flash meter with multiple strobes

[RRitch]

I just bought a polaris flash meter and 2 interfit 150 lights. I have been playing with them trying to get the metering correct. I am using one of the 150s with a 24" softbox as the main and the 2nd 150 with a white shoot through as the fill. When I just the main, I get f8. The fill light is metering f5.6. When I meter the two together I get f9. My question is should I set the camera for f8 (main reading) or f9 (combined reading)? Thanks in advance.

[Lotto]

F9. Then look it up in the computer to see if your camera agrees with the light meter. The meter might need a little calibration in some cases.

[RRitch]

how do you calibrate a meter? The one that I bought has nothing about that in the manual

[Lotto]

Different meters do it in different ways, see user manual for that. But if your shots are consistently underexpose by 2/3 stop, you can also just bump the ISO down by 2/3 stop on the meter.

[TMR Design]

Are you asking about the process for meter calibration or how to specifically program an calibration offset for your particular meter?

If there is nothing in the manual then it may not have the ability to store an offset, in which case you just determine the offset and apply it to each meter reading or as Lotto suggested, set your ISO accordingly to compensate and then you don't have to think about it.

[RRitch]

Rob,

I looked at the manual again, and there is a way to program an offset. So I am assuming that if the readings are resulting in over exposure that I would dial in a negative offset to calibrate the monitor, i.e. if they are 1/3 stop overexposed I would set a -/13 offset on the meter.

[jcolman]

The quick way to calibrate your meter is to set up your camera and light (one light, not two) and shoot a white towel or cloth. Adjust your aperture until the white just begins to blow out on your histogram then back down 1/3 stop. Adjust your meter until you get the same aperture.

[TMR Design]

The quick way to calibrate your meter is to set up your camera and light (one light, not two) and shoot a white towel or cloth. Adjust your aperture until the white just begins to blow out on your histogram then back down 1/3 stop. Adjust your meter until you get the same aperture.

I would not recommend this method, as you have no way of knowing the exact color/shade of the object used. Using a meter shouldn't be a 'rough' guess. If that were the case then you may as well just chimp and adjust.

Using a hand held light meter is a way to nail the exact exposure and meters, whether hand held or in-camera, are based on a percentage of gray. Even that will vary from manufacturer to manufcturer.

The recommended method for calibrating a light meter is to use an 18% gray card. This is not to be confused with a WhiBal or other white balance targets which have equal amounts of red, green and blue, but are not usually 18% gray. For exposure we base everything on 18% (middle) gray.

So, grab an 18% gray card. Light the card evenly so that wen you take a reading (at this point it doesn't matter that the meter is not calibrated) you get no more than 1/10 stop variance across the card. This should be very easy with a small card. Now set your camera to manual focus so that the AF doesn't go crazy and hunt, fill the frame with the gray card and take a shot.

Now that that image and open it on your computer in a RAW editor. It's very important that your RAW editor not have preset adjustments applied. For instance, ACR and Lightroom have some default brightness and contrast settings that alter the histogram upon import. You don't want this to happen. So once you've determined that your editor has been 'neutralized' then look at the histogram. An 18% middle gray frame will show a center spike in the histogram.

If the spike is dead center then your exposure is perfect. If the spike is left of center you're underexposed and if it's to the right of center then you're overexposed. Depending on where the spike is, make an adjustment in the editor to get the spike in the exact center. Remember that offset. Now shoot the gray frame again with that adjustment programmed in the meter. Take another shot. Go back to your computer and repeat the same process. This time the spike should be centered. If it's not, then fine tune it until the spike is centered and that should be your meter's offset.

[RRitch]

Rob,

Thanks for the process, I will give it a try. Here is a test shot that I did. The combined light metered at f9 which is what I set the camera at. When I opened it in CS3 it looked over exposed. The final I reduced by 1/3 stop exposure. The exposure looks correct to me after the adjustment. If that is the case I think the meter is over exposing by 1/3 stop. I will try the procedure that you posted and see if that confirms it before I calibrate the meter.

http://farm4.static.flickr.com/3004/3067621283_91256d7966_o.jpg

[RandyMN]

I use my light meter with an incident attachmnet and don't bother with reflective readings when using multiple flash.

Usually I point the incident from the camera position directly at the subject and get accurate results. If using a primary light I have sometimes just pointed at the source of light because I knew the fill was much lower from having measured that already.

If I get multiple sources lighting the same areas such as large group shots, then I fire them all off and take readings from numerous subject positions and use that reading.

I usually get great results but I've been using that technique since the eighties.

