Underexposed?

I have recently joined the digital domain (Canon EOS 400D) after my 35mm cameras languished too long in the back room. I am so far just experimenting to learn how these things work and excited by the versatility. I am however having a difficult time figuring out whether I have a problem demanding a trip to the repair center or not.

All of the pictures that I take with the flash seem underexposed, even after getting the Speedlight 430EX. If I push the RAW image up one stop, they are much better. The problem also seems evident under low light exposures. However, if I go for the sunny day f16 test it seems right on (1/ISO setting).

Although not too familiar yet with histograms, the underexposure seems evident there too as the histogram is basically totally contained in the bottom half with nothing in the upper half. Should I send this back to the repair center, or deal with it?

Hi Randy,

Please be welcome. On this one before we even worry about bad setting, I need you to do two things.

First, find the manual for both your flash and body and then look up how to set FEC in both.

Secondly, ensure that both the flash and body are set to zero.

I know with the XT and the 550 EX if FEC is set to zero on the flash, then the FEC setting on the body kicks in.

hope this helps,

Sean

Welcome to OPF. We're probably going to need more info, but there are a few obvious things to check. First, what's the subject distance? Is the whole frame underexposed, or is there a central subject that's properly exposed? Regardless of how much power you have you can't light a near subject and a distant background evenly with a single light. What mode are you using? I assume it's similar for the 400D, but on the 20D Av mode defaults to fill flash mode, which might not be what you want. You also need to beware of the max sync speed, so what's your exposure length? If you try to go faster than the sync speed you lose flash power rapidly.

Flash Exposure Compensation is another possibility. If you have that dialed down accidentally it could cause problems. Make sure that's set to zero, or you could even bump it up to see if that helps. Make sure the flash unit is in E-TTL mode.

The Canon flashes these days seem to do a pretty good job in many situations, so this seems like an odd problem.

You might also post an example or two.

Aaron

welcome randy!
i don't have your camera or flash, but i usually have at FEC +2/3 with the 580 on my 5d, and before that on my 10d. so i would suggest to you that if you keep FEC on the + side all the time and if this solves the problem for you then this is not a problem requiring repair.
let us know!

Sean DeMerchant said:

Hi Randy,

Please be welcome. On this one before we even worry about bad setting, I need you to do two things.

First, find the manual for both your flash and body and then look up how to set FEC in both.

Secondly, ensure that both the flash and body are set to zero.

I know with the XT and the 550 EX if FEC is set to zero on the flash, then the FEC setting on the body kicks in.

hope this helps,

Sean

Click to expand...

Thank you for the speedy respose. FEC on both flash and camera are set to zero. FYI the manual says that the 430EX FEC overrides any camera FEC.

Aaron Strasburg said:

Welcome to OPF. We're probably going to need more info, but there are a few obvious things to check. First, what's the subject distance? Is the whole frame underexposed, or is there a central subject that's properly exposed? Regardless of how much power you have you can't light a near subject and a distant background evenly with a single light. What mode are you using? I assume it's similar for the 400D, but on the 20D Av mode defaults to fill flash mode, which might not be what you want. You also need to beware of the max sync speed, so what's your exposure length? If you try to go faster than the sync speed you lose flash power rapidly.

Flash Exposure Compensation is another possibility. If you have that dialed down accidentally it could cause problems. Make sure that's set to zero, or you could even bump it up to see if that helps. Make sure the flash unit is in E-TTL mode.

The Canon flashes these days seem to do a pretty good job in many situations, so this seems like an odd problem.

You might also post an example or two.

Aaron

Click to expand...

Subject distance is 8-10 feet with the wall another 5 feet behind. Exposure mode has either been full auto (green box) or "P". Shots have been synching at 1/60.

How do you post an example? When I try all I get is a script prompt for a URL?

Marian Howell said:

welcome randy!
i don't have your camera or flash, but i usually have at FEC +2/3 with the 580 on my 5d, and before that on my 10d. so i would suggest to you that if you keep FEC on the + side all the time and if this solves the problem for you then this is not a problem requiring repair.
let us know!

Click to expand...

Thank you. While FEC is certainly a potential workaround, I am a bit fussy about things working correctly. Admittedly, I haven't shot a lot with this box yet so am still learning, but it seems to underexpose shots without flash in low light or even regular light. I will try more when we get a cloudy day.

Randy Brand said:

Subject distance is 8-10 feet with the wall another 5 feet behind. Exposure mode has either been full auto (green box) or "P". Shots have been synching at 1/60.

Click to expand...

