Underexposure or not?

[Pekka]

Andrei wrote:
Pekka, did you see the "underexposure" problem in your D30 ?
Hi Andrei and congrats for your new D30!!!

Sometimes my D30 felt ok and sometimes I was sure it underexposed, sometimes it overexposed a bit.
I did the Q-14 test and it showed that I had 3/4 stop underexposure at most. I did the test a couple of times and the result was a bit different in different lighting. I took it to Canon and there was this extremely nice guy (specialized in digital repairs) who took the camera in. He said they will put it to specs.
A couple of days I got it back and he said some shutter speeds were "off", now he had calibrated the timings. Apparently this is what caused varying results with the test, shutter speeds towards slow were a bit too fast.

Now I have not done the test again yet, as my 70-200 f/2.8L is a repair, too (the bayonett was a bit loose when inserted to the camera, they said it's not normal and they'll replace it, but it takes some time as they have to order the part from germany or Japan) and I'd like to to do the test in exactly similar conditions. But even without the test I can say that the camera exposes better and more evenly accross shutter speeds.

The flash underexposure is a different matter. I have studied the ETTL flash usage with one and two 550EX's. D30 does not try to use flash power in order to balance the histogram. It tries to balance the shadows in the scene. This looks natural, as you see it, but if you want the histogram to go all the way up and more snap you'll need to do about +1 stop flash compensation, sometimes even more. And using FEL: where you lock it is essential and very accurate. If you FEL to a shadow you can get more flash power, if you FEL to highlight you'll underexpose the flash power. With a little practice you can use FEL to tell D30 what direction you need it to go. There is a Canon service document about flash usage, which was posted as images into dpreview by andrzej, and I OCR'd it to text - I'll put it into a separate post.

One of the most important things when evaluation flash exposure is to check from the flash if could achieve what it felt was right: on 550EX you'll see a green light if the exposure was successfull, and often when bouncing it can't get enough light onto subject and the green light does not lit. This shows as underexposure on histogram and photo. So keep an eye of the green light and you'll know if the flash did ok or not.

[Andrei]

Hi, Pekka !

I just can confirm EVERYTHING, you've said:

1. There is underexposure. In my case it's 2/3. I did a test with Kadak grey (I think, I was not understood in photo store, when I asked them about Q-14. O, my English :) )

2. There is underexposure with flash. In most cases it's +1. But if the background is too light - +1/3 - +2/3

New equipment means new problems. But the colors and operations !!! They are just perfect.

[LaptopPop]

Different shutter speeds yielding different results? *DARN*!!!!!

So now, to be thourough, I need to test a full range of shutter speeds....... oh well. At least:
1) it sounds like Canon can fix it if I find anything
and
2) thanks to the glory of digital photography - it doesn't cost me very much at all besides my time.

-lee-

[DanS]

Ok, yes I detect some underexposure. What the Q-14 test?

[Andrei]

1. Obtain a Kodak Q-14 Color Separation Guide and Gray Scale (CAT 152 7662) from your photo dealer.

2. Set up the Gray Scale indoors in typical overhead room lighting and mount your D30 on a tripod. Position the camera roughly 5 feet from the target and parallel to it. Zoom the lens to fill the frame from left to right. Aim the central focusing point at zone 8 on the Gray Scale. Make sure the subject is focused, then shut off the AF.

3. Set the D30 to Manual mode with Partial metering. (DO NOT use an automatic exposure mode.) Other camera settings will be manually selected center focusing point, auto white balance, single frame advance or self-timer, IS0 100, and any JPEG setting you like.

4. Set an aperture of f/8 and, while looking through the viewfinder, adjust the shutter speed until the exposure level indicator lines up in the middle of the exposure level scale.

5. Take a series of non-flash exposures at, over and under the D30's recommended exposure level, using shutter speed as your adjustment. (Note: the camera defaults to 1/2 stop settings, but you can change this to 1/3 stops if you like by means of C.Fn. 4.