[TMR Design]

Rob,

Thanks for the process, I will give it a try. Here is a test shot that I did. The combined light metered at f9 which is what I set the camera at. When I opened it in CS3 it looked over exposed. The final I reduced by 1/3 stop exposure. The exposure looks correct to me after the adjustment. If that is the case I think the meter is over exposing by 1/3 stop. I will try the procedure that you posted and see if that confirms it before I calibrate the meter.

http://farm4.static.flickr.com/3004/3067621283_91256d7966_o.jpg

Hi RRitch,

I just checked the facial mask histogram on this image and it's perfect. No blown highlights or loss of detail and no shadows driven to black. Perfect.

If, for instance, you had a significant specular highlight on the forehead that was creating a hot spot then you might want to meter for that highlight so as not to blow it out and lose detail. There always has to be a balance between a technically correct exposure and a creative one. How you meter can and will vary based on the number of lights used, number of subjects, size of subject area and a host of other variables. Sometimes you need to average across an area to make sure that the subject(s) closest to a light source are not overexposed and the subject(s) farthest are not underexposed.

You want to use your judgement and your eye and correct as much of the potential lighting and exposure problems when setting up and metering so that the image you capture is the best it can be, saving you time in post production and kicking yourself over what you could have or should have done before taking the shot.

[Wilt]

I just bought a polaris flash meter and 2 interfit 150 lights. I have been playing with them trying to get the metering correct. I am using one of the 150s with a 24" softbox as the main and the 2nd 150 with a white shoot through as the fill. When I just the main, I get f8. The fill light is metering f5.6. When I meter the two together I get f9. My question is should I set the camera for f8 (main reading) or f9 (combined reading)? Thanks in advance.

Ignoring first the question about whether or not your meter is in need of calibration...

Light is like water! If you have one hose that fills the bucket using an f/8 opening on the valve, and you add a second source that fills the bucket using an f/5.6 opening on its valve, the final value for two lights (hoses) falling onto that scene (bucket) is indeed going to be a SMALLER opening than f/8!

[NZDoug]

Set your ratios by setting each light individually by metering it.
Then do an "All together now".
Use that setting.
Go click.

[RRitch]

Now that that image and open it on your computer in a RAW editor. It's very important that your RAW editor not have preset adjustments applied. For instance, ACR and Lightroom have some default brightness and contrast settings that alter the histogram upon import. You don't want this to happen. So once you've determined that your editor has been 'neutralized' then look at the histogram. An 18% middle gray frame will show a center spike in the histogram.


Rob,

Can you explain how to "neutralize" ACR. I am not sure how to do this. I think that you mean to adjust the recovery, black, brightness, and contrast settings, but what would I set them to to be neutral?

[TMR Design]

Rob,

Can you explain how to "neutralize" ACR. I am not sure how to do this. I think that you mean to adjust the recovery, black, brightness, and contrast settings, but what would I set them to to be neutral?

I believe that there is a preference in ACR to open files without applying any 'auto' settings. If that's not the case then you want to 'zero' out any exposure, brightness, contrast, clarity, saturation, etc that may be applied. I don't know all the parameters and don't know if they go to 0 or another number to make them neutral but that is the idea.

If you grab a copy of PhaseOne's Capture One software you don't have to worry about any neutralizing. I believe you can download a trial version.

[RRitch]

Rob,

Thanks again for taking the time to answer my questions. ACR 4.x with CS3 no longer applies any auto settings by default. Also there is a 30 day eval of Capture One as well. I need to so some holiday portraits so I am going to calibrate my meter this evening. BTW since I have two different bodies, do I need to calibrate the meter for each one. I will do the test to confirm with both bodies, but hopefully I can use the same calibration for both so I can use both bodies during a shoot without having to calibrate for each one.

[TMR Design]

Rob,

Thanks again for taking the time to answer my questions. ACR 4.x with CS3 no longer applies any auto settings by default. Also there is a 30 day eval of Capture One as well. I need to so some holiday portraits so I am going to calibrate my meter this evening. BTW since I have two different bodies, do I need to calibrate the meter for each one. I will do the test to confirm with both bodies, but hopefully I can use the same calibration for both so I can use both bodies during a shoot without having to calibrate for each one.

It's worth checking both bodies if they are different models. If they're 2 of the same body then don't bother. Hopefully they'll be the same or very close but sensors can vary.

[harroz]

Befor you go playing around with your meter you need to realize something...... if you shoot with one light at f8 does everything look ok? what happens when you have 2 lights together is you have light crossover, this is where light from one light adds to the light of the other, which in effect adds more light, hence why you are getting a different seeting in the middle. it is probably not your meter that is out, it is just that you are getting this crossover. Be aware of this as you'll get all sorts of messed up settings once you change your meter.