That distance may be pushing the popup flash, but the bigger flash should certainly be able to handle it. E-TTL II plays some games with the preflash trying to judge the reflectivity of the subject. If the subject is very reflective it may be fooling the camera, but since it sounds like you've tried multiple subjects that should be the problem.

Green or P shouldn't do anything funny and 1/60 wouldn't be the problem. You're not using a really small (numerically large) aperature are you? For flash work that actually matters, as the flash duration is much shorter than the shutter speed. Automatic mode should take care of that unless you're going beyond the capability of the flash at full power.

How do you post an example? When I try all I get is a script prompt for a URL?

Click to expand...

Everyone gets around to this question eventually. OPF doesn't host images, so you must have another place to host them (such as pbase in my signature, lots of options). Your post merely links to them, hence the URL prompt. Search is your friend, as this has been answered many times in great detail.

There seems to be a school of thought that the 400D just inherently underexposes a bit. I find mine to be dead on, but it is a bit conservative, perhaps because it doesn't have a much headroom for blown highlights as some other Canon bodies. I always ran my 1D bodies at +2/3 exposure comp though, and usually run my 1D Mark II's at +1/3. A meter is just relative. Learn how yours works and adjust yourself accordingly. It could be on the wide side of the spec envelope, but it certainly doesn't sound as though it's "defective."

Nill
~~
www.toulme.net

I agree with Nill. My 400D is usually set to +1/3 exp. comp. Re. flash (I use a 580EX), I haven't had problems which were odd/frequent enough to demand special attention yet. Yes, I run into underexposure when using the flash every now and then, but this is mostly due to the fact that I use a diffuser/bouncer and fire the flash at an angle of 45 degrees. This lowers the flash capacity considerably.

Having said that, if you use the flash on the camera with the settings already recommended by the helpful folks here (smile) and you still get a histogram with pixels in the lower half only, then I would assume that something is not right.

Cheers,

Aaron Strasburg said:

You might also post an example or two.

Aaron

Click to expand...

Nill Toulme said:

There seems to be a school of thought that the 400D just inherently underexposes a bit. I find mine to be dead on, but it is a bit conservative, perhaps because it doesn't have a much headroom for blown highlights as some other Canon bodies. I always ran my 1D bodies at +2/3 exposure comp though, and usually run my 1D Mark II's at +1/3. A meter is just relative. Learn how yours works and adjust yourself accordingly. It could be on the wide side of the spec envelope, but it certainly doesn't sound as though it's "defective."

Click to expand...

The 400D has more highlight headroom, relative to metering, than any other Canon DSLR - in the RAW data. For JPEGs, however, it is more wasteful of highlights.

John Sheehy said:

The 400D has more highlight headroom, relative to metering, than any other Canon DSLR - in the RAW data. For JPEGs, however, it is more wasteful of highlights.

Click to expand...

Not sure I understand John. "...more highlight headroom, relative to metering..." suggests exactly what I was saying, i.e., that the 400D meters more conservatively. But I doubt it meters differently for RAW and jpg, so I'm missing the meaning of your statement. Please clarify.

Nill
~~
www.toulme.net

Randy Brand said:

Although not too familiar yet with histograms, the underexposure seems evident there too as the histogram is basically totally contained in the bottom half with nothing in the upper half. Should I send this back to the repair center, or deal with it?

Click to expand...

To test the ambient exposure, set the EC to 0, point at an evenly lit white or grey wall, and look at the histogram. If the camera is metering as designed, the middle of the hump (or the green hump, if the histogram is RGB), should be at about the 45% point on the histogram. Now, turn on the flash, and with the flash and both camera EC settings at 0, take another picture. Now the histogram should be at about the 55 to 60% mark.

If it is wildly off from these, then perhaps metering is defective.

That said, if you shoot RAW, you can set the EC a bit higher for everything, as "normal metering" for JPEGs on the 400D results a very conservative under-exposure of the RAW data. The camera meters for about 1.2x the ISO stated in the camera's settings, but the RAW sensitivity is more like 85% of it; IOW, when the camera says ISO 100, it actually meters for about ISO 120 (as most Canon DSLRs do), but the RAW data responds as if the camera's ISO 100 was really ISO 85 (which it really is).

Nill Toulme said:

Not sure I understand John. "...more highlight headroom, relative to metering..." suggests exactly what I was saying, i.e., that the 400D meters more conservatively. But I doubt it meters differently for RAW and jpg, so I'm missing the meaning of your statement. Please clarify.

Click to expand...

