Flash metering

[wooster]

Hi everyone

I know how to use a flash meter but using my Sekonic 358 with my Fuji XT1 results in slight underexposure compared to my Canons.

My question is this. Should I just use a white towel and find the correct exposure for the whites via histogram? I notice Sekonic recommend using a scene with a range of highlights, mids and shadows but I would have thought the white towel would suffice. Am I wrong?

I will probably manage to set my flash to give the "correct" exposure when I use my usual ISO 200 setting on camera, though I believe this underexposure varies with different ISOs. As a workaround I could measure and remember to compensate when using higher ISOs but does anyone know if it is possible to calibrate the meter differently for the two ISO saved settings on the meter?

[Inkanyezi]

Earlier the standard method was metering off a grey card or with the globe, the latter being the standard Sekonic method. White towels et al are used for calibration, as it is not given that your medium (camera) is calibrated to the same standard as the light meter.

A white towel may be an aid in placing highlights, but just how white you want it in the image is up to personal judgement. It is just natural that your cameras differ a bit regarding which ISO number to use. If you find your shots less bright with one camera, a lower ISO setting on the light meter makes sense. Maybe ISO 200 is spot on with one of your Canon cameras, but you might need to set the meter to 125 or 160 with the Fuji, to get similar results. This is quite normal. You always will have to tune your equipment to perform as you wish it to perform.

[wooster]

Thank you. I guess it's usual for cameras to be different - even between cameras of the same model.

I wasn't very clear in my question so apologies. I'm really wondering if using the white towel technique to calibrate the flash is the best way. I would like to calibrate it so that it is suited to the fuji rather than having to adjust exposure every time. Also does anyone know if I can calibrate the meter differently for each ISO setting?

Thanks again.

[Geoff F]

I use Canon cameras and Speedlite flash so this might not be relevant to you. However, when using flash for macro shots I do a custom white balance (greycard) when I start and redo it if there is a substantial change in the ambient lighting.

The flash output compensation gets manually adjusted for each shot depending on the actual subject and background. Without that I would frequently get over/under exposure problems.

I use the same basic method for all other flash photography. Set the camera with manual settings to suit the scene (aperture, shutter speed and Iso) and use a little flash exposure compensation for every shot.

Also, I always shoot Raw which makes correction of any white balance errors a little bit easier to correct.

[Manfred M]

I also use the L-358, so I find both the question and some of the text a touch confusing. The meter is device independent and will give you a reading, that should be identical, regardless of which camera you are using. It is primarily used as an incident light meter, but accessories like the Lumigrid or spot metering attachments let you also use it as a reflective meter.

So far as I know, the L-358 is calibrated at the factory and the calibration cannot be changed. The higher end L-758 series can be.

Are you using it as a flash meter / incident light meter or as a reflective light meter? If you are using it as an incident meter (something I do 99% of the time), the whole question of white towels and gray cards makes no sense, as you are measuring the light level falling on the subject. You say you know how to use the meter, could you please clarify how you use it. That would help me understand the issue a bit more.

On the surface, it seems to me that the issue is with the two camera's and their ISO settings (i.e. even though the ISO is stated to be the same, it isn't in reality.

[wooster]

Hi again. Sorry for any confusion. I use it as a flashmeter in the usual way i.e. by firing the flash while holding the meter at the subject pointing to the camera position with the globe extended. I understand that cameras expose differently but I wanted to set the meter to allow for this without me having to set different values on my camera from what the meter reading was. in other words I wanted to set my meter to so that the reading gives a correct exposure on my Fuji.

Manfred you are correct that the ISO on the Fuji is quite different from the Canon. This has been documented widely on the internet and is a pain in the rear but I want to overcome it if possible. The other difficulty is that the difference is not equal across all ISOs eg at ISO 200 it is negligible but at ISO 6400 it is over a stop.

To help make it clear, I've downloaded a manual and the relevant section is on p26 5.1 which is headed "Calibration Compensation". I have also been able to find a page on Sekonic's site which gives some more clarity. Here is a link

http://www.sekonic.com/support/faqs/...ash-meter.aspx

Following this search, I probably have all the information I need now. I will use the white towel and place exposure so that the towel has a tonal value of around 245 in PS. This will give me accurate information about how to adjust the calibration.

