Flash Meter VS Flash Guide No.

[gordon_checknita]

I have sent back a Flash Meter because it seemed to be off by +2

stops. Instead of F8 it was F4 ( compared with the flash guide No. )

I also checked it against the TTL flash of a Nikon FA and FG. It was

still +2 stops off. Further, the flash meter did not indicate a loss

of two stops for a doubling of distance. This is in a room that has

an 8 ft. ceiling, white walls and a white ceiling.

I recieved the new flash meter. It still gives the the same +2 stop

reading as the the other one using manual flash, but, on TTL flash

the accuracy is within 2/3 of a F stop.

I shot a roll of slides with the second meter using TTL flash and

checking the flash meter. The flash meter was within 2/3 of a stop of

the TTL setting on the camera. The slides looked OK. I bracketed some

of the shots. The slides seem to vindicate the flash meter accuracy

using camera TTL ...except when I use manual flash and the flash

meter settings, the exposure is OVER EXPOSED on the slides. This is

also the same distance and background as the TTL shots. Shots were

done using two different flashes of different makes. The results were

virtually the same for the two flashes. Any idea what is going on?

[lemastre]

Since you didn't note the brand and model of meter, I can't comment on the

likely quality of the item. However, meters vary in readings one to another,

though usually not by two stops. TTL metering, as I get it, reads the flash

reflected back from the scene during the exposure and adjusts the exposure

accordingly. Your handheld meter is, I assume, an incident meter that

doesn't comprehend what's reflected from the subject, but only the light

coming from the flash. Thus the reflectivity of the subject and its background

can make the result over- or underexposed a little bit. Also, in a confined

space, such as a studio, it may also see some light bouncing off walls and

ceiling. And good meters have adjustments that allow altering their sensitivity

according to the results you want to see in your slides or negatives. Forgive

me if I've rehashed stuff you're already fully aware of.

[hal_bissinger]

You are totally confused here. First off, you can't meter TTL controlled flash. Your results will be meaningless. Both your flash and camera must be in manual mode and set accordingly. Second, a flash meter reading is going to be more accurate than calculating an exposure from a guide number. <p>

You used two brand new flash meters and both gave you the same results. That definitely should suggest to you that the problem is with your technique and understanding rather than a problem with the meters.<p>

Since you don't indicate what equipment you are using and how you went about taking your measurements, I really can't offer any specific suggestions other than the above as to what you need to do.

[gordon_checknita]

Hal, thanks for your advice, but, you can meter TTL flash. TTL flash is essentially reflective flash metering system. If you use an incident flash meter reading, take off the dome of the flash meter and take a reflective meter reading at the camera position, both meter readings should be the same. If the TTL flash metering system and the incident flash meter are properly calibrated the meter and the f-stop setting on the lens should be the same when using TTL flash.

[gordon_checknita]

Hal, thanks for your advice, but, you can meter TTL flash. TTL flash is essentially a reflective flash metering system. If you use an incident flash meter reading, take off the dome of the flash meter and take a reflective meter reading at the camera position, both meter readings should be the same. If the TTL flash metering system and the incident flash meter are properly calibrated, the meter and the f-stop setting on the lens should be the same when using TTL flash or incident metering.

[hal_bissinger]

<i>...you can meter TTL flash. TTL flash is essentially reflective flash metering system. </i><p>

It greatly depends on the TTL metering scheme used and this varies from simple to extremely sophisticated depending on the manufacturer. Yes, in the end TTL flash is essentially a reflective metering system, it would have to be. However because of the way it works there is alot going on that can confuse a normal flash meter that is designed to meter simple manual strobes. <p>

1) Preflashes will trigger the flash meter prematurely and result in a grossly erroneous reading.<p>

2) The flash is quenched when the system decides that the exposure should end. This may or may not be integrated into the measurement properly.<p>

3) The system is dynamically changing. Even holding the flash meter in a different position can change the exposure.<p>

In all it is NEVER recommended that you try to meter TTL flash and I can't think of a one reason to do so. If you want to see how your meter performs put your flash and camera in full manual, select an aperture, meter the flash in front of your subject, adjust accordingly and shoot some slide film.

[adam_buteux1]

is there a book someone can reccomend about studio flash and how to meter it