I just replied to the OP, not realizing that this was an older thread. I addressed what your asking somewhat, but I'll address your question more directly here.

If you put a tripod-mount lens on a tripod, and attached both a 400D and a 20D, and used the same manual settings for ISO, Av, and Tv, the RAW data from the 400D will be 1/2 stop weaker (about 72%) than the RAW data from the 20D.

Both cameras, when set to ISO 100, will meter for ISO 120. The 20D RAW data will react like it is ISO 120, with about 3.3 stops of highlight headroom above middle grey. The 400D would have to be metered for ISO 85 or so, to maintain the same standard amount of headroom (it has about 3.8 stops when metered for ISO 120). IOW, *ABOVE AND BEYOND* any "conservative" approach the 400D may or may not have in metering for its JPEGs, it also routinely *wastes* 1/2 stop of highlights, and dynamic range, causing under-exposure in the shadows.

I shoot RAW with my 400D, and the EC range I use is 0 to +2 (and +2 often isn't enough). I use 0 where most people would be using heavy negative EC.

Thank you for the response. Take a look at IMG_078 and the histogram at the flickr site referenced above. That was of gray siding in bright clear sunlight. The histogram displayed on the camera is definitely at about 40 percent of the range. The one posted at flickr seems the same if I am understanding the range displayed in that program (Canon's Digital Photo Professionsl) is broader on the low end than on hte high end.

I will be near Irvine week after next and the repair center said they might be able to check it out while I am in the area. I will post the findings after. I would be surprised that relatively accurate meter operation wasn't part of QC on finshed product, but ya never know..... I suppose many could be cutting corners wherever possible to trim costs.

Hi Randy, and welcome to OPF,

While I understand where you're coming from, I'm afraid that you can't be "a bit fussy about things working correctly" when it comes to metering, whether it be exposure metering or, as in your case, flash metering. This is because the camera has no real idea about what "correct" is.

The only thing that knows how you want to expose your image is you. Your camera is a tool that should be used to produce the image that you want, not the other way round. Using full-auto mode and expecting good results will more often than not lead to disappointment and frustration.

It's very difficult for us to properly analyse your problem from a distance. There are many reasons that the flash exposure may not be correct. Two of the most common are:

1) The subject doesn't have the famous "18%" reflectivity
2) Flash to subject distance is too large

The first point is very important. Just as for classic exposure, the camera assumes that the subject being lit by the flash has an average reflectivity, and exposes for that. If your subject is brighter or darker than average then you'll have to change the FEC to correctly expose the subject.

To understand how to properly use your new flash, you should read this definite article on Canon flash:

http://photonotes.org/articles/eos-flash/

Best regards, and happy reading,

Tim

Ah, good Tim. I was just going to suggest that link. ETTL has long been the subject of misunderstanding and either a love or hate relationship LOL. ETTL II works very nicely if you understand the hows. I also recommend practice and experimentation until one understands using it, how to apply FEC, etc.

Diane

Factory Set Under-Exposure, Voodoo and more...

Flash issues aside, bare in mind that the Rebel DSLR's all under expose by -1/3 to -2/3 stop straight from the factory. This is not done by any DSLR above these models, and I don't know why this is.

Just a guess on my part why Canon does this but it could be that the majority of the market for Rebel DSLR's are newbies, ex P&S shooters, people that most often don't shoot raw, nor want to post processing. For this group of shooters, Canon under exposes on purpose so that images straight out of the camera are more contrasty, more punchy, more saturated, etc. So that the images look like "Sony Candy" that they were use to before, when they shot with P&S's.

As for flash, there is NEVEC...secret voo-doo Canon logic that is undocumented by them, which under exposes the flash on purpose for certain situations....I cannot find the link which explains this in detail yet, but perhaps another poster can.

Hope this helps.
Dan

is this wall behind white by any chance? is your subject wearing white or a light blue? Flash is anything but automatic and will underexpose with a white or light subject and overexpose with a dark or black subject. Takes getting used to so as to learn to predict it.

Thanks to all for your help and advice. I was in Irvine, and dropped the camera off at the service center to have the light meter checked. Interestingly, the receptionist suggested that I leave the lens as well to get the focus checked. They did find the light meter out of adjustment, and it is much closer now. They also found the focus off on the lens and adjusted that. Whatever happened to good quality control?

"What happened to good quality control?"

Manuafacturers make products only "good enough" that few enough people have problems that it costs less to fix the problems than to increase the quality control measures.

Perfection is the enemy of the good - Gustave Flaubert

Edited 3/9 to correct attribution