Other than that all I need to know is whether I can calibrate it differently for two different ISO settings- i.e. those set under ISO1 and ISO 2 buttons. ( so that it might overexpose by say 0.3 stop at ISO 200 and by 1.3 stops at ISO 1600 to overcome the problem I mentioned in my second paragraph about variations in ISO difference) and I will experiment tonight to find that out too.

Thanks

[Manfred M]

I use it as a flashmeter in the usual way i.e. by firing the flash while holding the meter at the subject pointing to the camera position with the globe extended.

You have just identified part of the problem. You are dealing with an incident light meter, i.e. the light that is falling onto the subject. When you are pointing it at the camera, you are measuring something, but it is certainly not the incident light hitting the subject.

The correct way is to be at your subject and point it at the light source(s) you are using; that way you are measuring the light hitting the subject. If you are setting up multiple lights, do each light individually this way, each time pointing the lumisphere directly at the light source.

You might want to watch this video from Frank Doorhof. He is an internationally known fashion photographer, and see how he handles the flash metering. The method he uses is identical to what I was taught at a college level studio lighting course. I first came across Frank through some of the training videos he made for KelbyOne.

https://www.youtube.com/watch?v=f3CTJJ2uVyg

Try that to see if it makes a difference. You are not the first one who measures light that way and I have no idea where that technique comes from, but it doesn't work and gives strange exposures. Also, please note this is why the Sekonic calibration instructions suggest mounting the meter on a light stand and not moving anything, otherwise you will get incorrect readings as the lighting level hitting the meter will change.

[wooster]

Oops. I have an awful feeling that a can of worms is about to be opened. I have seen a lot of heartbreak on forums over this

I disagree with the idea of pointing a flash meter at the light source except in a few specific circumstances. In virtually every case you are indeed measuring light that is hitting the subject as seen from the camera position - which is all that matters to the exposure. The other way is not the way a flash meter has been historically used and is most definitely not the way recommended by Sekonic. They will tell you if you write to them. I know Frank recommends it and so do a few others but it is most assuredly not the traditional way of metering. It causes more confusion and debate on forums than just about any other lighting related issue so I will just respectfully disagree with, I hope, no rancour

[xpatUSA]

Hi everyone

I know how to use a flash meter but using my Sekonic 358 with my Fuji XT1 results in slight underexposure compared to my Canons.

By coincidence, William, I was reading DPR's review of the X-T1 this very morning and this thread triggered a gray cell or two. DPR said:

" . . . although it's also important to understand that Fujifilm's extremely conservative sensitivity ratings mean that ISO6400 on the X-T1 is closer to ISO4000 on most other cameras. . . ."

Source: http://www.dpreview.com/reviews/fujifilm-x-t1/13

Frankly, I find their statement quite odd - because the ISO 2006 Standard defines a 'latitude' range of 5657 to 7127 when a camera is set to ISO 6400 and 4000 is well outside of that range . . . about 2/3 EV below 6400 !!

Could explain your problem, though . . .

Slight rant: sometimes, when reading the 2008 Standard, I wonder if all that verbiage couldn't be simply replaced by:

"The ISO index number is whatever the manufacturer wants it to be"

. . . I will probably manage to set my flash to give the "correct" exposure when I use my usual ISO 200 setting on camera, though I believe this underexposure varies with different ISOs. As a workaround I could measure and remember to compensate when using higher ISOs . .

If you were to swallow DPR's statement, it does give you a sorta ratio for manual compensation at higher ISO settings.

[Manfred M]

. I know Frank recommends it and so do a few others but it is most assuredly not the traditional way of metering. It causes more confusion and debate on forums than just about any other lighting related issue so I will just respectfully disagree with, I hope, no rancour

Of course no rancour.

Please explain to me then how you would set up rim light using the method you propose; say I want it at the same intensity of the key light. In both cases the light will be from behind the subject and outside of the 180° measuring angle of the Lumidome if it is pointed at the camera. The only light that I could measure that way would be the light bouncing around the studio.

