Old skool flash GN question.

[simon ess]

I'm using a Nissin flash on my Olympus Trip 35, using guide numbers in the normal way.

Absolutely fine, results as expected.



But...

I'd like to bounce the flash off ceilings and walls to soften the light.
If I use the correct power setting for the total distance, flash to wall + wall to subject, there is not enough light.
I guess this is due to dispersion or something.

Is there a rule of thumb for how much extra power to use in these circumstances?

Thanks very much.

 

[mike weeks]

ceiling height etc. means that a single rule is not easy to generate, this is where a light meter comes into its own

Mike

 

[simon ess]

Thanks Mike.

I had a feeling that might be the answer.

I do use a light meter where circumstances allow, but this was about casual grab shot type situations.

 

[Phil V]

Thanks Mike.

I had a feeling that might be the answer.

I do use a light meter where circumstances allow, but this was about casual grab shot type situations.

That's why we use ETTL in dynamic situations.

The calculation would need to be accurately based on flash power (differs with zoom setting) distance to bounce surface + distance from bounce distance to subject, then take into acct the light loss for the bounce surface colour and texture.

If you seriously want to do that, the best method is to do what ETTL does, use a rest flash and then alter the power based on the result.

Of course you can't do it at the speed the camera can, but with practice you'll be able to do it as accurately.

 

[simon ess]

Thanks Phil

then take into acct the light loss for the bounce surface colour and texture.

Yeah, that's the tricky bit.

use a rest flash and then alter the power based on the result.

Film camera and lack of patience.

 

[Phil V]

Thanks Phil

Yeah, that's the tricky bit.

Film camera and lack of patience.

Flashmeter (or test the setup with digital).

Though with film we always used auto flash on the run. I'd never attempt to calculate or meter flash on the run.

 

[Phil V]

And an old auto flash is really cheap if you can find one.

 

[simon ess]

Thanks again Phil.

Is that an option on an Olympus Trip?

 

[Phil V]

If you've got a hotshoe or PC sync socket it'll work.

I used one on Chinon, Canon and Bronica, and Practika too.

 

[HoppyUK]

Old skool rule of thumb was distance from flash to ceiling, plus distance from ceiling to subject, plus one or two stops.

Assuming a normal height white ceiling, if I was standing up (ie closer to ceiling and therefore less light spread) I'd add one stop. Kneeling down or with a higher ceiling, add two stops. And maybe another stop for luck! It's very hit and miss: you can calculate till you're blue in the face but there are wide variables and every situation is different.

In typical social situation, I'd be shooting colour neg film that is very tolerant of over-exposure. With slide film, I'd just not risk it without a meter.

 

[simon ess]

Thanks Richard.