6. Examine the resulting images in Photoshop, using the Info palette set for Grayscale (K) values. The K reading for Zone 8 should be at about 65%. Check your images and see which image matches this figure most closely.

Let me know what you find out and we'll take it from there.

Best Regards,

Chuck Westfall
Manager/Technical Information Dept.
Camera Division/Canon U.S.A., Inc.


DanS wrote:
Ok, yes I detect some underexposure. What the Q-14 test?

[Andrei]

This is simple alternative for Q-14

Not necessarily. A gray card is a very useful tool, but it can cause incorrect meter readings when it is used improperly.

If you're really interested in making an accurate exposure test with a gray card as opposed to a gray scale, here are a few pointers:

1. Use the D30's partial metering pattern. This will yield an unbiased meter reading, with no possibility of automatic exposure compensation that can sometimes take place whe the camera is set for evaluative metering.

2. Make sure that the predominant light source is either above or behind the camera position. DO NOT shoot towards the light.

3. Angle the gray card such that it is getting even lighting, but avoid the possibility of bright reflections. These might occur if you angled the card directly towards the sun.

4. Make sure that the gray card fills the partial metering circle shown in the viewfinder, but do not fill the entire picture area with it. This will give you the chance to see how the exposure is affecting other elements in the scene.

5. For testing purposes, shoot at, under and over the camera's recommended exposure level. The D30's AEB function is very useful for this purpose.

6. To minimize lens variables such as evenness of illumination from the center to the corners of the image, shoot at a mid-range aperture like f/8 and vary your exposure with shutter speeds.

Hope this helps!

Best Regards,

Chuck Westfall
Assistant Director/Technical Information Dept.
Camera Division/Canon U.S.A., Inc.


DanS wrote:
Ok, yes I detect some underexposure. What the Q-14 test?

[DanS]

Ok, I'm not sure I did the test right.

I set up an 18% grey card at about 4.5 ft. Camera was focused on an 18% grey card so that the partial metering zone was at the center of the card and the card was in focus. At f/8, I shot -1, 0, and +1.

Imported the files into Photoshop Elements, went to greyscale mode, and took readings with the info palette. I did this three times to ensure accurate readings.

Results: -1 = 85%; 0 = 71%; +1 = 53%

If 18% corresponds to Zone 8 and the reading should show 65%, then this would indicate an underexposure of 6 percentage points. Correct?

Who can help?

[DanS]

My post from DPReview:

"Send it back. It's a very common problem with this camera."


While the 2/3 to 1 stop underexposure IS common, it is NOT a problem. It is by Canon design! Now to explain.

I had a discussion with a Canon tech on this issue. Here is his response.

"Digital cameras need to be exposed more or less like slide film, in that you need to zealously protect your highlight detail: Once you've hit the limit of what the sensor can handle, the image "clips" and all detail is lost in the highlight areas. The thing is that it's quite common for critical highlights to occupy only a very small percentage of the overall image area. Because they correspond to such a small percentage of the total image pixels, the peak at 100% brightness can be very hard to distinguish in the histogram display. To handle such situations, the D30 blinks any pixels that are 100% white on its screen, alternating them between black and white. This makes localized overexposure problems leap out at you, making it very easy to control the critical highlight exposure precisely."

Remember, the D30 is a professional camera. It is NOT a consumer unit. It was designed for those who want to capture the greatest dynamic range in digital--i.e. perfectionists. This can only be achieved by minimizing any "clipping" in the bright areas of an image, and thus maintaining detail in those areas. Consequently, one can use auto exposure bracketing (AEB) together with various Photoshop manipulations to bring out detail in the darker shadows, and thus create the consumate "blended" image. I believe this was the objective of Ansel Adams and some of his techniques--i.e., produce an image with a broad dynamic range and detail throughout--much like the human eye perceives.

