BetterPhoto Q&A
Category: New Answers

What's best for shooting indoors?

Thanks for any help.

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June 21, 2007

You want someone to tell you what setting to use on your camera i.e. f/number – shutter speed – ISO etc. for flash photography in an auditorium. Can’t be done – too many variables however:

It’s difficult to explain how fast flash falls off with distance. Each time we double the distance lamp to subject, the arriving light energy at the subject plane is reduced 4 fold. As an example, camera mounted flash yields correct exposure at f/8 when subject is 10 feet away. Move back to the 20 foot mark and the light energy at the subject plane will have fallen four fold. Now you must open up the camera 2 full f/stops to f/4 or under exposure results. This is the basis of the difficulties facing flash photography. Indoor flash is made more difficult by high ceilings and open expanses. Walls and ceilings reflect (bounce) some light and thus most tables and camera setting aids are based on close quarters (in-house) with light colored walls and ceilings.

Sensors to the rescue: Modern cameras with built-in flash and modern portable flash units generally sport a circuit able to change the duration of the flash on-the-fly. No small feat considering how quickly a modern electronic flash fires. Generally we can’t change the brightness but we can use duration of the flash thus we can exercise control over the exposure. The sensor monitors reflected light as it comes bouncing back during the first few milliseconds of the flash. The camera is set to a pre-set to a pre-determined aperture and the sensor circuit controls exposure by extending or decreasing the flash duration based on conditions.

Without this automation we must fall back on the use of a guide number. This is a value published by the electronic flash maker. Check your manual for these values. Let’s say the guide number is 80.We gusstimate subject distance and divide this value by the guide number. Example: subject 16 feet – guide number 80 thus 80/16 =5. Set the camera aperture to f/5. If exact value is not engraved on the lens barrel, set as close as you can, in this case f/5.6.

Again, guide numbers are based on conventional surrounds. A high ceiling or dark or distance walls require the guide number adjusted downward by maybe 25% or more. Only with experience and trial and error will you become expertly at this.

Because most flash units are feeble you will need a powerful unit to cover indoor sports. Sports photographers also work by available light. This is possible if the lens chosen is quite fast. A lens with a max opening of f/2.8 or better is good, together with a high ISO setting makes this feasible. An image stabilization lens would be a godsend. Problem is, fast long lenses with IS are not cheep. Another technique is to use flash in combination with a rather long (slow) shutter. Now slow shutter translates to blur from subject movement and camera shake. This method is an acquired skill. It takes practice to lean to pan with subject movements and skill to anticipate the exact moment of reduced subject motion like the monetary pause at the top of a jump when the player is suspended between going up or going down.

The answers you seek are found in using fast lenses IS lenses – powerful flash - high ISO – flash with ambient light.

Best of luck,

Alan Marcus
ammarcus@earthlink.net.

To love this comment, log in above
June 22, 2007

You want someone to tell you what setting to use on your camera i.e. f/number – shutter speed – ISO etc. for flash photography in an auditorium. Can’t be done – too many variables however:

It’s difficult to explain how fast flash falls off with distance. Each time we double the distance lamp to subject, the arriving light energy at the subject plane is reduced 4 fold. As an example, camera mounted flash yields correct exposure at f/8 when subject is 10 feet away. Move back to the 20 foot mark and the light energy at the subject plane will have fallen four fold. Now you must open up the camera 2 full f/stops to f/4 or under exposure results. This is the basis of the difficulties facing flash photography. Indoor flash is made more difficult by high ceilings and open expanses. Walls and ceilings reflect (bounce) some light and thus most tables and camera setting aids are based on close quarters (in-house) with light colored walls and ceilings.

Sensors to the rescue: Modern cameras with built-in flash and modern portable flash units generally sport a circuit able to change the duration of the flash on-the-fly. No small feat considering how quickly a modern electronic flash fires. Generally we can’t change the brightness but we can use duration of the flash thus we can exercise control over the exposure. The sensor monitors reflected light as it comes bouncing back during the first few milliseconds of the flash. The camera is set to a pre-set to a pre-determined aperture and the sensor circuit controls exposure by extending or decreasing the flash duration based on conditions.

Without this automation we must fall back on the use of a guide number. This is a value published by the electronic flash maker. Check your manual for these values. Let’s say the guide number is 80.We gusstimate subject distance and divide this value by the guide number. Example: subject 16 feet – guide number 80 thus 80/16 =5. Set the camera aperture to f/5. If exact value is not engraved on the lens barrel, set as close as you can, in this case f/5.6.

Again, guide numbers are based on conventional surrounds. A high ceiling or dark or distance walls require the guide number adjusted downward by maybe 25% or more. Only with experience and trial and error will you become expertly at this.

Because most flash units are feeble you will need a powerful unit to cover indoor sports. Sports photographers also work by available light. This is possible if the lens chosen is quite fast. A lens with a max opening of f/2.8 or better is good, together with a high ISO setting makes this feasible. An image stabilization lens would be a godsend. Problem is, fast long lenses with IS are not cheep. Another technique is to use flash in combination with a rather long (slow) shutter. Now slow shutter translates to blur from subject movement and camera shake. This method is an acquired skill. It takes practice to lean to pan with subject movements and skill to anticipate the exact moment of reduced subject motion like the monetary pause at the top of a jump when the player is suspended between going up or going down.

The answers you seek are found in using fast lenses IS lenses – powerful flash - high ISO – flash with ambient light.

Best of luck,

Alan Marcus
ammarcus@earthlink.net.

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June 22, 2007