How do you guys/gals measure under/over exposure?

Please forgive me if I'm asking a beginner's question.

Over the last while I've read many posts, some quite recent, about lenses that miss the exposure. Either going to dark or too light. The poster will sometimes show a photo of a house or a tree or what ever to illustrate their point.

My question is how are these folk so confidently determining that their camera/lens combinations are giving a 1 2/3 stop under exposure or a 2 stop over exposure, or what ever may be the case?

I must be wrong but some times I get the feeling that they are guessing or judging the exposure by what 'looks' good on their screens.

OK, I'm probably not being fare but are these folk really using a valid repeatable provable technique for testing their gear? I've yet to see how they go about determining the exposure variances that they are talking about.

On the whole, I think you are probably right.

In any case, there is no such thing as the "correct" exposure - it's subjective.

Hear2see said:

Please forgive me if I'm asking a beginner's question.

Over the last while I've read many posts, some quite recent, about lenses that miss the exposure. Either going to dark or too light. The poster will sometimes show a photo of a house or a tree or what ever to illustrate their point.

My question is how are these folk so confidently determining that their camera/lens combinations are giving a 1 2/3 stop under exposure or a 2 stop over exposure, or what ever may be the case?

I must be wrong but some times I get the feeling that they are guessing or judging the exposure by what 'looks' good on their screens.

OK, I'm probably not being fare but are these folk really using a valid repeatable provable technique for testing their gear? I've yet to see how they go about determining the exposure variances that they are talking about.

Click to expand...

--
My photos:
http://nickburtonswildlifephotography.blogspot.com/
http://nickburton.smugmug.com/

The histogram tells you if you are over or under exposed.

Archie

Archie said:

The histogram tells you if you are over or under exposed.

Archie

Click to expand...

thank you for your comments...
...from what I've read, the Histogram tells us what the camera captured.

Interpreting the profile of the Histogram is somewhat daunting for me.

The best way to judge if the lens is shooting under or over would be to shoot a known target, say a nice big 18% grey card and then check the Histogram to see where the spike sits on the Histogram.

If the grey card's spike is smack dab in the middle of the Histogram then the lens is bang on. If not centred then we can read more or less, just how much it is off.

Shooting a grey card would demonstrate exactly what their lenses are doing. No?

While the right exposure is really purely subjective, there are some factors that tell with higher confidence if the image is over or under exposed. The first factor - blown highlights (over) or blackened shadows (under). Histogram shows it easily. But some images are too contrast and have both: blown highlights and blackened shadows, so in this case it is neither over nor under exposed image, it is simply overly contrast.

If shooting at night most images will show as underexposed anyway, but our bright mind suggests that exposure is just right

The bottom line - if you shoot with RAW, most (if not all) images are correctable and notion of over-under exposure stops making any sense (unless you miss the exposure by more than 1 stop). Visually you can easily tell if image is over or under exposed if it is off by at least 1/2 stop.

P.S. Many newbies (I was myself) confuse camera or lens incorrect exposure with incorrect metering. If you set single point metering you have great chance to miss correct exposure.

Hear2see said:

Archie said:

The histogram tells you if you are over or under exposed.

Archie

Click to expand...

thank you for your comments...
...from what I've read, the Histogram tells us what the camera captured.

Interpreting the profile of the Histogram is somewhat daunting for me.

The best way to judge if the lens is shooting under or over would be to shoot a known target, say a nice big 18% grey card and then check the Histogram to see where the spike sits on the Histogram.

If the grey card's spike is smack dab in the middle of the Histogram then the lens is bang on. If not centred then we can read more or less, just how much it is off.

Shooting a grey card would demonstrate exactly what their lenses are doing. No?

Click to expand...

How do you know it is the lens and not the camera, or combination?
--
D5000 - Nikkor AF-S DX 18-105mm F/3.5-5.6G ED VR - Nikkor AF-S 50mm f/1.4 G
Canon PowerShot S3

I read a discussion a while back about how 18% grey was not the best measure and 16% was a better point. It was a dull read (probably 2% too dull ?)

I think your eyes looking at the final shot are the best bet. If it looks too dark it is too dark. The camera can do a great job but it is not foolproof. I use the histogram. It's a useful guide. I still tweak things on my p.c. using a cailbrated monitor. My eyes are the final judge.
--
http://www.andrewsandersphotography.co.uk

Hear2see said:

...from what I've read, the Histogram tells us what the camera captured.

Click to expand...

Yes and no, the Histogram shows the brightness distribution of the final processed image - the JPEG. This is important, because the Picture Control settings have a huge impact on the histogram. In the default setting the Picture Controls increase the midtone brightness and this results in overall brighter images, but not exactly in very accurate exposure (if accurate exposure is the goal and not good looking images).
The Histogram doesn't show the brightness values of a raw file (NEF).

Hear2see said:

If the grey card's spike is smack dab in the middle of the Histogram then the lens is bang on. If not centred then we can read more or less, just how much it is off.

Shooting a grey card would demonstrate exactly what their lenses are doing. No?

Click to expand...

Yes and no - again

The histogram will show if the resulting JPEG with all Picture Control settings applied is over or under exposed. Depending on the raw converter used this can be different from the result you can get from a raw converter.

Normal grey cards (18% grey) are to bright to get medium grey, the light meter will be fooled into very slight underexposure. It's often advised to use +0,5 EV to get the right exposure with a grey card (and spot metering).