To view some "blended-exposure images", take a look at some of Max Lyon's work. http://users.erols.com/maxlyons/

[Pekka]

You know, my D30 underexposed for 3/4 stop, I got it calibrated and now it produces perfect exposure and I can rely on metering. Pro's or anyone else for that matter don't need this 1 stop "built-in" underexposure junk. Very seldom you have EV at 0, you adjust it all the time. If the metering is -1 by default, the EV adjustment logic is altered. Then you buy your next camera and there you have to unlearn your habit of compensating for false metering.

Whne shooting with high ISO, underexposure is a big no-no, you have to get the histogram "full" in order to hide the noise.

And one more thing: clipping is not a problem if you know what clips and why: on a human face it's not desirable, but in bright clouds or high reflections and lamps it's perfectly ok. Clipping is not just "something that went over", it's pure white color, which actually exists in the world in many occasions.

PS. does anyone know any good second hand computer (portable) or camera shops (lenses) in London?

[DanS]

Yes, your logic makes sense as well. I just hate to think about shipping the camera to Canon and being without it!

[redbutt]

Andrei wrote:
1. There is underexposure


Well...that explains a lot about the shots I just took (none turned out worth a damn, but is sure is fun to learn now that I don't have to deal with the film). I went to a concert last night and had a hell of a time getting any decent shots. Granted, my lens is not really made for shooting in a dimly lit bar, but I noticed that when I let the camera do its own thing, it always came out dark...I finally played with the bracketing and found that 1/2 stop took care of the problem.

But, that brings up another question...ISO. I was using ISO 400. D30 says it works from 100-1600, though I am skeptical about 1600. What are the "real" ISO ratings that you can actually use?

P.S. I only have one lens...a Tamron 28-300 LD Aspherical Zoom. It's not anywhere near the caliber of lens that you guys are using, but it is really good for what I need, AND it is nice to not have to change lenses when I want to go from wide angle to zoom.

[DanS]

I recently acquired the 28-70L lens and have begun to run some comparisons with the 28-135 IS. An interesting phenomena occurred which seems to relate to the subject of exposure.

I set the camera on a tripod and took a landscape using Program mode with RAW file format.

28-70: AE set the lens to f/11 & 1/125. No exposure compensation. clik.... Exposure was right on. Removed the lens and mounted the 28-135.

28-135: AE set the lens to f/7.1, but I used the shift-program feature to match f/11. clik.... AF set the shutter speed to 1/200 and the image is clearly underexposed.

Why does the D30 treat exposure differently with each lens?

I converted both RAW images to 8bit TIFFs. I adjusted the exposure on the 28-135 image using PS Elements to match the 28-70 image, then compared the two.

Color is clearly richer and contrast greater with the 28-70 than the 28-135. Consequently, the 28-135 image looks dull by comparison. However, as for sharpness, both seem about equal...when viewed on a computer monitor. Does the human eye treat images with higher levels of contrast as being 'sharper'?

Have others found similar results?

On a side note: I've been using Elements which is limited to 8bit TIFF. I've never loaded the copy of Photoshop LE, which can handle 16bit TIFF, which came with the D30. Would the range of colors appear more robust if I was using the 16bit mode?

Thanks.

[DanS]

Given the findings above, I carried out a little test. I shot the same scene (identical focal distance, f stop and shutter speed) from a tripod to compare these two lenses.

28-70L lens in Program mode

Exposure comp. 0
Parameters: 0,0,0

28-135 IS lens in Program mode

Exposure comp +2/3
Parameters: 1,0,1

FINDINGS: Image contrast, color saturation, and exposure were nearly identical. As one would expect, the 28-70L glass produces a slightly better resolution of the overall image and of course would perform better in lower light conditions, given it's a f/2.8.

But, the 28-135 IS is no slouch when some appropriate adjustments are made. Of course, these adjustments can all be made with PS in post processing if necessary, but it's much easier to start at the highest level the camera is capable of.