[Inkanyezi]

Of course no rancour.

Please explain to me then how you would set up rim light using the method you propose; say I want it at the same intensity of the key light. In both cases the light will be from behind the subject and outside of the 180° measuring angle of the Lumidome if it is pointed at the camera. The only light that I could measure that way would be the light bouncing around the studio.

I'll bite, even if it isn't much help to anyone - assuming that the OP is a bit unfamiliar with incident light metering.

When measuring ratios of light sources from different directions, I always used the flat disc, not the dome, but frankly i never even tried measuring the rim light, as there isn't much point. However it is helpful when measuring fill vs key.

In most cases, the dome is just pointed from the subject position toward the camera, and it takes care of light that hits the subject from all directions except those behind. It is however important not to shade the meter in any way when taking the reading, so a stand for the meter is a great help to get consistent results.

But as xpatUSA just pointed out; the ISO setting is a bit random, so it is no surprise if two cameras won't match. It is quite normal. So the Fuji might give similar exposure as the Canon if the meter reading is taken for a lower ISO setting - i.e. for example 125 when shooting at 200.

[wooster]

Of course no rancour.

Please explain to me then how you would set up rim light using the method you propose; say I want it at the same intensity of the key light. In both cases the light will be from behind the subject and outside of the 180° measuring angle of the Lumidome if it is pointed at the camera. The only light that I could measure that way would be the light bouncing around the studio.

I mentioned rancour because I am pretty new to this forum and have seen this discussion get out of hand, not because I thought you were hostile in any way

If I understand you correctly you are describing measuring ratios which of course needs to be done by pointing the meter at the source. For exposure though the light falling on the subject from the camera's point of view is what we need to know. If we had a situation such as you describe we can assume that the person's face or their hair then I would place the meter where the light was falling onto the subject but still point it at the camera. If I pointed it at the source then the part where it fell onto the subject would be in range of correct exposure but I suspect the face would not be. The globe, when pointed at the camera and place where the important part of the subject is will give correct exposure because it incorporates all the light falling on the subject visible to the camera. Any light not visible to the camera will be irrelevant to the exposure.

If I'm out in the sunshine and take an incident reading I don't point the meter at the sun wherever it is, because I'd end up with underexposure of the subject. Surely the principle is the same?

Having said all that and as I originally said above the point at the camera is pretty much the way I'd for for 95% of metering situations. Obviously there might be extreme examples where you're going for a specific look where you wouldn't. But that's the general approach I'd use.

If I'm allowed to I could link to a lengthy and TBH fairly tedious and impolite discussion on another forum which rehearses all the arguments fairly well. ( I stayed out of it because it wasn't pretty ) I'm not sure if it's against forum rules or not. Can someone let me know please?

[PhotomanJohn]

I have read articles discussing the apparent exposure errors with Fuji cameras. In one article the individual compared the results using multiple RAW converters and found that with some there was no apparent difference in the exposure with the Fuji cameras. He concluded that results when using Adobe Lightroom / ACR consistently appeared under exposed which was not the case with others. There may be something to this.

The method used for metering flash exposure needs to change slightly depending on the situation. Metering with the dome out and pointed at the camera averages the light hitting the subject from multiple sources and yields a good measurement in average lighting conditions. In more extreme lighting conditions this single measurement is not adequate. Accent lights, like hair lights, need to be measured and adjusted separately to provide the desired affect based on the overall exposure used. Measuring the output of an individual flash is generally done with the dome in (or flat) and pointed pointed at the light source. Having the dome in shields the meters sensor from light coming from sources providing a better measurement of the individual light source it is pointed at.

If one bases the exposure on a measurement of the main light source by pointing the meter at that source, the exposure will not be correct for areas of the subject that are illuminated by other light sources in addition to the main light. This is where point the meter at the camera with the dome out will give you a measurement that includes the contribution of all the lights.

