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Andrew Leigh October 9th, 2004 01:59 AM

Exposure problems
 
Hi,

Hi own a 10D and am getting back into still photography.

I am really having a hard time with exposures. When it does go wrong exposure tend to be under rather than over exposed. I keep my metering selection set to "partial" being of the opinion that where I focus is where I need correct exposure. My Auto Focus point is set to one single point, smack bang in the middle.

While getting back into it I have kept all other settings on default, no bracketing on exposure. AWB stays on. However I generally shoot in Av mode and High JPEG more recently RAW format.

With my old camera's I have needed to compensate for exposure when taking subjects with backlighting. With the 10D it does not work effectively, probably because it is already weighted to the centre.

Most shooting is in daylight conditions in very harsh sunlight.

The lenses being used are the 28 - 105mm II USM and a 75 - 300mm IS USM. I try keep to the F8 sweetspot wherever possible.

Suggestions please.

Cheers
Andrew

Ken Tanaka October 9th, 2004 10:02 AM

Hello Andrew,
The 10D's a great camera, eh? I have one and I know that Jeff and a few others here do, also. I, too, climbed back into still photography during the past year or so after being away for most of 20 years.

I recommend trying evaluative metering mode for most of your shots. I know your rationale for using partial mode, but I've found that evaluative is more effective in general on the 10D. If you find a strong discrepancy between brightness on your main subject vs. your background try center-weighted average mode.

Jeff Donald October 9th, 2004 10:32 AM

Are you using your histogram to check your exposure? The histogram is the most revolutionary advancement in exposure since the built in light meter.

Andrew Leigh October 9th, 2004 11:12 AM

Hi,

Thanks Ken.

No Jeff I am not. Checked the manual but did not fully appreciate the value of this tool. I have just checked some of my pic's and as luck would have it I don't get the classic shapes as depicted in the manual. The shots I have been checking are mainly done with flash so there is a predominant bias of the histogram to the left but is very spikey.

In fact very few of my histograms appear normal, most are extremely spikey, eben for shots that are pretty well exposed. While checking I happened to notice the the "zebra pattern" type tool on the highlights DOH. Amazing what you find when you look.

Could you help / point me in a direction that would allow me to interpret the histogram in more detail?

Jeff do you also shoot using evaluative mode like Ken?

Thanks
Andrew

Ken Tanaka October 9th, 2004 11:44 AM

Aha...the plot thickens. <g>

Are you mostly observing underexposure on flash shots? Do you mostly use the 10D's onboard flash or do you use an external flash? If external, which model?

As you may know the use of a flash invokes a new layer of complexity in exposure control.

As an experiment, try placing the 10D in full auto ("green box") mode. Use whatever flash you've been using and take a few shots. How do they look to your eye and on the histogram?

BTW, Jeff is the real shutter doctor. He teaches digital photography professionally. If you're going to weight advice, put his at 300lbs and mine at 150. <g>

Andrew Leigh October 9th, 2004 12:04 PM

Hi Ken,

I am currently using the onboard flash, woefully inadequate I know. Please see my new thread on selecting a flash would appreciate comments.

On the underexposing I was aware that the flash was taking strain and therefore had realistic expectations.

OK, have done the green box experiment. Things are getting clearer. Tried in green box and Av. The green box one is slightly smoother, probably a result of now using evaluative metering. Tests indicate that although the foreground object may be correctly exposed if the background is a fair distance away it underexposes causing the spikey histogram readings.

It is 20:00 and dark here so am unable to do anything other than flash tests. I am keen to have a go tomorrow in the day.


Cheers
Andrew

Andre De Clercq October 9th, 2004 12:29 PM

Histogram interpretation and even more, histogram optimisation, are not always easy things to work with. In very harsh outside lighting conditions there is not so much to optimise by histogram verification that is not "seen"in spatial viewing. The histogram tool gets its full power, only when one can control the light levels locally in a scene. Digtal cams have a limited DR (lattitude) and you can only try to "save" the grayscale parts which are inportant to you by manual setting or by good knowledge about which metering mode is needed for a specific scene content in auto mode.

Jeff Donald October 9th, 2004 04:06 PM

Andrew, this should get you on your way to understanding histograms.

http://www.dpreview.com/learn/?/Glos...stogram_01.htm

http://www.luminous-landscape.com/tu...stograms.shtml

And this is for advanced understanding of exposure and histogram.

http://www.luminous-landscape.com/tu...se-right.shtml

If you have questions post back. On first reading, some of this may not make much sense. But read it several times and what doesn't make sense, ask about.

Andrew Leigh October 10th, 2004 01:45 AM

Hi,

Thanks Jeff,

In the interum I did some web searching and found the second two articles you posted. Found "Expose Right" particularly interesting and important. Had not seen the first which was also highly informative, thanks once again.