Crossover isn't a bad thing, it's just a matter of knowing that this is what happens when you are adding more light

[TMR Design]

Befor you go playing around with your meter you need to realize something...... if you shoot with one light at f8 does everything look ok? what happens when you have 2 lights together is you have light crossover, this is where light from one light adds to the light of the other, which in effect adds more light, hence why you are getting a different seeting in the middle. it is probably not your meter that is out, it is just that you are getting this crossover. Be aware of this as you'll get all sorts of messed up settings once you change your meter.

Crossover isn't a bad thing, it's just a matter of knowing that this is what happens when you are adding more light

Regardless of 1,2,3 or 10 lights. If the meter sees f/8 and it's not calibrated to your camera then f/8 on the meter means nothing. This has nothing to do with number of lights or direction. It's about quantity of light that falls on the dome of the meter.

[harroz]

All I'm saying is test it with 1 light first, it might be that the meter is correct.

I can set 2 lights side by side, 1 light at f5.6, another at 5.6, and have a reading of f8 in the middle. because of this.....


It's about quantity of light that falls on the dome of the meter.

[TMR Design]

All I'm saying is test it with 1 light first, it might be that the meter is correct.

I can set 2 lights side by side, 1 light at f5.6, another at 5.6, and have a reading of f8 in the middle. because of this.....

The procedure I outlined has you calibrate with one light with no more than about 1/10 stop variation across the gray card.

I don't understand why you're even discussing numbers of lights or their relative positions. That has absolutely nothing to do with calibrating your meter to your camera. You're just confusing the issue by mentioning it.

If you're shooting a gray card that is 18% gray then the spike in the histogram should be centered. Once that is correct then all light you meter is correctly calibrated to your camera. Nothing else to think about.

[harroz]

This is why. This was the original post. I'm not saying you are incorrect, jeez!. What you have wriiten is excellent. I'm only explaining why he is getting the jump to f9 thats all. anyway, enough, sorry for trying to help.

When I just the main, I get f8. The fill light is metering f5.6. When I meter the two together I get f9. My question is should I set the camera for f8 (main reading) or f9 (combined reading)? Thanks in advance.

[RRitch]

I understood what Rob was saying about calibrate with a single light and 18% grey card. When I did my test, I metered the main at f8, the fill at f5.6 and combined at f9. When I took the shot I had the camera a f9.

[RRitch]

Ok so I calibrated my flash meter and did some test shots. Here is one of them. Does the exposure look correct? I used a speedlight for the background. It was not powerful enough to blow out the entire background so I did that in post

Main f:/8
Fill f:/5.6
Combined f:/9

ISO 100
1/250
f:/9

http://farm4.static.flickr.com/3025/3081421020_667133f14a_o.jpg

[TMR Design]

Ok so I calibrated my flash meter and did some test shots. Here is one of them. Does the exposure look correct? I used a speedlight for the background. It was not powerful enough to blow out the entire background so I did that in post

Main f:/8
Fill f:/5.6
Combined f:/9

ISO 100
1/250
f:/9

http://farm4.static.flickr.com/3025/3081421020_667133f14a_o.jpg

I took a look at the image in Photoshop. Overall, the image is slightly underexposed. The shirt and arms are receiving a bit more light than the face. The facial mask histogram shows underexposure. It's close, but the skin tones are not being rendered as nicely as they would if you opened up about 1/3 or 1/2 stop.

[bobbyz]

Look at what Robert is saying. He is looking at the image in PS and going by the numbers (histogram and/or RGB values). That is the key. Lot of times people say, "it looks overexposed on my monitor" and then you will hear "your monitor needs calibration". That is not right way to judge exposure. Do it like Robert is doing.

[Papa Carlo]

I took a look at the image in Photoshop. Overall, the image is slightly underexposed. The shirt and arms are receiving a bit more light than the face. The facial mask histogram shows underexposure. It's close, but the skin tones are not being rendered as nicely as they would if you opened up about 1/3 or 1/2 stop.
I must disagree here. See those highlighted areas under the right eye and above brows. They still look ok but on the brink of being blown out. 1/2 more stop definitely would blow them out. The exposure looks perfect to me but I have a reservation about the overall approach. I understand this is just a test but in real life world you do not take shots like that on a white background. A white background is more suitable for children and young females. Shoot this on the black and you'll see the difference.

[Wilt]

I took a look at the image in Photoshop. Overall, the image is slightly underexposed. The shirt and arms are receiving a bit more light than the face. The facial mask histogram shows underexposure. It's close, but the skin tones are not being rendered as nicely as they would if you opened up about 1/3 or 1/2 stop.

but Robert, the shot was made in sunny VA where they tan, not among the pallor filled train stations of Longuyland! ;)

[TMR Design]

Disagreement is fine, and I understand about the tan but in my opinion the overall exposure on the face is a bit underexposed. I could rather have exposed for the whole face and let that small specular highlight blow a bit or used a dot to control the hot spot.

