This is baffling as I understood that the camera measured the light coming through the lens and then cut the flash off when the correct amount of light had travelled through. Thus, when in TTL mode, aperture should be irrelevant. I've read the instructions to the M7 and the SF24 and they don't clarify this for me. It seems to me that 'A' mode and TTL are the same if I have to tell the flash unit what aperture I have my lens set to.

Could anyone tell me what I should be setting my flash to? Should I set it to TTL mode and set the aperture on the flash unit?

Thank you very much!

Baffled of Melbourne

From Leica's website

Do not know if this helps or not, but the flash will work on all Leica's because of this feature. Below is a cut and paste of the description. http://us.leica-camera.com/photography/m_system/accessories/flash_unit/2212.html

Go here for instructions. Dead Link Removed.

It sounds like you are using it right, it should work. Are you adding exposure compensation?

From Leica's website.

The Leica SF 24D electronic flash unit is designed to be compact and also to provide the maximum distance between the flash reflector and the camera lens, which minimizes the risk of red eye when photographing people and animals. With the Leica M9, M8.2, M8, M7 and M6 TTL the light output is controlled by its TTL flash exposure meter; with other Leica M models it is controlled by the automatic flash itself. In automatic mode, six automatic flash apertures 2.0/2.8/4.0/5.6/8/11 are available. An override switch allows the exposure to be varied by plus/minus three stops. All settings and other information are legibly displayed on the Leica SF 24D's illuminated LCD. These include an exposure confirmation indication and flash ready light which are simultaneuously displayed in the viewfinder of the Leica M9, M8.2, M8, M7 and M6 TTL.

What does your flash need to know before it can say, "That's just enough light to do the job. I can stop now?"

(1) It needs the speed of your film. Set your ISO on the flash to match what you've got in your camera.
(2) It needs to know what is the maximum distance you want your flash to cover. Select from table on flash to match distance and f stop.
(3) Finely it needs to know you have matched your f stop on your camera to one you choose on your flash.

Now Compose, Focus and shoot. Enjoy!

You can use it on TTL/GNC mode like you did. The M7 sends ISO information to the flash. You need to set the aperture to match what you set on your lens only to allow the distance range displays correctly. You're right the aperture is irrelevant for actual exposure. It's only for the display of the distance range.

SpunkySpine said:

What does your flash need to know before it can say, "That's just enough light to do the job. I can stop now?"

(1) It needs the speed of your film. Set your ISO on the flash to match what you've got in your camera.
(2) It needs to know what is the maximum distance you want your flash to cover. Select from table on flash to match distance and f stop.
(3) Finely it needs to know you have matched your f stop on your camera to one you choose on your flash.

Now Compose, Focus and shoot. Enjoy!

Click to expand...

In TTL it only needs ISO and in the M& the camera provides that information to the flash

To work correctly with M7 automatically, the SF24D must be set to TTL.
The M7 shutter must be set to AUTO.

The flash tells the M7 the correct shutter speed and the M7 tells the flash the ASA of the film in the camera IF the DX film speed is set to anything differently than is in the camera, that is the film speed sent to the SF24D. The inner dial in the back of the M7 sets the film if in any position other thsn 0 alignment with the ASA compensation. The outer dial, compensation does nothing with the SF24D.
The ISO button on the flash simply shows you the ISO the M7 has told the flash and has no effect in TTL.
The middle button on the flash allows you to select an aperture and view the distance range for an aperture. It has no effect on the flash. You do not hav to set an aperture on the flash nor have any agreement between the SF 24D and M7 as to aperture.
The last button on the left with /P allows compensation to be set on the flash and will affect exposure.
So to summarize, for proper operation set the flash to TTL, the M7 to AUTO.
When you turn both ON, you should see the correct ASA displayed on the SF24D.
Do you have a manual for both your SF24D and M7.
Information on using the SF24D is contained in BOTH manuals.
Read them.
It's a very simple system with the flash in TTL and M7 in AUTO.-Dick
BTW, the flash offers two additional modes, A, where the sensor on the flash determines exposure and M which is the traditional method. With the M7, these modes are not required.

Welcome to APUG Simon.

The overexposure might be due to:
- dirty or oxidised contacts on flash or camera;
- subject was too near | flash too powerful | film too fast | aperture too open, so to say, so that even the minimum flash duration gave you too much light. In that case, if your flash can do it, you will overcome the problem by using the flash at half power or at "winder" position.

Contacts can be cleaned with a pencil eraser (or pen eraser, which is rougher) or alcohol, applying friction with energy. Seize the occasion to clean the battery compartment contacts as well.