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Thread: Flash meter help

  1. #1
    Ausphotography Regular kaiser's Avatar
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    Flash meter help

    Hey guys and gals,

    Finally decided to go out and get a light/flash meter- Sekonik L -358.

    After doing a search and reading an old thread discussing the worth of a meter- I still have a couple of questions.

    Now correct me if I'm wrong, but do these meters still meter for 18% grey like the in camera meter?
    I realise the in camera meter uses reflective metering and the hand held version I have is an incident meter- so the reflectance of my subject shouldn't come into the equation when metering, is that right?

    Say for example Im photographing a white dinner plate and lighting with a studio strobe. Using my handheld meter- is it going to give me a reading that exposes the plate as grey and not white , like my in camera meter would? Or am I missing something there?

    Also- in the other thread, somebody mentioned taking a reading for highlights and a reading for shadows in a portrait shot. ( think it was William (Longshots)). How exactly is this done? Do you just use the recessed sensor (and not the dome part) and place it in front of specific areas around the face and meter all the lights together?

    I'd like to get my exposures and lighting perfect in camera- just need to get my head around all the theory of this meter and how best to use it.

    Previously I've been using the LCD and histogram but it takes a few test shots- and with up to 5 lights that's a few test shots and running around- hoping I can save some time and improve accuracy here.

    Cheers,

    Matt.
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  2. #2
    Account Closed Wayne's Avatar
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    I am not sure whether it meters 18% grey or not.. I know that when I use my L-358 to measure flash, I just place the meter in front of the subject, click the button and the flash pops giving the reading. You can also use cumulative setting for multi light setups. Works very well, it also will give you the percentage of flash:ambient on another setting too, which makes balancing easy...

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    Ok thanks Wayne. So what I'm getting at is say for simplicity's sake ur doing a one light simple portrait. Your subject is African with a very dark complexion. Using your incidence meter, and using the aperture value it tells you- would you get an accurate exposure? Or do you still need to take the reflectance of the subject into account and apply an adjustment for subjects that are outside of average tones ( very bright or very dark ) ?

    Cheers,

    Matt.
    Last edited by kaiser; 23-10-2011 at 1:44pm.

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    Just found this on the Kodak website:

    "How Exposure Meters "See"

    Both reflected-light and incident-light meters are made to "see" the world as a medium gray. The assumption is that most subjects, most of the time, are of average tone and reflectance. So long as there is an even distribution of light and dark subjects in the scene, correct exposure is usually as easy as pointing the meter or camera at the scene and using the reading you get. But the real world does not always present subjects to you in such a straightforward way. For example, with either a reflected-light meter or an incident-light meter, if the main subject is very dark or very light, the indicated exposure will make the subject appear as a medium tone in the picture. The result will be incorrect exposure unless you apply your own judgement to the information the meter gives you.

    Use a meter reading as a guideline rather than a dictate for correct exposure. This makes it important that you understand how your particular meter works so you can consistently get good results no matter what the lighting. The place to begin this understanding is the instruction manual that came with your meter or camera. The instructions should familiarize you with the meter's specific features, its flexibility, and its limitations. Most camera and exposure meter instructions provide the basic techniques of light measurement and mention some of the situations that may "fool" the meter. If you can't find the instructions, write to the manufacture for them."

    ...and then this, which kinda contradicts the above:

    "To use it you have to slide a dome over the metering cell, which is usually a 180 degree translucent plastic diffuser. The meter then reads the light falling on the subject from all angles. It still scrambles the reading and adjusts the exposure to produce a mid grey, but this reading hasn't been affected by reflective or absorbent subject matter and will ensure that the dark subject stays dark and a light one stays light. If you've ever seen wedding photographers walking up to the bride and holding a gadget up to her face, now you know what they were doing."

    So which is correct?
    Last edited by kaiser; 23-10-2011 at 1:55pm.

  5. #5
    Moderately Underexposed I @ M's Avatar
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    In as simple terms as I understand it.

    Set your camera at desired iso & shutter speed. For the purpose of this we will assume setting iso at the base or native level for the camera. If using wireless triggers you may be able to get to your cameras synch speed with the shutter. If using something such as the pocket wizard triggers you will be able to exceed synch speed easily. That way you control ambient light ( if there is any ) to either allow it or exclude it from the image.
    Set those values into the lightmeter.
    Having done that, get your light ( we will work with just one at the moment ) falling where you would like it in relation to your subject. Standing out of the path of the light reach in with your lightmeter and hold it at ( as a starting point ) at your subject's eyes with the difusion dome pointing towards where you will be with the camera when photographing. Trigger the light and read the resultant aperture value that the meter gives you. If you desire a tighter aperture, increase your light power and retest and vice versa.
    If you have a light that is falling unevenly on ( for example again ) the subjects face, move the meter into the shadowed areas as well as the brightest points in order to see what difference there is in exposure levels between those areas. You may find that there are 4 or more stops between one side of the face to the other with a light that is coming in at an extreme angle. You may want to then fill that dark area with another light so as to make that dark area only 1 or 2 stops darker instead of 4 or even to fill it to the same level as the main light. That is where your meter will very quickly and easily give you a good indication of the amount of light needed to fill the shadows and telling you the aperture needed to expose the main light "correctly".
    When using multiple lights, simply keep all things constant as far as the subject being in the one place goes and measure the lights individually to determine how far apart in stops each is to the main light.

    The very basic of basic lightmeters do quite an accurate job of telling you what is happening before you start shooting. You only have to remember to re meter when there is an increase in subject to lighting distance or when you adjust the lights up or down.

    Yes, dark clothing against pale skin or dark skin against light clothing will require a little fine tuning with either light power or aperture adjustment or both on what the meter tells you as it is only seeing the light coming towards the subject and not taking into account any colour or shading differences in the subject.
    Andrew
    Nikon, Fuji, Nikkor, Sigma, Tamron, Tokina and too many other bits and pieces to list.



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    Thamks Andrew. So I am I right in saying, using the default readings of an incidence meter, held in the same light as the subject - will produce accurate tones (white will appear white, black appears black)- as the reading is not being influenced by the reflectivity of the subject?

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    Moderately Underexposed I @ M's Avatar
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    The hand held meter is only reading the "flash" at the point that it hits the subject.

    For example, you have a person with average toned white skin at the brightest point that the light from your flash falls. Holding the lightmeter at that point will give you an aperture reading that should expose the subject properly as it simply doesn't "see" the subject.

    If you were to project that same amount of light from a continuous source on to your subject and let the camera meter evaluate the scene you may find that the camera wants you to shoot at a much reduced aperture to comply with the meter and exposure algorithms programmed into the camera. It is trying to do what you described and turn the brightest white parts to a neutral grey meaning that you would have to apply positive compensation in order to get that exposure as you want.

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    Thanks - clears it up perfectly - just had a few conflicting bits of information from other web pages that were making my head spin haha. It'll be a lot easier once I actually have the thing so I can practice and see for myself.

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    It's great to have a community like this to bounce ideas around and get advice. I'd like to share a link with resources that helped me understand more of the theory behind metering. It is also a great read for lighting, exposure and histograms in general.
    Light meters are just a tool, and they may not be needed for everyone - but I can see it being quite helpful for what I do.

    Lots of articles, webinars and tutorials on the link

  10. #10
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    kaiser good find on that link. Very good reading.

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    Yeah theres a good 4 pages of excerpts - and not just on metering. A lot of stuff on portrait lighting, landscapes and product photography - including an excellent article on how to light glass objects.

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