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Archive 2013 · Flash Exposure Compensation v/s Manual mode ?
  
 
mjoshi
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p.1 #1 · p.1 #1 · Flash Exposure Compensation v/s Manual mode ?


Okay for all flash gurus here, I'm experimenting and learning more of OCF. So how do you figure out what is correct power for flash when you put flash in Manul mode. Is there any basic rule/guide for it or you simply do a test shot see on viewfinder how it looks and then set Falsh power accordingly ?

Sorry for not mentioning what I'm using It is 580Exii + 430Exii + Canon 5Dmkii. To start with and keep things simple I'm experimenting only with 580EXii off camera with 5Dmkii, Once I've figured things out I'll add 430EXii in mix.

Edited on Feb 09, 2013 at 01:16 AM · View previous versions



Feb 08, 2013 at 08:43 PM
Mark_L
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p.1 #2 · p.1 #2 · Flash Exposure Compensation v/s Manual mode ?


Use a meter or the histogram. Whether it is one or the other usually results in a flamewar

I find TTL worthless off camera, you end up using compensation anyway and then end up with each shot being slightly differently exposed depending on framing. Just as quick to use manual and then you have consistent exposures.



Feb 08, 2013 at 09:08 PM
RustyBug
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p.1 #3 · p.1 #3 · Flash Exposure Compensation v/s Manual mode ?


The "basic rule" (read "old school") for manual flash is to know the GN of the flash (for a given ISO) and calculate the relationship between the aperture being used and flash to subject distance.

For instance, if your flash has a GN of 80 feet (for a given ISO), and it is placed 10 feet from your subject, the aperture should be at f8. Flash power (GN), aperture & flash-to- subject distance are inter-related.

Manually calculating the aperture, flash-to-subject distance, flash power ratio based on GN vs. chimping your viewfinder, reading your histogram or using a flash meter ... all are viable strategies that you'll find your comfort / preference for using.

Personally, I like knowing my GN for a baseline ... but once you start using zoom heads, or bouncing off walls,ceilings, reflectors, softboxes, etc. it gets a bit trickier to keep track of how they alter the effective GN. Some people live & die by chimping the viewfinder, without having a clue @ what a GN or light meter even are. Others live & die by the meter.

Definitely more than one way to skin this cat ... whatever works for you, or what you happen to have at your disposal at the time. Typically, I've usually (not always ) got my brain along with the histo & LCD with me. And for those times I've left my brain behind, I grab my meter.



Feb 08, 2013 at 09:41 PM
hdthomsen
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p.1 #4 · p.1 #4 · Flash Exposure Compensation v/s Manual mode ?


I'm also interested and looking for some pointers on manual flash. I had read Bryan Peterson's book on understanding flash which I found really helpful and thought I was ready to go out with my new SB700 and start figuring/calculating my flash to subject distance etc., but it turns out the method he describes doesn't actually work in practice (at least with my flash) when off camera. So I'm looking for a good explanation (whether by book, blog post or whatever anyone can describe here) to have a better understanding of how to set flash manually.

I learned exposure in manual and almost always do that and want to have similar control over flash exposures, but my mind is getting tied up in knots trying to actually reason out I should set the flash at. Your description of using the GN was a good start Rusty, so I'm looking for something along those lines....just more of it with examples etc. Thanks all.



Feb 08, 2013 at 09:57 PM
alohadave
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p.1 #5 · p.1 #5 · Flash Exposure Compensation v/s Manual mode ?


I use flashes that have a calculator on the back. Most Sunpak models have sliders that allow you to dial in your distance, ISO, and aperture, and you adjust the power to match.

Then you tweak it from there.



Feb 08, 2013 at 09:58 PM
alohadave
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p.1 #6 · p.1 #6 · Flash Exposure Compensation v/s Manual mode ?


hdthomsen wrote:
I'm also interested and looking for some pointers on manual flash. I had read Bryan Peterson's book on understanding flash which I found really helpful and thought I was ready to go out with my new SB700 and start figuring/calculating my flash to subject distance etc., but it turns out the method he describes doesn't actually work in practice (at least with my flash) when off camera. So I'm looking for a good explanation (whether by book, blog post or whatever anyone can describe here) to have a better understanding of how to set flash manually.

I learned exposure in manual
...Show more

http://strobist.blogspot.com/2006/03/lighting-101.html
http://strobist.blogspot.com/2007/06/lighting-102-introduction.html

Read through, and do all the exercises in both links.



