Inconsistency in flash metering

[o hey tyler]

I completely disagree with this. I shoot with flash at 800 and 1600 all the time.

OP, I have a feeling your flash is working too hard. ISO800 at f/5.6 in that environment? Way too dark. Do you have a faster lens? ISO 800 is fine, but not at 5.6. I even often shot at 1600 and 2.8 to really brighten the background. That is why it takes your flash forever to recycle. You probably needed a new battery pretty quick.

I also shoot with flash on a higher ISO. Better carry, and it doesn't work the flash so hard.

 

[Robin_Usagani]

Usagani Photography | Our own wedding photography nightmare

Yes.. the photographer used low ASA. It sucked.

ISO 800 with flash seems excessive also.. I usually shoot flash at 100, seldom more than 400.

I completely disagree with this. I shoot with flash at 800 and 1600 all the time.

OP, I have a feeling your flash is working too hard. ISO800 at f/5.6 in that environment? Way too dark. Do you have a faster lens? ISO 800 is fine, but not at 5.6. I even often shot at 1600 and 2.8 to really brighten the background. That is why it takes your flash forever to recycle. You probably needed a new battery pretty quick.

So we have different styles of shooting... so what? We already knew that! I prefer lower ISO... that not make it wrong. Keep in mind that when I was learning to shoot, 1600 didn't exist yet.. and when it did finally roll around, it had a lot more grain than 100 did (almost to the point of being unusable, IMO). So I am used to shooting at lower ISO's... and prefer them.

You are still new to photography, Robin... you have picked it up fast, and you do nice work. But don't be telling some of the older crowd that we are wrong, and you are right... that would be rude!

 

[cgipson1]

Yea.. and it was not that long ago, was it? And not long ago you didn't know enough to pick a good photographer ( you said that yourself in a previous post)! And that individuals bad photography was because they didn't know how to use that low ISO, or their camera, or flash, etc.. and probably had low end gear to begin with.

So now you are blaming poor wedding photography on the photographers choice of ISO? lol! That doesn't make any sense.. and you know it!

Usagani Photography | Our own wedding photography nightmare

Yes.. the photographer used low ASA. It sucked.

I completely disagree with this. I shoot with flash at 800 and 1600 all the time.

OP, I have a feeling your flash is working too hard. ISO800 at f/5.6 in that environment? Way too dark. Do you have a faster lens? ISO 800 is fine, but not at 5.6. I even often shot at 1600 and 2.8 to really brighten the background. That is why it takes your flash forever to recycle. You probably needed a new battery pretty quick.

So we have different styles of shooting... so what? We already knew that! I prefer lower ISO... that not make it wrong. Keep in mind that when I was learning to shoot, 1600 didn't exist yet.. and when it did finally roll around, it had a lot more grain than 100 did (almost to the point of being unusable, IMO). So I am used to shooting at lower ISO's... and prefer them.

You are still new to photography, Robin... you have picked it up fast, and you do nice work. But don't be telling some of the older crowd that we are wrong, and you are right... that would be rude!

 

[Robin_Usagani]

Charlie, I simply disagreed with you. The OP is photographing an event. Your method will make the whole background dark. Why would you want to shoot an event like that? Maybe if you are in a small room it is fine, not in a big room.

 

[cgipson1]

Charlie, I simply disagreed with you. The OP is photographing an event. Your method will make the whole background dark. Why would you want to shoot an event like that? Maybe if you are in a small room it is fine, not in a big room.

I have lit up entire churches, and got good shots with ISO 100 film and a single flash (of course it was a T-45 flash, that helped! lol!)... it is more how you use it, Robin. Never had a problem with dark backgrounds either... and don't have problems with recycle times, or overheating either (that is what battery packs are good for!) Dragging the shutter works just as well at low ISO as it does high ISO if you know how to use it.

 

[Robin_Usagani]

Here you go.. at least for Canon system, it is NOT affected by camera metering mode.
Flash Photography with Canon EOS Cameras - Part I.

 

[Vtec44]

I have nothing to contribute to the discussion because I don't know much about Canon's. I had a discussion with Robin yesterday on Facebook and we both agreed that he needs to switch to Nikon. hahahaha...

 

[TCampbell]

The 2nd (darker) image is a bit unusual since Charlie's EXIF viewer says you used center-weighted metering (Don't do that when using flash. You're fighting the E-TTL II system and not letting it do it's job.)

The reflected metering system on a camera wants to assume a "middle gray" (used to be 18% but now it's almost always 12% gray). When you point it at a dark point, it wants to assume it should be capable of being "middle" gray and probably just needs more light. So it'll fire more light to attempt to compensate. This has the undesirable consequence over over-exposing the things that really were middle gray and blowing out things that were high tones.

