Confusing flashes

tr0gd0o0r · Feb 15, 2004

Could someone to operate an external flash properly? I've never really been taught how to do this and I've started playing with it a lot lately. Here's my set up. I have a istD which supports a wireless connection w/ my external flash. So i'm using two point lighting. I've got the internal flash and the external. I'm using p-ttl metering for the flash. I've been just letting it do its thing but its been giving me some extremely bright results (coudl this be the product of shooting under/over the sync speed) any info would be helpful

ksmattfish · Feb 15, 2004

Assuming that you have a focal plane shutter (I'm not real familiar with the *ist), if you shoot over the sync speed with a flash only part of the image will be exposed to the flash.

My experience with recent model 35mm SLRs with the pop-up flash is that they don't do a very good job figuring out 2 point lighting, even when they have that exposure setting. Most of my experience would be with Pentax cameras.

Osmer_Toby · Feb 16, 2004

hmmm. not familiar with pentax, but i agree with the above re: internal flash. are you set up such that the internal can act as master, or is it just a triggering device? i.e. does the cam automatically calculate settings and communicate them to the other flash unit? if not, both could be firing at full strength (which isnt much for the internal, anyway). also, are you firing the external into an umbrella? if not, you probably want to invest in one, cause they make all the difference in the world.

tr0gd0o0r · Feb 16, 2004

ksmatt - the ist must have something like you are talking about, because it has a high speed setting on the flash so i can fire off at whatever shutter speed I want to ( i normally completely ignore my in camera meter tho and fire at whatever its set at because the meter is wrong anyway w/ the added flash). The process I'm doing right now is sort of test and see. I take a shot and if its under exposed change the shutter speed or aperture accordingly. DO you think actually using the sync speed might help the exposure be closer?

Osmer- Yeah the internal asts as a master (I can't figure out how to get it to work any other way even though I really would prefer it) I think the camera figures up the settings and sends it to the flash but I'm not sure. No, I'm not firing the externalinto an umbrella. It wouldn't be a real practical set up anyway. I'm using a flash that is designed to attach to the hot shoe but conveniently works w/ the camera wirelessly, so it would be hard to get that set up working, plus i don't have the money to put into an umbrella right now.

marksw · Feb 17, 2004

The camera will have an X-Sync speed, probably 1/200th or 1/250th of a second. This is the (fastest) speed at which you should fire to get the most power from your flash. The flash is fired as a short burst at the point that your sutter is fully open.

If you use the high speed sync (FP Flash) then the flash has to fire for the duration of the exposure so that all the film gets exposed (preventing a narrow exposed slit as ksmattfish described). This means the flash has less effective power, and may well result in under exposure.

I would suggest you work at the X-Sync speed or slower while experimenting. I hope this helps a little

Big Mike · Feb 17, 2004

I'm no expert but as far as I know...when you change your shutter speed (within the sync limits) when using a flash, you only change the amount of ambient light hitting the film/sensor. You will still get the same amount of flash exposure.

The correct thing to do is to set the shutter speed at your sync speed or slower and adjust the aperture (or the flash) to get proper exposure.