Hi, I admit, I'm a dummy, but I have a number of questions I'd like to see answered before I buy one. I almost never use a flash, only in some occasions when I use the pop-up on my Minolta 7xi. I'm interested in using flash in backlighting situations or as fill-up etc. but I think of buying a flash with a movable head so I can finally get rid of those red eyes. In my childhood I used a flash on a fully Manual camera and I had to verify on the flash back which lens opening I should take in order to get a good frame exposure. Now I'm wondering how this works on a fully automatic camera, I mean, how does the camera know how much light the frame will get after firing the flash? Is there some communication between flash and body? If so, is it safe to buy a third party flash such as Vivitar? My old flash (mid 80) has a thyristor in it and it measures the ambient light and changes its power accordingly but I'm sure that it does not communicate with my camera body in any way. So how does these new flashes work, or wasn't there any evolution? I've noticed that flashes are also sold (camera's too) with a special connection to connect a wire to the flash. Is this the feedback channel or is it only to use the flash remotely? Recently I bought a medium format (645) and found out that my old flash fits nicely on it (cheers) but I haven't taken any pictures with it yet. On the 645 the light metering works like my old manual 35mm, it meters the light for me and then allows me to take the picture. In order to take pictures with a flash I had to put my old SLR to 1/125 sec. while my 645 has a max. sync speed of 1/60 sec. (whatever that means?) Does this mean I have to put the shutter speed to 1/60 s each time I take a picture with flash? Does this have any effect on the aperture I have to use on the camera? The table in the back of the flash just lists a table of distance versus aperture seetings. Is this table then valid for both my 35 mm and 645? More info: the 645 is: Mamiya 645e and my old flash is: Topca 325CS.

Thanks!! Tom

-- Tom Bruns (worst101@yahoo.com), December 23, 2001

Answers

"...how does the camera know how much light the frame will get after firing the flash? Is there some communication between flash and body?..."

Yes, the flash & camera body do communicate. You'll notice that your 7xi has several contact pins in it's hot shoe. On most modern cameras the center pin does what it allways did - fire the flash. Of course newer Minoltas have a different shape of flash shoe/foot arrangement but they still have the center pin and also have extra pins to do the communication stuff. The camera body now houses the flash meter intead of putting it in the flash like your thyrister unit. This meter measures the flash through the lens and tell the flash when to stop. (This is very fast. Almost always less than 1/1000 sec.) So if you use a wide lens or a long lens, only the picture area gets metered. It's called TTL flash metering.

Buying a third party unit that is dedicated to work with your 7xi is safe and they will use the camera's built in TTL flash meter. There may be other good reasons to get a Minolta flash though.

The special connection is probably just a PC connector (Can't remember what PC stand for. Something like "Prontor Compur" though). That's just a dumb connector. It'll fire the flash, but unless the flash has some sort of metering sensor built in, it'll just fire in manual mode, usually at full power.

"...Does this mean I have to put the shutter speed to 1/60 s each time I take a picture with flash?"

Yes and no. You can use any shutter speed up to your max sync speed, but nothing faster or one of your shutter blades will start to block out part of your picture. The higher the speed, the more gets blocked out.

"Does this have any effect on the aperture I have to use on the camera?"

Not really. Flash exposure is not really effected by shutter speed as the flash duration is much shorter than your shutter speed. So, with a manual flash system you control your flash exposure with your aperture and then set a shutter speed that will control the background exposure. Usually that means that if you use a fast shutter in a dark area the background goes black but the foreground is exposed by the flash. But if you use a slow shutter, some of the background starts to show up. The slower the shutter, the brighter the background.

With a modern TTL flash system, the shutter speed will still control the background exposure, but changing the aperture will usually not effect the flash exposure, since the built in flash meter will just compensate for it.

That's just the start of the explaination and there is lots more to learn. I suggest you get a good book on the subject.

-- Jim Strutz (j.strutz@gci.net), December 24, 2001.