I grabbed my 5D II body (I usually shoot a 5D III these days, but I still have and occasionally use the 5D II), one of my 600EX-RTs, set the camera to ISO800, f/5.6 and 1/60th (to mimic your settings) and did some test shots playing with the metering modes against both white backgrounds and black backgrounds.

As expected, if I switched to spot mode and allowed the center point to be on a black background, all the non-black things in the foreground were over-exposed. In evaluative mode it was correctly exposed.

The 5D II will use "E-TTL II" mode (more advanced that E-TTL) with that flash. E-TTL II will read focus distance information from the lens (assuming your lens supports it, but most lenses do.) HOWEVER... distance info can ONLY be used if the flash is (a) on the camera and (b) not being bounced (pointed straight at the subject.) Generally you want to bounce or feather the flash whenever possible -- or even get it off the camera or use it in conjunction with external lights (e.g. a side-light). The problem with this is that while the camera may "know" how far the focus distance is from lens to subject, it does NOT know how far away your external lights are, nor does it know how high up your ceiling is when bouncing. That means it can't use distance info (and it knows how to detect this and wont even try) when any of those situations are true. As soon as you tilt the flash head to any position other than straight-ahead, the distance measuring data is no longer used. NOW it's going by how much of a difference it reads at with two different metering measurements. It pre-meters the scene (using no flash). Fires the pre-flash while simultaneously metering the scene again. It compares the difference between the non-flash and pre-flash metering instances to see how much of a difference the pre-flash made. It then uses that info to decide how much power to use when the shutter is open. Since you used spot metering, it was not allowed to take into account anything about your subjects (and they're basically the only thing you cared about getting exposed correctly.) That's what I meant when I said you're not letting the E-TTL II system do it's job.

What really surprises me about that 2nd image is that I would have predicted that with your settings that not only would you not get a correct exposure, you should have had an over-exposed shot (and I'm really surprised you didn't. I cannot re-create your result with my camera and flash and I'm using the same camera, flash, and settings that Charlie says you are using.) This makes me wonder if you haven't dialed in some flash exposure compensation and didn't realize it (the EXIF data doesn't include that info, but then it also doesn't include the lens info either and usually it does. Your image only contains partial EXIF data. The camera would have included that data when it saved the image.)

Check your Flash Exposure Compensation... on the 5D II, the third button (from the left) on the top (in front of the top LCD) is the ISO/flash± button. Press that, then the rear dial can increase or decrease flash exposure compensation. You typically want this at "0" for normal flash power when indoors and using a single light. I decrease this usually to about -1 when shooting outdoor in daytime and using the flash as fill.

In summary...

1. get out of spot-metering mode and go back to evaluative.
2. check your flash exposure compensation and make sure you didn't inadvertently change that.

I use spot-metering in concert venues, but I'm specifically targeting that center point on my subjects face to meter their skin when I use that mode. If you use spot metering, make sure you are taking the meter reading off of something reasonably close to a middle-gray value. It doesn't have to be perfect (you've got lost of adjustment latitude in post production as long as it was reasonably close. Especially avoid black or white.)

 

[Robin_Usagani]

Tim, show me a documentation that the TTL flash metering is sampling from the same area as your camera metering. I have a black canon battery charger in the middle of a white wall. I set my cam to manual, spot meter the charger and shot it with ETTL flash. Then I shot it with center weight average. Both shots are identical. I have not seen anywhere on the manual or websearch that says the flash reading is taken from the same area as the camera metering.

 

[Robin_Usagani]

After a long ass research and testing, I am 100% sure that canon speedlite does evaluative metering as factory setting(not affected by the camera metering mode). Since the OP is a Canon user.. I take this as I am right

Charlie, you kinda contradicted yourself though. The middle box you drew is all dark. Theoretically the photo should be bright and not the other way around.

 

[TCampbell]

Robin, remember it's a "TTL" metering system. There are lots of variants but what they all have in common is "Through The Lens" -- aka "TTL".

The flash doesn't meter, only the camera does. Back in the days of thyristor flash units, the flash did the the "metering" (well... not true metering. The system looked for a specific amount of return light and then cut off the flash when it received enough light. It was easily fooled.) But in modern TTL systems, there's always some form of a pre-flash which the camera "meters" followed by another flash at some power level calculated by the camera based on the results of the pre-flash.

Each evolution of TTL systems tries to make them a little more clever and a little harder to fool.