Due to less weight, I'll keep the 28-135 for when I'm the all day, sight-seeing tourist, and I'll use the 28-70L for my more serious photographic excursions.

For those on a more limited budget and using only the Canon 28-135 IS zoom, I recommend using some type of color (+1), contrast (+1), and exposure compensation (+1/3 or +2/3) like I've listed above. Your images will no longer seem "dull"....unless you're prone to taking pictures of 'dull' subjects. In that case, use Pekka rule #37465: Find some color! :-)

[reddawn]

Hi

I have both the 28-135 and the 28-70L and I can also say that the D30 tends to underexpose with the 28-135.

Comparing those 2 lenes, with the 50 f1.8 and the Sigma 15-30, the D30 consistently suggest a slghtly underexpose value (-1/3 stop) for the 28-135 at the same focal lenths. I have no idea why ths happens......

sharpess wise, the 28-135 seems almost as sharp as the 28-70 at nearly all focal lengths.....

Red Dawn

[mflaherty]

I also notice an underexposure of between 1/3 and 2/3 of a stop when using the 28-135IS lens. Initially, I thought that I could just leave the compensation setting at +2/3 all the time but found out quickly that, under certain circumstances, +1/3 is better. In any case, underexposure is what's happening with me and that particular lens. Can't comment on other lenses yet. I just bought the 100mm Macro 2.8 but haven't given it a good test yet. I just ordered the 17-35 which is due in this week or early next, and the 100-400IS will be a Christmas gift. I'll be curious to see what exposure issues I discover with these different lenses.

[sasc]

So what is the consensus on this? Mine seems to underexpose too or you could say it exposes for the highlights which I have been used to doing for myself. Is this really a problem to have fixed or not?

[abh555]

Pekka wrote:
...
There is a Canon service document about flash usage, which was posted as images into dpreview by andrzej, and I OCR'd it to text - I'll put it into a separate post.



Did you ever post this? I didn't find it when I searched, but maybe I didn't search correctly?

Thanks!

[mrbobco]

i believe this was from don cohen's site although i can't remember where i found it...but it IS good reading and does answer the question...pretty sure this is whatyou were referring to...

bob

(begin quote)

Letter from Canon on using the D30 with the 550EX and other Canon E-TTL Flashes


(This is a direct quote from a letter sent by Canon to D30 and Speedlite Flash Users)


------------------------------------------------------------------------



Please take the time to read the following letter. It contains a wealth of information on use of the EOS D30 with the Canon Speedlite EX series flashes.

We hope you enjoy your Canon product for many years to come.

The EOS D30 has no sensor to read flash illumination reflected from the CMOS during exposure. If you want auto flash exposure through the lens, you must use one of our EX-series Speedlites. Top of the line right now is the 550EX, and we also offer 420EX, 220EX and Macro Ring Lite MR-14EX. (We had a 380EX that was replaced recently by the 420EX.) For more info on these products including specs, check out our web site at:

canon website/speedlite info (http://www.usa.canon.com/camcambin/cameras/speedlite/550ex.html)

...and go from there. You can combine manual shutter speed and aperture settings with auto flash exposure on the D30 together with any EX-series Speedlite, and you won't have to dial down the flash exposure compensation unless you're trying for a special effect.

* When the lens is set for AF, E-TTL flash exposure is based primarily on the metering zone covering the active focusing point.

* In the case of FEL with the D30, flash exposure is always measured from the center of the picture area, with a metering zone that roughly corresponds to the partial metering circle in the viewfinder.

With these concepts in mind, the next issue is how to determine the active focusing point. The D30 offers 2 basic methods of focusing point selection: manual and automatic.

* When the photographer manually selects an individual focusing point, E-TTL flash exposure remains linked to that point regardless of changes in composition prior to exposure. This is why FEL is so valuable in 'focus lock & recompose' scenarios.