The principle is easy to understand and this morning I have already measurably improved on my exposing (not that type LOL). Of course it's easy when you can run inside and download immediately, armed with the information fresh in ones mind. The trick will come when out in the field. I plan on practicing much at home and possibly will draw up a couple of standard reference charts to keep in the camera bag. i.e. Landscape at F16 1/125 half sky half ground = Histogram X etc etc. This until I get the real hang of it.

Thanks again guys.

Andrew

Steven Digges October 13th, 2004 03:33 PM

Andrew,

The consistency of your under exposures baffles me because the 10D is so good at getting it correct, especially outside in evaluative mode. Forgive me for bringing up something simple but Iím wondering if your monitor is calibrated?

Steve

Andrew Leigh October 14th, 2004 02:14 AM

Hey Steve,

now there's a thought.

It may be .......... but I would not know. I recently checked to see if there was a calibration utility available as part of the screen software, could not find any. I did however find a setting howewer where I could alter the colour temperature of the screen. There were two defaults, one of 9500k the other at 5600k. It has been set at 5600k. There were also two custom setting available.

My video card is a 64 meg GeForce 4200i dual head card, it too has some settings I noticed.

Can you get me started on how to calibrate? Is it complicated? Do I need special kit?

The one thing I do know is that monitors do get "tired" over a period of time. I think my monitor is about 6 or 7 years old. It may well be time for a new monitor in any case, but I suppose it too will need calibration.

Perhaps I should start a new thread for this. I find LCD type monitors impossible to use as they constantly give a different result based on the the angle of view. Are CRT monitors still the best for photography / viseography type work?



Cheers
Andrew

Ken Tanaka October 14th, 2004 11:39 AM

Andrew,
While your monitor may not be completely faithful, the fact that your complaint is principally with exposure suggests that it's not the main issue. We judge exposure (by eye) mainly through luminance relationships within the image. For example, areas that have become bleached nearly white or appear less saturated than we remember them from the scene.

Setting the color temperature of your monitor is a color adjustment that affects everything you see in an image (and on your monitor). But an overexposed image displayed at a 5600 deg. K white balance will also look overexposed in a 9500 deg.K white balance.

So while I certainly do suggest that you adjust your monitor's display to be as faithful as possible, the chances are that your images really are overexposed.

There are several tools available to accurately calibrate a monitor but none that are free. All such worthwhile tools require the use of a colorimeter (generally included with a kit) to accurately measure the monitor's display. I use a Monaco system on my Mac.

Steven Digges October 20th, 2004 05:56 PM

Ken,
As you mentioned an overexposed image will always look overexposed regardless of how it is viewed. Detail that is not there, never will be be there. I interpreted Andrews exposure problems to be an almost consistent underexposure. The 10D metering system works too well for this happen under normal daylight conditions, with or without fill flash. If there is a consistent problem, I saw it as possibly one of two things. One, the camera is malfunctioning (I doubted that) or I wondered about the viewing method. An image that is properly exposed can have the appearance of underexposure, especially to an untrained eye if viewed on a dark monitor. Thank you for pointing out I misled Andrew by using the word calibration. I was actually suggesting he start by checking the brightness and contrast levels on his monitor. I tend to begin troubleshooting things in as simple a way as possible and then move forward from there.

Andrew,
How is it going? Are the images consistently underexposed? Have you printed them to see if the prints look bad also? Using Kenís suggestion of trying the green box mode you said that only made a small improvement. Using that mode removed any of your own settings from the process, an excellent way to troubleshoot average conditions. Can you post a picture some place so we can see it?

Your monitor question Ė todays best LCD monitors are ďalmostĒ non-directional. I have 2 20Ē Dellís on my system, I would never go back to CRT.

Andrew Leigh October 22nd, 2004 02:51 AM

Hi Steve,

have shifted to evaluative metering and this has made a difference.

Secondly I have this mental block of using greater than ISO 100, this means in low light I am buggered. I am trying to overcome this and have gone to 400 on occasions. When looking back at the issue most the problems it would now appear were in low light conditions. So, shooting with a 75 - 300mm @ F5.6 in low light, set to ISO 100 with the on camera flash I simply was expecting too much.

Now that I have the 550EX exposure problems appear to be less of an issue.

By the way could you forward me the model numbers of your Dell's as I am currently in the market for a monitor.

Cheers
Andrew

Steven Digges October 26th, 2004 11:09 PM

Andrew,

I run two Dell 2001FP monitors. They are outstanding. Sorry it took me so long to get you the model number.

Iím glad the exposure issue is better. Your on camera flash will also create a curved shadow across the bottom portion of the image with most zooms. The 550EX will serve you well. Spend 20 bucks (US) more and get an omni bounce diffuser to snap onto it, you will like the result.

Shoot a bunch of photos under the same conditions at 100, 400, & 800 ISO Ė print them, and take a good look, the results are shocking. Things have changed, digital is better than the large grain of the old emulsions.

Steve


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