I have NOT seen any official documentation from Canon that goes through all the rules. I have seen a lot of books, magazine articles, blogs, etc. which go over several nuances. I encountered one article that indicated that only certain bodies would allow overriding the metering system when the flash is in use, but it was the "pro" bodies (specifically the 1D and 5D series bodies) that seemed to have the ability to do this. That is to say... an entry level body might use evaluative metering when the flash is in use regardless of what metering system you set on the camera... but a pro body would actually use the metering system you selected (even if it was not a good choice.) I probably would not be able to find that same article and I don't specifically recall the list of bodies (only recalling that the bodies listed were high-end bodies.)



Keep in mind, I don't think any of us have claimed to be sure we're right about why the OP got poor results from that 2nd image. His result seemed to be the opposite of what I would have predicted. But since I have the same camera body and the same flash, I set everything up using the same settings as the OP to see if I could recreate the problem -- but could not. All that really tells me is that we haven't hit upon the correct reason to explain WHY the OP is having this issue (Not that there isn't an issue... clearly there is. He posted sample photos to show us.)

We're all just trying to helpful here by evaluating what could possibly account for his results. Please lets try to avoid jumping to conclusions. From a rational approach (e.g. think "scientific method") -- unless we can consistently re-create the OPs results, then we can't be sure why he got those results. That's what I was hoping to do by testing with my 5D II & 600EX-RT combo (but so far have not succeeded.)

Something else to consider, Robin, is that if you point the flash straight ahead, then the E-TTL II system will also use the distance calculation to determine how much flash to fire. If you tilt the flash away (e.g. bounced or feather) then the camera doesn't know how far your bounced surface is -- it can't use the camera guide number and inverse square laws to calculate a pretty accurate power level. This might explain why in your specific case you were unable to see a difference.

We don't know if the OP used the flash straight-on, bounced, or feathered the lighting. He mentioned he takes some straight-on, some feathered, and some using a Fong diffuser. When I look at the first photo (the one with adequate lighting), the lighting does not appear to be bounced or feathered light. I'm going to "guess" that this shot was taken with the flash straight-ahead. That would have provided distance information to the E-TTL II system. The darker photo has highlight & shadow that suggests it is like a "bounced" photo using the Fong diffuser -- and if that's true then the camera wouldn't have been able to rely on distance information to set flash power. Now it's much more heavily reliant on the reflectivity of the surfaces.

 

[Robin_Usagani]

Tim, the argument is the sample area of the flash metering.. Is it the same as the camera metering? I am aware what TTL is. Pretty obvious why the 2nd one is darker, it has more reflective surface.

 

[Josh66]

Some (most?) flashes do have a meter though...

Here's a question... I have some cheap-as-hell Cowboy Studio radio triggers (and they work great, provided that the batteries aren't dead ... not one issue in maybe 5 years...). Does the transmitter send camera settings to the receiver, or just a signal to fire?
Also - same question for a PC cord - do camera settings get sent too, or just a "fire" command?

I didn't think cheap-ass triggers like that would do anything but send a "fire" signal (it only has one contact on it). Anyway, I can put my flash (580EX II) on E-TTL mode, off camera, using these triggers - and it works. Direct or bounced, it somehow figures out the right exposure, apparently without knowing what ISO I'm using, or the aperture.

Now, there is a custom function on the 580EX II that will allow you to manually input the ISO and f-stop - but I'm not using that.


I honestly cannot explain why it works, but it does - every time. Everything that I know about how this stuff works should say that it shouldn't work at all. I mean, I know that the flash has it's own meter - but what good will that do if it doesn't know the ISO & aperture that the camera is set to? Hell, it even works on film cameras that the manual outright says that the E-TTL functions of the flash are not compatible with.

 

[TCampbell]

Tim, the argument is the sample area of the flash metering.. Is it the same as the camera metering? I am aware what TTL is. Pretty obvious why the 2nd one is darker, it has more reflective surface.

Does it have to be an argument? Can't it be a discussion?

It's possible we're agreeing but using different terminology. I thought I saw you refer to the flash metering and was attempting to convey that the camera always does the metering when using any of the TTL variants. The flash may impose restrictions on what metering modes can be used by the camera when the TTL flash is in use.

His EXIF data indicated that he used "spot" metering. That leaves open the possibility that the flash allows spot metering on a 5D II ... or that the EXIF data reports the mode set by the camera menu even if the flash imposed a different mode.

Over the weekend I may do some further experiments to see if I can't find a way to reproduce the OP's results. I've thought of a few things that I haven't tried yet.

 

[Robin_Usagani]

Tim, if you go to external speedlite menu on your camera, you only have 2 options.. evaluative and average. You can have your camera be on spot metering but your flash will only be on evaluative or average. So for canon, it does not matter what metering mode is on your camera, the ETTL flash reading will still be the same.