Preference is wonderful thing but for my taste I would like to see more punch in the skin tones.

[RRitch]

but Robert, the shot was made in sunny VA where they tan, not among the pallor filled train stations of Longuyland! ;)


I am on the darker complexion side, plus I have not lost all of my tan from the summer.


I understand this is just a test but in real life world you do not take shots like that on a white background. A white background is more suitable for children and young females. Shoot this on the black and you'll see the difference.

I agree that black would have looked better, but I don't have a black background yet. I tried to convert it to black in post, but it left a white halo and I did not have time to work on cleaning it up. I am hopefully getting a new background for Christmas that is a medium grey with pattern. Then I can use gels to change it to multiple different colors.

[RRitch]

Here it is with a different background. It could be better, but I am at work on my laptop and without the original file.

http://farm4.static.flickr.com/3223/3082817678_94e7b9dbaa_o.jpg

[Wilt]

Disagreement is fine, and I understand about the tan but in my opinion the overall exposure on the face is a bit underexposed. I could rather have exposed for the whole face and let that small specular highlight blow a bit or used a dot to control the hot spot.

Preference is wonderful thing but for my taste I would like to see more punch in the skin tones.

Robert, the first time I looked at the photo and then read your 'underexposure' assessment, I thought the shot looked fine. Without assessing the histogram the way you did, I brought the JPG in and used Paint Shop Pro's automatic adjustment feature, to see what it would do. I know that once in a while I look at a shot and think that it is acceptable, and then Paint Shop Pro does its auto adjustment thing and it manages to improve the shot nevertheless. So I wanted to see it try its magic on this shot....guess what...it did not significantly alter brightness, only marginally did it alter things. So that, too, made me wonder about the 'underexposure' assessment. As for the highlight, if his face had hint of perspiration or facial sheen, I could agree. But I just don't see other supporting evidence of that. If I look at his fingernails, they seem to have about the right amount of sheen that you would expect, and they have about the right level of brightness in that sheen. His left ear exhibits a touch of shine, and again about the level of brightness one would expect. So his facial highlights just don't seem to be too subdued, relative to those other things in the photo. For once, we are not in agreement...I guess marriage is out of the picture! ;)

[TMR Design]

I bumped up the exposure a little more than 1/3 stop. The specular highlights are still present and neither spot (above or below the eye) are blown out or lost detail. To my eye, with the correct exposure the image and skin tones are more pleasing. If the specular highlights are not pleasing then those should have been corrected in the lighting and shooting process, but since there is no loss of detail and no highlights being driven into clipping I don't see why you wouldn't want a better exposed image. I still see a tan and bronzing of the skin but in the edited image I see (and measure) correct exposure.

[TMR Design]

I guess marriage is out of the picture! ;)

Shoot... and I had begun making arrangements for a beautiful wedding ;)

[TMR Design]

Robert, the first time I looked at the photo and then read your 'underexposure' assessment, I thought the shot looked fine. Without assessing the histogram the way you did, I brought the JPG in and used Paint Shop Pro's automatic adjustment feature, to see what it would do. I know that once in a while I look at a shot and think that it is acceptable, and then Paint Shop Pro does its auto adjustment thing and it manages to improve the shot nevertheless. So I wanted to see it try its magic on this shot....guess what...it did not significantly alter brightness, only marginally did it alter things. So that, too, made me wonder about the 'underexposure' assessment. As for the highlight, if his face had hint of perspiration or facial sheen, I could agree. But I just don't see other supporting evidence of that. If I look at his fingernails, they seem to have about the right amount of sheen that you would expect, and they have about the right level of brightness in that sheen. His left ear exhibits a touch of shine, and again about the level of brightness one would expect. So his facial highlights just don't seem to be too subdued, relative to those other things in the photo. For once, we are not in agreement...I guess marriage is out of the picture! ;)

I never use Auto Levels Wilt. It rarely 'knows' what to do.

[Wilt]

Shoot... and I had begun making arrangements for a beautiful wedding ;)


I went back and tried my hand at manual adjustments simply to brightness and contrast, very modest increases to both...I have to admit that I do prefer the photo in the adjusted version, and viewed side by side I have to agree with you after all! Will you take me back??? ;)

Original...then altered:
http://i69.photobucket.com/albums/i63/wiltonw/3081421020_667133f14a_o.jpghttp://i69.photobucket.com/albums/i63/wiltonw/3081421020_667133f14a_p.jpg

Not sure what accounts for the apparent drop in quality resulting from the alteration!

[TMR Design]

Will you take me back??? ;)

Of course Wilt :D