[wooster]

I have read articles discussing the apparent exposure errors with Fuji cameras. In one article the individual compared the results using multiple RAW converters and found that with some there was no apparent difference in the exposure with the Fuji cameras. He concluded that results when using Adobe Lightroom / ACR consistently appeared under exposed which was not the case with others. There may be something to this.
.

I wonder if this might be something to do with the DR settings on Fuji cameras. This setting interferes with exposure then adjusts in-camera for highlight preservation. Some RAW convertors take account of this setting and adjust the image as the camera would whereas some don't. Maybe he was using DR function for some shots?

[Inkanyezi]

I wonder if this might be something to do with the DR settings on Fuji cameras. This setting interferes with exposure then adjusts in-camera for highlight preservation. Some RAW convertors take account of this setting and adjust the image as the camera would whereas some don't. Maybe he was using DR function for some shots?

This becomes a bit confusing here. I don't know if the camera would really do such a thing when in M (manual - mode), which is what you set it to when shooting with studio flash and using the flash meter to measure the light. There are several different approaches by camera manufacturers for coping with higher dynamic range when using automatic modes, but when setting the exposure manually, I would not expect the camera to change anything, unless there is some "auto-ISO" feature turned on by the user. (Nikon's approach to Auto-ISO really is confusing).

If there is such a feature, I would expect it to be extensively covered in the handbook for the camera, as it would do something which otherwise is totally unexpected.

[wooster]

This becomes a bit confusing here. I don't know if the camera would really do such a thing when in M (manual - mode), which is what you set it to when shooting with studio flash and using the flash meter to measure the light. There are several different approaches by camera manufacturers for coping with higher dynamic range when using automatic modes, but when setting the exposure manually, I would not expect the camera to change anything, unless there is some "auto-ISO" feature turned on by the user. (Nikon's approach to Auto-ISO really is confusing).

If there is such a feature, I would expect it to be extensively covered in the handbook for the camera, as it would do something which otherwise is totally unexpected.

Agreed. I was wondering if the reviewers mentioned were not using manual mode as they had found exposure errors and found only with some software that the errors were found. I believe Fuji underexposes the file then pushes in camera. This DR "trick" also messes about with RAW files and only some convertors adjust the exposure to the correct value. I seem to recall that Nikon did something odd with their exposure at one point too. Might be misremembering though.

[wooster]

By coincidence, William, I was reading DPR's review of the X-T1 this very morning and this thread triggered a gray cell or two. DPR said:

" . . . although it's also important to understand that Fujifilm's extremely conservative sensitivity ratings mean that ISO6400 on the X-T1 is closer to ISO4000 on most other cameras. . . ."

Source: http://www.dpreview.com/reviews/fujifilm-x-t1/13

Frankly, I find their statement quite odd - because the ISO 2006 Standard defines a 'latitude' range of 5657 to 7127 when a camera is set to ISO 6400 and 4000 is well outside of that range . . . about 2/3 EV below 6400 !!

Could explain your problem, though . . .

Slight rant: sometimes, when reading the 2008 Standard, I wonder if all that verbiage couldn't be simply replaced by:

"The ISO index number is whatever the manufacturer wants it to be"



If you were to swallow DPR's statement, it does give you a sorta ratio for manual compensation at higher ISO settings.

Sorry Ted. I thought I had replied to you but for some reason I hadn't. Yes I know. My fuji does underexpose a lot compared with my Canons. I had wanted a simple way to over come this so the meter reading would give me a good result. It is quite possible to do and I've more or less sorted it now.

I suspect Fuji might be looking for a marketing advantage which is fine but a bit of a pain when you use common elements with two systems.

[drjuice]

Instead of chasing (and forgetting to pack) a gray card or a towel or something similar. You can get the same effect by pointing your light meter at a chunk of asphalt that's had the oil worn off it. In the States, most roads and/or parking lots will get you going. The first thing I do when I get out of the car is to check out the lighting and go from there. I learned this from a Canadian friend who went up to Churchill to checkout the polar bears about 3-4 months after he passed along the tip. The roads there are gravel so he was somewhat out of luck, but he found that the gravel on the non-snowy roads worked pretty well.

virginia