Feb 08, 2013 at 10:00 PM
Graystar
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p.1 #7 · p.1 #7 · Flash Exposure Compensation v/s Manual mode ?


mjoshi wrote:
Okay for all flash gurus here, I'm experimenting and learning more of OCF. So how do you figure out what is correct power for flash when you put flash in Manul mode. Is there any basic rule/guide for it or you simply do a test shot see on viewfinder how it looks and then set Falsh power accordingly ?


You didn't say what camera and flash. There are differences between Canon and Nikon flash systems.

Nikon's TTL flash meter is pretty good. But if I have time, I'll use a gray card to set my flash exposure.

For setting ambient light exposure, I'm able to spot meter my white-balance reference (which is about 30% gray or so) and then set 1.3 EV of Exposure Compensation (a value arrived at through a simple "calibration" process.) If I spot meter my WB card and set 1.3 EC, I get correct exposure. If I then take a picture of the card, the card registers as a spike right on the first line from the right side of the histogram. I can use this information to set exposure for flash.

I'll set up the key flash, put the WB card at the subject position, facing the flash, and in A mode I'll set the Flash Value Lock. The camera comes up with a flash exposure and locks it in. Now I take a picture of the WB card and check the location of the spike in the histogram. It usually only takes one EC correction to put the spike on that first line from the right side of the histogram. I take a second shot to confirm, and I'm ready to shoot.

The advantage of using FV Lock is that I can now change aperture at will, and the camera will adjust the flash power to provide the same exact exposure. I can put the camera in manual mode and increase the shutter speed into the High Speed Sync shutter range, and the flash exposure will remain locked and consistent. This provides quite a range of control over aperture and over the ambient light...from almost full ambient exposure to completely suppressed...without having to mess with flash exposure. Once FV Lock is locked there's nothing more to do other than tweak it with EC if I feel the need. It's a pretty quick setup as well. Just set the lights, hold the WB card at the subject position, take a picture of it, and review. Once you're used to the process you can set an exact exposure level in half a minute.

Note, however, that I'm talking about Nikon. With Nikon I can use Exposure Compensation to adjust the flash. You can't do that with Canon. Why does that matter? If you're using several wireless lights in two or three groups, using EC will adjust all of them at the same time. After EC has been adjusted for the Key light, you can then go into the Flash Commander and adjust individual groups, relative to the current exposure, with positive or negative FEC. This lets you set a key at one level, a fill at -1 FEC, another fill at -2 FEC, and adjust all three up or down with the camera's EC, without changing the relative relationship between the flash units.

This methodology requires more knowledge and understanding than the typical GN method or (more often) the trial & error method of all manual flash. It requires understanding your cameras functions. In that regard, it could be said that it's not "easier" than manual flash. But I don't care about "easy"...I care about function. Once set (a process which is quick to do) the control over the shooting parameters is unmatched in speed and ease. There's simply no way to adjust aperture or control ambient light as quickly and as consistently with all-manual flash as you can using FV Lock.



Feb 08, 2013 at 10:25 PM
Steve Wylie
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p.1 #8 · p.1 #8 · Flash Exposure Compensation v/s Manual mode ?


Or you can use a good light meter....


Feb 08, 2013 at 10:40 PM
ukphotographer
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p.1 #9 · p.1 #9 · Flash Exposure Compensation v/s Manual mode ?


Mark_L wrote:
Use a meter or the histogram. Whether it is one or the other usually results in a flamewar

I find TTL worthless off camera, you end up using compensation anyway and then end up with each shot being slightly differently exposed depending on framing. Just as quick to use manual and then you have consistent exposures.


Consistent flash exposure, yes.

The OP asked about Manual flash.. and EC so OK, TTL is not really the topic, and I would probably suggest what you do.. but I have a question.

Just putting this out there...

What do you do when you're shooting outside, the sun is coming in and out from behind clouds, your ambient exposure is shifting between f5.6 to f16 and the client needs a bright continuous background to emulate summer with the subject lit like a summer's day - and its still winter... and you have about 15 minutes to shoot after setting up?

Graystar's suggestion would probably work OK - except that with EC the background would change too (and shifting into FP mode shutter speeds would lead to a wild flash underexposure). It would probably be OK if you have a camera capable of FEC and EC separately, but how would you manage just using Manual?



Feb 08, 2013 at 10:45 PM
basehorhonda
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p.1 #10 · p.1 #10 · Flash Exposure Compensation v/s Manual mode ?


