RF20 Operation

[stephanj]

Hi folks,

It's nice to stop lurking and announce myself as another RF645 user.

Please excuse my question, I will contact Tamron for a manual. The gist is that I've picked up a second hand RF20 for a nice price but it didn't come with a manual. I'm clueless about flash usage but I'd like an idea as to whether the unit is operating correctly. Here's something of the behaviour:

Set to automatic the flash displays the film speed and current aperture along with an indication of range. The camera displays the usual information (depending on mode and ambient lighting conditions) along with a flash symbol. In program AE the exposure setting will not fall below f4 at 1/60th. The flash +/- buttons can be used to set compensation thus presumably controlling the flash to ambient light ratio.

What surprises me, and this is probably down to my unfamiliarity with flash photography, is that I'd expected more interaction between flash and camera. I expected the flash to influence the camera's choice of exposure settings in certain modes. Beyond the lower bound in program AE this doesn't seem to happen. It seems then that normal behaviour is for the flash to adapt to the camera's settings. However, with flash set to auto and camera set to manual, again there's less interaction than I'd expect. The flash only responds to changes in aperture.

Does this all sound about right?

Think I'll go off and surf for a flash photography tutorial now....

 

[Paul Swenson]

Flash exposure is based soley on f-stop. Keep that in mind. So what the flash is always trying to do (when set on auto) is put out the right amount of light for the f-stop that the camera is set at. In program (which would be the most idiot proof setting), if the flash is turned on, I'm guessing the camera will not allow a shutter speed slower tha 1/60th. Just like you I'd have to check my manual for sure. If you are shooting in a low light situation where you want to drag the shutter (shoot at slower than 1/60th) then you would want to set the camera to manual, choose your shutter and f-stop yourself.

Let's say you set your shutter to 1/30th and your aperture to 4.5, your flash will read the scene and put out enough light for 4.5, and your slower shutter speed will allow some of the ambient light to record on the film. This would be in a low lit situation such as a interior room at night.

Where the flash exposure compensation settings come in most handy are using the flash as fill, say in outdoor settings. In bright, contrasty sunlight you may want to over fill, say +1. In overcast, or shaded light you may want to underfill, say -2. Youre own taste and experimentation will come into play here.


Remember, in all camera modes, AV, TV, P or M, the flash is basing it's output on the camera's chosen f-stop. This is good for you, because you want the control, not the flash.

When the flash ( not the camera) is set on manual it is putting out a constant amount of light, no matter how you have set your camera. This would be for use with a light meter, where you want a controlled lighting situation where the flash output doesn't change.

 

[stephanj]

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Thanks for taking the time to explain Paul. It sounds like the flash is operating correctly and that I've got some learning to do. A quick query comes to mind (sorry folks if this is going off topic). If the flash aims to output enough light for the given aperture, shutter speed is important. Too fast a speed and we get underexposure because the shutter closes before flash output is complete, too slow and we get overexposure because of flash+ambient light. How do the automatic exposure systems (flash and camera) deal with this? Alternatively, how to I know where to start when selecting a shutter speed?


Ah, just stumbled across a thread on photo.net regarding this very subject. The essence seems to be that the ambient light exposure has little effect on that part of the image exposed by flash. I'll have to mull it over for a while.

 

[Nick R.]

The flash duration is too short to be affected by shutter speed, i.e. you won't cut off the flash at high speeds.

 

[Paul Swenson]

Also, I might be stating the obvious, but one of the beauties of this system, is that the camera will sync with the flash at ALL speeds, even the fastest speeds, unlike SLRs which are limited to lower shutter speeds.