* When the D30 is set for automatic focusing point selection, the camera's algorithm for selection varies according to the user-selected AF mode. When One-Shot AF is combined with automatic focusing point selection, the camera selects the closest readable subject. When AI Servo AF is combined with automatic focusing point selection, the camera expects the photographer to identify the main subject. To do this, the outer focusing points are shut off at first. Once the center focusing point has picked up a subject, the outer focusing points are activated and the D30 is then able to track subject movement from the center to the left or right as well as from near to far or vice versa. When the D30 is set for automatic focusing point selection in One-Shot AF or AI Servo AF, E-TTL flash exposure tracks from point to point along with the AF system.

It's obvious that no single arrangement can work perfectly for every conceivable flash photo, but the range of settings available do cover the vast majority of typical shooting situations.

Here's an analysis of the choices:

1. When you're working with a still subject and there's plenty of time to set up the shot, consider FEL as the best choice because it allows complete freedom in composition under this situation.

2. For point-and-shoot simplicity with stationary subjects, consider E-TTL set for One-Shot AF together with automatic focusing point selection.

3. When you're working with subjects moving laterally across the frame and you are using flash, consider E-TTL combined with automatic focusing point selection. This combination of settings allows the D30 to give you as much assistance as possible in terms of placing maximum metering sensitivity, at the active focusing point.

The choice of One-Shot AF or AI Servo AF with automatic focusing point selection is up to the photographer, but we would suggest trying both to get a feel for how well they work in specific applications.

-----------

Most of the reports we've been hearing from D30 owners indicate that auto flash exposure is very accurate with EX-series Speedlites including the 550EX, 420EX, 380EX, 220EX and MR-14EX as well as the built-in unit.

If you use any of these Speedlites in E-TTL mode, one of the most important considerations is ensuring that the subject you intend to meter is covered by the active focusing point when the flash is metered.

In standard E-TTL flash exposure mode, flash exposure is measured after the shutter button is fully pressed but before the camera's reflex mirror flips up. If you are using autofocus with the D30 and standard E-TTL on the 550EX, you will therefore need to use the Focusing Point Selector to cover your subject with the active focusing point before and during the exposure.

If you have gotten into the habit of locking focus using an individual focusing point, and then recomposing before the shot, you will almost certainly get a bad flash exposure in E-TTL mode with the 550EX or any other EX-series Speedlite. This is because the active focusing point is usually positioned over the background during exposure. There is a workaround, called "Flash Exposure Lock," or FEL for short. This feature allows the camera to memorize the flash meter reading from the D30's spot metering pattern by preflashing the subject using the AE lock button. Once this has been done, then recompose and shoot.

For details on both of these methods (E-TTL and FEL), please refer to your D30 User's Guide, Chapter 4.

You may find that you prefer slightly more or less fill than the 550EX provides at its default settings. If so, adjust the Flash Exposure Compensation setting and take some test shots using the LCD monitor to judge the results. We would also suggest that as a general rule of thumb, you should set the D30's Custom Function 10 to C.Fn. 10-1 at all times. This will put you in complete control of the flash exposure compensation setting and help to make your results more consistent and predictable, especially in outdoor fill-flash situations. Once again, this topic is covered thoroughly in the D30 User's Guide.

E-TTL compares pre-flash information with ambient metering data. It also uses the entire sensor for flash metering. Maximum emphasis is normally placed on the metering zone nearest the active focusing point, but that metering zone is considerably larger than the focusing point alone. It's also possible to get an "averaged" E-TTL flash meter reading by switching the lens to manual focus mode.

(end quote)

hope this helps...

bob

[echoy97]

I have 4 EOS lens, a Tamron 70-200/2.8, sigma 400 APO. All have the underexpose problem with D30 without flash.
I send it to Canon, they tested and claims it is ok according to their "specs", so they didnt fix any problem, send it back to me along with a letter explaining to to use flash with D30.