Fill flash with Canon FD

[trw]

I'm having a little trouble understanding manual fill flash, so please

let me know if this sounds right....

 

Say it's a bright sunny day and I'm shooting 100iso, so I want to use

1/100th, f16. If I want the flash to make the shadows 1 stop under the

highlights, I set the film speed dial on it so that f11 matches the

distance to my subject, and set the switch to auto mode?

 

Why isn't the sensor then overwhelmed by the direct sunlight shining

on it?

 

(assume the flash is a Vivitar Auto Thyristor 2800, if it matters)

[alan_chan4]

I don't know about your flash, but often the ISO setting of old flashes does nothing but for displaying only. If you want to achieve fill-flash, set the aperture setting of the flash 1 or 2 stops larger than the setting of the lens. If the lens is f16, the flash should be f11 or f8. Usually 2 stop difference is more pleasing because you want as little visible flash effect as possible.

[trw]

And what if there is no F-stop rating on the flash?

 

I found a method online that uses the guide number and some math...

 

It looks like the AE1-P syncs no faster than 1/60, so I'd have to use f22 in bright sun, so two stops difference is f11, so (the 2800's GN is 80) I'd have to be about 7 feet from the subject. Which would make it difficult to use a portrait lens for anything other than head shots.

 

So basically to use fill flash in bright sun I either have to get a flash with a MUCH bigger guide number or use one of my leaf-shutter cameras so I can sync at higher speeds. I'm not too keen on tryng to handhold a TLR or press camera and a flash at the same time.

 

If I use two flashes (one hotshoe, one on a flash bracket), how do the guide numbers add?

[kerkko_kehravuo]

I have used New F-1, FDN 24 mm 1:1,4, FDN 50 mm 1,2 and FDN 85 mm 1,2 and Metz 60 CT-4 with success. These lens stop down only to f:16, so ISO 50 or IS0 64 film is needed in bright sunlight and then again the most powerful flash unit is required. Easy with some training.

 

Kerkko K.

[chris_waller]

First set your camera's shutter-speed to the flash-sync speed or slower, e.g. 1/60 th. Now, meter the scene and set the aperture. Then, on your flash-gun set the film-speed to whatever film you have in the camera and then set the range-selector to whatever covers the aperture set on your camera. (On my Vivitar 283 I have four ranges indicated by colours - yellow, red, blue, purple corresponding to four different aperutres). Now, change the film-speed on your flash-gun to two stops faster than the speed of the film you have in the camera - i.e. if the film in your camera is 100 ASA then set the speed on the flash-gun to 400 ASA). Then you're set to shoot.

[alan_chan4]

I checked the spec of your flash and it should have f2 & f4 setting in AuTO mode. That means your lens and camera should use f4 or f8 and 1/60s in fill-flash situation. There are 2 things you can do if you found the aperture was too small - 1) Use lower ISO film, 2) Use ND filter on the lens. The math for manual fill-flash is (GN = aperture x distance / 2). If you need to know the GN of 2 flashes combined, it will be [square_Root(GN1 x GN1 + GN2 x GN2)]. However, if done right, you will discover the trick to fill-flash is smaller GN, not higher.