Manual flash photography, could use some help

Compaq

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I'll try again and post it here, I really could use some help.

I've got this old Vivitar 2500. I think it will do most of what I need. I'm planning on using it for indoor lowlight conditions, as well as the frequent fill-light snapps or whatever.

Apparently this unit has four settings, a red, a blue, manual and some triangular thing that I think is full auto or something. I'm planning on learning to use it manually.
For low light indoor shots, here's what I've tried when I mounted it on a 450D. (Bounce flash)

- check my subject distance (had to guess, they don't put the ranges on cheap modern lenses)
- so I check the chart on the back (having set correct ASA/ISO), and set the aperture recommended
- I then consider the new flash-to-subject-distance (roof-to-subject), and try to guess how much light that has been lost according to that delta-distance^2 rule
- I also take into consideration that the bouncing surface is re-emitting the light, and so more light is lost.

I experimented with this on the digital camera (so that I can check the exposures). Doubling the distance to the subject, and compensating two stops actually works :lol: Fun to see that. As for light loss due to bounce, I experimented that two stops seemed enough (white roof, not very shiny. subject distance from two to 4 meters).


Soo, that would mean that in many situations around 4 stops compensation for bouncing the light and the longer distance is necessary for a correct exposure. That is a lot of stops, hehe. Is this other's experience as well? I'd like to know these things before I start flashing away on film.

Thanks for any help!
 
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bazooka

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Bouncing eats a lot of light. You have to take into consideration not only the distance from the ceiling to the subject, but the flash to the ceiling as there is light drop off there as well as any in any other situation. Plus, the ceiling itself absorbs some of the light even though it's white.

Personally, I don't get into the numbers. I just feel it out. Basically, if I'm outdoors during the day, I use full power and possibly multiple flashes per stand as I usually want to underexpose the background.

In normal circumstances I set the flash initially by my settings... if I am exposed for low light (say 2.8, ISO 800), I set the flash on low power. Medium light (f/5.6, ISO 400), medium power, etc.... that way I'm close. I can then adjust the power. change light to subject distance, or adjust aperture/ISO along with shutter speed depending on what a test shot looks like on the lcd and histogram. And with the power of raw processing, you can easily make up 1/3 of a stop in exposure error. For me, that's the most efficient way to do it.
 
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Compaq

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Oh, didn't think about light loss from flash to the roof, thanks for pointing it out!

I can't adjust the power directly on this flash unit. When it's in manual, I have one power to use, although there are two other modes with lower power settings for other uses (close to subject). I'm sure experience is key, as always, but until then I'm analyzing the numbers, lol :)

When it comes to fill flash, here's what I believe to be smart:

- focus and check the distance to subject
- set the aperture as suggested from the chart
- take a spot reading of the background
- set the shutter speed as to expose properly for the background

will this actually put too much light on the subject? The point is to only fill in some of the shadows, but I fear that here I'm fully exposing the subject. If I then just drop the aperture about one or two stops, would that work?
 

bazooka

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That or the ISO. But those will also affect the ambient exposure so you'll have to compensate by going the other direction with your shutter speed.
 
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Compaq

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vtf, I've read that, but it doesn't really cover manually exposing properly. I'm just interested in knowing the "thought flow" of how to set it. Once I know that, I can experiment.

How do you "think" when you're setting your flash?
 

tirediron

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The "thought flow" really comes down to being familiar with your gear. Spend an afternoon experiementing. Place your camera on a tripod and set up a subject say, 15' away. Do a set of exposures starting on full power, and reducing each time 'til you're down as low as the flash will go. Move 2-3 feet toward the subject and repeat. This will give you an idea of what ditance and what power setting you need to acheive what degree of illumination.
 

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You need to frame you though process this way: "Is this a 1-stop bounce? Or a 2-stop bounce? Or a 3- or 4-stop bounce?" For example, inside of a low-ceiling boat, cafe,diner, or apartment, at close distances, a bounce is often just a 1-stop loss. And so on.

On flash units that have zoom function, MOST of the instruction manuals I have read suggest setting the flash's zoom function to TELE, to concentrate the beam so that it makes the "throw" more efficient...that can be a good way to go in larger rooms, but at times, at closer distances, it actually works better to bounce the flash with the zoom head set to Wide, or Normal ranges.

As to the success/failure of bounce flash: one of the single biggest problems is exceeding the range of the flash. Most better, older flash units had a confirmation system, when which you pressed the Open Flash button (ie, the Fire! button), if a sufficient quantity of light returned to the sensor on the flash to make a proper exposure at the settings in use, a small light would light up. Sometimes this is called the pre-flash test, or something like that. THAT IS THE KIND OF THING THE INSTRUCTION MANUAL will tell you!!!!

Anyway...ISO setting is a big,big,big part of flash and bounce flash. With older, non-dedicated flashes and cameras, the ISO/ASA value of the film, and the flash, can be set identically, or differently. So there ISO/ASA setting of the camera and the flash can be shifted, in order to get the right exposure: If you have 400 ISO film, and have a two-stop bounce, then use the suggested settings on the flash for ISO 100 film,when working in a purely manual exposure mode.

In the AUTO mode, the biggest problem with smaller flashes like the 2500 is running out of flash power when the bounce is made in a bigger room, so ISO 400 film is very,very useful.
 

vtf

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Oh, understood
I took some shots with mine yesterday and was bouncing it off 9' ceiling with a second ocf. The settings were 1/160, f4.5, iso 100. The background was black/dark. I imagine you would need to lower the shutter speed to 1/60 or widen the aperture using only one flash. But I use digital so I'm not worried about the using of film like you would be.
 

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