Steve beat me to it, but honestly hes right. The use of a light meter really will help you out. I spent a few years doing the ol shoot and chimp until I got it how I wanted it on the back of my camera. It worked for me and I got a bunch of good looking shots, but to streamline my photoshoots, the addition of a light meter 3 months ago made me wonder why it took me this long to get one.

The other thing is just experience. Getting to know your equipment and how it works will do wonders for you.



Feb 08, 2013 at 11:25 PM
 

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Graystar
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p.1 #11 · p.1 #11 · Flash Exposure Compensation v/s Manual mode ?


ukphotographer wrote:
What do you do when you're shooting outside, the sun is coming in and out from behind clouds, your ambient exposure is shifting between f5.6 to f16 and the client needs a bright continuous background to emulate summer with the subject lit like a summer's day - and its still winter... and you have about 15 minutes to shoot after setting up?

Graystar's suggestion would probably work OK - except that with EC the background would change too (and shifting into FP mode shutter speeds would lead to a wild flash underexposure). It would probably be OK if you have a
...Show more

That's an interesting situation that has recently been addressed by Nikon (for auto mode shooting...that is.)

In general, when shooting in changing-light conditions the best way to assure consistent exposure is to base your exposure off of the subject by picking one spot to act as a reference point and applying EC appropriate for the tone. Nikon cameras really shine in this regard, because spot metering follows the selected focus point. You can move your focus point and place it on the same spot on the subject for every shot. Exposure will be based on that one tone, and will be consistent regardless of how the light is changing. This provides consistency while also allowing you to reframe and recompose as you like. (With Canon I believe only the D1 series provides spot metering that follows the selected focus point.)

When you're in such conditions and you want to control flash exposure and ambient exposure separately, the method used depended on the camera. With Canon cameras you would just shoot and adjust your EC and FEC as needed. Canon is one of those cameras, as you suggested, where FEC and EC are separate. Adjusting EC on a Canon doesn't affect the flash exposure. On a Nikon, however, adjusting EC does affect flash exposure, and so you would end up doing the EC/FEC jig. If you want to change your ambient, you would need to apply an opposing amount of FEC to maintain your flash exposure. This is a pain.

Fortunately, Nikon has seen the light and the D4 and D600 have a custom setting to decouple EC from flash exposure (didn't make it into the D800 for some reason.) Hopefully all the new bodies will have this function. So if you find yourself in such a situation, you can decouple EC, and control ambient exposure separately. This allows you to use auto exposure for both flash and ambient. And if you meter the same tone on the subject then you'll have consistent exposure that can be precisely controlled using EC and FEC.



Feb 09, 2013 at 12:42 AM
RustyBug
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p.1 #12 · p.1 #12 · Flash Exposure Compensation v/s Manual mode ?


+1 @ Dave's comment on calculator on the back. Again, kinda "old school", but yet they work pretty well. Some will show a digital display of the "distance range", from which you can pretty much assume that full power equates to max distance.

BTW ... which model flash(es) are you working with?

@ UK's scenario ... aperture priority @ camera to keep subject exposure consistent with manual flash. Metering/EC for BG to adjust shutter to accomodate ambient in/out. Unique scenario, but doable.



Feb 09, 2013 at 12:55 AM
cgardner
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p.1 #13 · p.1 #13 · Flash Exposure Compensation v/s Manual mode ?


In ETTL mode FEC=0 is just camera metering best guess. How scene is composed and content affects results to it is always a process of shoot, evaluate, adjust. If the clipping warning is turned on its easy to see where clipping is happening. Just raise FEC up until the black outs appear in playback then back off one click (1/3 stop).

With manual you make the first guess. And then chimp the same way with the same dial on the back of a Canon flash and wind up at the same power.

Manual is more consistent when subject <> flash distance isn't changing, like portraits. Dial in once and exposure the same frame after frame regardless of what you put in front of camera. In a situation like portraits is subject in dark suit / white shirt takes off jacket no exposure adjustment will be needed.

ETTL is more convenient when moving around shooting at an event like a party but less consistent. In a situation like portraits is subject in dark suit / white shirt takes off jacket meter will usually require an FEC adjustment.

When shooting ETTL with dual flash and A:B ratios, I set ratio first to Master A (fill) 1:2 Slave B (key), then FEC per highlight clipping. Creates a full range of detail in black suit / white shirt.

When shooting portraits with M I use identical flash power and control ratio with distances. Shooting from 8ft with similar OCF at around 6ft creates average "normal" looking 3:1 reflected ratio with full range in black suit / white shirt. Quite simple and foolproof if the same set-up is used session-to-sesson. I set up and am shooting in less than 5 min with 1-2 test shots to confirm exposure.

