Why a light meter reading is too low?

<p>I have two hostshoe flash lights pointing to a reflective umbrella type of a light modifier. One of the flashes is connected with a light trigger slave and the other is either in a slave mood or connected with the first flash through a shoe connector. The light modifier points to a white wall. I place a light meter against the wall and in the center of the light coverage. The metering dome faces to the light modifier. If I set my camera aperture as the light meter reading, a phone is way too hot and I need to step down two stops to get a proper exposure. Why the light meter reading is so low? BTW, the two flashes are old ones and they don't go pre-flash.</p>

<p>Can you post an example?</p>

<p>Are you using a flash meter? A regular incident meter won't read properly with flashes.</p>

 

<p>My light meter show was in the non-cord mode, which is for flash metering without a connection between the meter and a flash. And the meter show 100 percent of light from a flash, or zero percent from ambient light. To my knowledge, all photo light meters in the market can meter both ambient light and flash light.</p>

<p>Do you have the meter set to the same aperture as the camera? </p>

<p>ISO setting? </p>

<p>You are taking a reading of the light falling on the wall, not reflecting off it. For that, either use a handheld meter with a built in reflective meter or on some remove the dome and attach a reflective meter reading device. You don't say what you are attempting to accomplish with the bg brightness. Pure white, a shade of gray, pure black. You may need to find the difference between subject ambient and bg reflective you like but once you have it, you can quickly reproduce it. Same for gel color intensity on bg. </p>

<p>I still think you should post the example picture. Not all light meter in the market can measure both ambient light and flash but I am sure yours can. I don't want to simply write it off as you meter is in need of re-calibration. Your meter may have 2 ISO settings and you may use the wrong ISO. But I would need to see what kind of subject you took pictures of to tell you what is wrong. </p>

<p>Meant subject incident and bg reflective. </p>

<p>I don't know how to attach a photo image to a post. So, I upload related photos to my profile. The light set up are shown in <a href="/photo/18190599">this photo</a> and <a href="/photo/18190600">this one</a>. And<a href="/photo/18190618"> this one (ISO400 1/125 F8)</a> and<a href="/photo/18190619"> this one (ISO80 1/125 F8.0</a>) show the whole light source. <a href="/photo/18190601">This photo</a> shows the meter reading. When my camera setting is the same as what the meter reading says, that is ISO400 1/125 F5.6, the histogram of the photo goes straight to the right edge. Again, the meter is pointed to the light source, but not to the wall.<br /> <br /> The purpose of this test is to ensure that I can set up my camera based on my light meter reading.</p>

<p>The light meter is Konica Minolta Auto Meter V F. Monolat sold the light meter business a few years ago. The current version of this meter is <a href="http://www.bhphotovideo.com/c/product/514614-REG/Kenko_KFM_1100_KFM_1100_Auto_Digi_Meter.html">this one</a>.</p>

<p>The way you have your radio receiver working in both hotshoe mode and cable mode might cause a delay issue between the flash sync which the meter will recognise but you might not.</p>

<p>Try setting your meter to 'Multi' to measure both flashes if theres a delay between your two flash units firing. In Non-cord your meter will only measure the first flash if there is actually more than one flash.</p>

<p>If you are shooting a white wall your histogram should be to the right side.</p>

<p>If one flash isn't being recorded by your flash meter but your camera is recording it you will likely be overexposing by 1 stop.</p>

<p>You're not using the incident meter correctly. It shouldn't be pointed directly at the lights, but pointed toward the <strong>camera</strong> position from where the subject is. This is clearly stated and often illustrated in the instructions for any incident meter.</p>

<p>You only point a meter directly at the lights when you're trying to set lighting ratios, and then you shouldn't use a domed diffuser but a flat one (or a recessed dome like Gossen have).</p>

<p>Like a lot of others have suggested.<br /> Check: (1) Your camera is set manually to its X-synch speed or a little longer if using radio triggers - about 1/160th with Canons and 1/200th with Nikons. If you let the camera automatically choose a shutter speed it'll overexpose.<br /> (2) Make sure you have the same ISO set on the camera as you do on the meter.<br /> (3) If the meter readout is in decimal f-stops (Aaaaargh!), then you have to convert this to a proper F-number. Like 8.6 on the meter actually means f/10.<br /> (4) Check you haven't got a sticky aperture blade on the lens - least likely scenario. You'd notice this with ambient exposures as well as with flash.</p>

<p>Edit: Those Sunpaks have an extremely short flash duration when set to low power. I would use a P-C cable to fire the flashes directly from the meter, and not rely on the flash triggering the meter. The meter may well be missing a part of the flash output. A quick test of this theory would be to set one flash to 1/8th power instead of two flashes on 1/16; then see if the meter reading is closer to the actual exposure needed. In fact check if the meter reading corresponds with stepping the flash power up one stop at a time.</p>

<p>Further edit: If your test is just of the white wall, then of course it'll end stop the histogram to the right. That's where white ought to be!</p>

<p>Thanks Ian for your input. A very good analysis. A delay of the second flash can be a reason. The meter only has three modes: ambi, cord and non-cord, but multiple flash. So, I only can meter the first flash triggered. The wall colour is light blue. I put a close to grey colour shirt on top of a black reflector and place them in front of the wall. The histogram looks about right this time. The shirt is close to properly exposed with a litter bit overexposure. I used to set the aperture based on the main screen. 4.09 (set 4.0) in this case, but not where the aperture needle point to 5.6 in this case. That would cause the overexposure too. </p>

<p>4.09 on that meter means 1/10th of a stop below f/5.6. In short f/5.6 is as close as you can practically set the camera to the indicated exposure. That's the drawback of digital readout meters that use ridiculous decimal-stops. The exposure can be miles away from the indicated base aperture.</p>

<p>The little travelling arrow on the meter's aperture scale is a far better indication of where to set the lens aperture.</p>

 

<p>To check if multiple flash is the problem, switch one flash off and check if the flash value changes to see if that is the issue.</p>

<p>The Flash Meter IV's I have both have the Multi-Single option, I thought that maybe that was carried through..</p>

<p>that's the flash meter IV that you have. The OP has auto meter VF which would measure flash but without some advanced features of the flash meter.</p>

<p>Yeah.. ancient.. and spoilt :-) The Flashmeter's are pretty old too!</p>

<p>Just triggering one of the flashes will establish whether the overexposure is caused by any trigger delay between the two flashes though..</p>