More details on my tutorial site: http://photo.nova.org



Feb 09, 2013 at 12:59 AM
BrianO
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p.1 #14 · p.1 #14 · Flash Exposure Compensation v/s Manual mode ?


ukphotographer wrote:
...The OP asked about Manual flash.. and EC so OK, TTL is not really the topic...


Since FEC only works with TTL flash, I would say TTL is the topic, at least in part.



Feb 09, 2013 at 04:50 AM
BrianO
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p.1 #15 · p.1 #15 · Flash Exposure Compensation v/s Manual mode ?


mjoshi wrote:
...Is there any basic rule/guide for it or you simply do a test shot see on viewfinder how it looks and then set Falsh power accordingly ? ...To start with and keep things simple I'm experimenting only with 580EXii off camera


The 580EX II has a range indicator on the LCD panel. In ETTL mode it will show the minimum and maximum ranges for the aperture and ISO you have set. In Manual flash mode it will show a single range -- also based on the aperture and ISO set. As you change the power level (or the aperture or ISO setting) the distance will change accordingly.

That's a starting point only, because the subject reflectance, your artistic choice on lighting intensity, etc. may vary from the calculated distance's intensity.

I use a flash meter rather than relying on the range graph, but even then it's still only giving a starting point for the reasons mentioned.



Feb 09, 2013 at 04:56 AM
ukphotographer
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p.1 #16 · p.1 #16 · Flash Exposure Compensation v/s Manual mode ?


BrianO wrote:
Since FEC only works with TTL flash, I would say TTL is the topic, at least in part.


Well.. in the title - anyway.



Feb 09, 2013 at 11:56 AM
Allynb
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p.1 #17 · p.1 #17 · Flash Exposure Compensation v/s Manual mode ?


Seems like an engineering degree is need here...light meters and GN are the easiest and quite accurate too.


Feb 09, 2013 at 08:58 PM
cgardner
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p.1 #18 · p.1 #18 · Flash Exposure Compensation v/s Manual mode ?


Allynb wrote:
Seems like an engineering degree is need here...light meters and GN are the easiest and quite accurate too.


In my experience (40+ years) rated guide numbers are usually overrated by the flash maker. Actual results also vary with environment. Actual GN will be greater in small indoor room than outdoors due to spill. GN also varies with zooming flash heads and is only practical when zoom is fixed by either using a single FL lens like a 50mm or manually zooming. The GN / Distance = Aperture equation also doesn't work when flash is bounced.

Light meters straight out of the box are accurate to ANSI standards for measurement but an f/5.6 meter reading usually will not produce correctly exposed highlights on a white shirt when camera is set at 5.6. That's because there is another variable: ISO My Canon 20D and 50D ISOs are about 1/3 stop different than my L-358. A 5.6 meter reading and aperture blows the white highlights at 5.6. By doing a bracketing test around 5.6 and looking at the detail in the whites I found aperture of 6.3 renders the white highlights correctly. Why? Because the actual ISO of the camera sensor, measured against the same ANSI standard as the meter calibration, is around 120.

Because camera sensor and film is seldom equal to the number on the dial or box a Sekonic L-358 has two different ways to compensate.

Starting with meter off, pressing and holding both ISO A and ISO B buttons while power is turned on will put it in the first mode. The dial on the side is then turned to enter the compensation factor. With my bodies it is .3 stop. After the .3 offset is entered the same power light will read 6.3, what the test indicates is needed.

The second method is identical to the first except it is done with the power on. I prefer to use this one because anytime a calibration adjustment in play a [-/+] icon appears on the meter display as a reminder.

This is a file from one of my meter accuracy test. The meter reading was 5.6 but this file shot at 6.3 was one that looked more like the actual highlight target. There is some glare on the target but for that test only the white towel was the baseline for "nominal" (i.e., accurate highlight detail)

http://super.nova.org/XP/MeterCompTest/MeterCal6_3.jpg

As noted below I always expose in camera to err on the side of underexposure. So your target values on a target like that may differ from mine. Do whatever works for you.

On meters without the compensation factor the same offset can be produced by changing ISO. That's how I did it to calibrate film speed based on shadow detail above base on B&W and color negatives.

It was testing my speedlights and compensating my meter using a white textured terry towel to evaluate loss of highlight detail that I noticed the correlation between when the loss of detail and the playback clipping warning. The areas that black out correspond to the loss of detail on the towel.

There is a bit more headroom in the RAW files than indicated on the camera playback, but like cutting a log to make a 8' long 2x4 it's wise cut the long 8ft. 3in. to allow for finishing. In the case of a RAW file finishing are the steps converting it from a 4500 px wide 16 bit ProPhoto file to a 900px wide 8 bit sRGB file for a web page. If the solid whites are 254 just under clipping in RAW they will often wind up clipped in the small JPG. I see this a lot in files I critique because I open them in Photoshop Levels, hold down alt/op and click the highlight input slider. Try that and you'll see this:

http://super.nova.org/XP/Photoshop/PS_Levels/BlownH.jpg
Colors / color overlays = channels clipping.

Clicking on the shadow slider with alt/opt key pressed reveals areas in file channels which recorded no signal.
http://super.nova.org/XP/Photoshop/PS_Levels/BlownS.jpg

What would be ideal would be for cameras to have warning for both the highlights and the shadows. What I do in nearly every situation with ambient or flash, ETTL or manual is:

Raise exposure until I see clipping start somewhere in the playback
Reduce exposure by 1/3 to make the warning disappear.
Look at the shadows in the playback and the LEFT side of the histogram.

The clipping warning gets the detail recorded in the highlights. Looking at the mid-tones and shadows in the playback image tells me if the scene exceeds sensor. If scene exceeds sensor's range the histogram bars on the far left in the 0-20 range will have very high amplitude, darkest areas will have no detail and mid-tones will be rendered darker than normal / expected if seen by eye in person in that situation.

YMMV but my definition of NOMINAL exposure is a file where there is a full range of detail similar to what would be seen by eye. That will not occur when scene exceeds sensor range unless the photographer:

1) Changes the range of the scene foreground with flash

2) Manipulate the file in Photoshop (middle slider left Levels correction)

3) Bracket and then blends exposures with shadow and highlight detail (HDR)

Overcast lighting and fog are situations where sensor range is longer than the scene producing a histogram like this if exposure is set in the middle off a gray card:

http://super.nova.org/XP/Photoshop/PS_Levels/FogHisto.jpg

In a situation like that the contrast can be "normalized" by moving the left and right sliders in Levels inward and adjusting the middle slider right "to taste".

http://super.nova.org/XP/Photoshop/PS_Levels/LevelsOvercast/OvercastDay.jpg
http://super.nova.org/XP/Photoshop/PS_Levels/LevelsOvercast/OvercastLevels85.jpg

I'm an old dog but I started manipulating contrast with the Zone System, multi-grade B&W print papers and halftone reproduction in the 70s and started using Photoshop in the early 90s on scans years before I every used a digital scanner. That's why my concept of "correct" exposure may differs than yours. I prefer the term "nominal" as defined by a full seen by eye range. That was my goal in B&W zone system shot and still is my goal in every digital file I take. That works for me. Try everything, then decide what works for you and accept it will not work for everyone. I don't.

With digital my exposure workflow starts by exposing the highlights under clipping and for that the clipping warning is like an "idiot" light on a car dash saying a car has overheated or run out of oil. Use it and highlights will never be unintentionally blown. I avoid needing to blow highlights for the sake of "normal" mid-tones because I always have a flash on bracket on my camera for situations where the scene exceeds sensor and a second in my bag as needed.

Here's a typical outdoor flash workflow for me:

http://super.nova.org/XP/Lighting_OutdoorFlash/FlashWorkflow.jpg

1) Expose for the ambient highlight detail below clipping with clipping warning
2) Add flash to "normalize" the foreground using a bracket (natural downward vector modeling)
3) Use adjustment layers in Photoshop to tweek the results (like dodging and burning a print)

With two flashes set in ETTL ratios at 1:2 with Master A - Fill over camera and Slave B off camera I can record a full range of detail in the foreground of a bride and groom standing with sun behind them with no problem. That for me is a "nominal" flash assisted exposure. The background out of range of the flash will not be nominal so I crop it out when framing the shoot if I think the loss of detail will be noticed

When I can't use flash I try to keep the sun at my back and the shadows BEHIND the content of the scene because that keeps the range of the scene closer to the range of the sensor. Then as always I expose for the highlights under clipping.



Feb 09, 2013 at 11:47 PM
ukphotographer
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p.1 #19 · p.1 #19 · Flash Exposure Compensation v/s Manual mode ?


Allynb wrote:
Seems like an engineering degree is need here...


It's worse...

Over 10 ft a 1" change in flash distance can make a 0.1 stop change in exposure. I recommend head clamps.



Feb 10, 2013 at 02:18 AM





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