I use spot metering and a grey card to test the exposure characteristics of my lenses and the internal exposure meter. I compare the results to images where I used the exposure settings I got from my external exposure meter.

Many lenses have corner shadowing and this can influence the exposure or the impression of exposure (image looks darker). Some lenses have lower light transmission, this won't influence the exposure meter of the camera, but it gets problematic with a external exposure meter.

What over- and underexposure is, depends on the photographer/viewer. The whole image could be over- or underexposed or just a part of the image could be over- or underexposed.

Example: an image could be overall overexposed with blown highlight in the sky/background but the main subject (let's say the face of someone) could be under exposed or correctly exposed.

In digital photography, notions of underexposure or overexposure have to do with signal optimization and your intentions for rendering the scene in the end. But exposure is only a part of that process, and just refers to the amount of light hitting the sensor and being recorded. The rest has to do with gain and A-D conversion.

If you shoot film or JPGs, your notions must be limited to the fixed results of the development/conversion process. Under these circumstances, if you want 18% gray, you must calibrate your exposure to end result at the outset.

This is complicated by things like picture controls (in Nikon terminology) that impose stock tone curves, which skew the gradations from dark to light. The most accurate way to evaluate your exposure is using the "neutral" picture control.

When shooting RAW, you may take the additional step in optimizing the signal of "exposing to the right" which means to expose as much as possible without blowing any highlights (that you didn't intend to blow). In this case, you will have to decide how to render the tones you captured. This is of course a wonderfully clean way to put a subject into the shadows -- first by boosting the exposure in camera, and then reducing it in post.

Not so technical maybe but I often just look at the screen for highlight ""blinkies"'if I judge that they are important parts of the shot then I gradually underexpose until they have gone...any underexposed shadows I retrieve in PP. Works for me.

I've often wondered this also.

It seems a lot of people are comparing the exposure of a particular lens with that of another they own that they believe gives correct exposure.

Unless it's by 2-3 stops or something crazy, it seems to be quite a subjective assessment though. I've seen people post images to show that their lens was overexposing while others thought they looked terrific and perfectly exposed

It's always puzzled me how people say a lens is "dark" also - I've heard the 16-85 referred to as dark a few times. Does this mean it underexposes?

Hear2see said:

Please forgive me if I'm asking a beginner's question.

Over the last while I've read many posts, some quite recent, about lenses that miss the exposure. Either going to dark or too light. The poster will sometimes show a photo of a house or a tree or what ever to illustrate their point.

My question is how are these folk so confidently determining that their camera/lens combinations are giving a 1 2/3 stop under exposure or a 2 stop over exposure, or what ever may be the case?

I must be wrong but some times I get the feeling that they are guessing or judging the exposure by what 'looks' good on their screens.

OK, I'm probably not being fare but are these folk really using a valid repeatable provable technique for testing their gear? I've yet to see how they go about determining the exposure variances that they are talking about.

Click to expand...

You really have to undestand your histogram and look at the result and learn how to use exposure compensation to achieve what you want. There are many many tutorials all over the net about using it. It really is a importent tool provided free by the camera. Use it.
--
Brian
http://briandrinkwater.smugmug.com/

I tend to like a saturated image, underexposing slightly to get this affect. It is easier for me to used manual exposure along with the histrogram and adjust the exposure meter needle up or down a half of f stop checking the histrogram after each shot to about where I want the exposure to be.

Larry

Luke Kaven said:

If you shoot film or JPGs, your notions must be limited to the fixed results of the development/conversion process. Under these circumstances, if you want 18% gray, you must calibrate your exposure to end result at the outset.

Click to expand...

Spoken from the mouth of someone who probably has never set foot in a darkroom

Just FYI, film is very tolerant of exposure correction after being developed initially. It still helps to get the exposure right first as you'll retain more detail where you want it (just like digital) but during my short period of shooting B&W film I discovered the joys of correcting horribly exposed shots by adjusting the exposure time of the paper on the enlarger.

Hear2see said:

OK, I'm probably not being fare but are these folk really using a valid repeatable provable technique for testing their gear? I've yet to see how they go about determining the exposure variances that they are talking about.

Click to expand...

I think this is not an easy one. Mostly, folks have an idea where they want the right-hand-side edge of the histogram, and roll the exposure-compensation wheel accordingly until they're happy, when they have time to play. Then, in some time, they mostly know where EC needs to be in the average, and when to adjust it a bit.

For more reliable results, one may shoot a white wall in the M mode and watch the histogram (rhs edge), compare same-exposure combinations (mind that the axis of the histograms is mostly not linear with the exposure), and compare with more trusted lenses. The results may depend on the aperture, zoom and focus positions.

Most ridiculously, the metering may also depend on certain conditions, specifically it seems the meter can be rigged to compensate for lack of light at wide apertures so that the auto-metering experience is better than what open-loop measurements in M mode show.
See some of my efforts here:
http://forums.dpreview.com/forums/readflat.asp?forum=1030&message=35099206

joejack951 said:

Luke Kaven said:

If you shoot film or JPGs, your notions must be limited to the fixed results of the development/conversion process. Under these circumstances, if you want 18% gray, you must calibrate your exposure to end result at the outset.

Click to expand...

Spoken from the mouth of someone who probably has never set foot in a darkroom

Click to expand...

Not for 30 years, but I did all my own darkroom work then.

joejack951 said:

Just FYI, film is very tolerant of exposure correction after being developed initially. It still helps to get the exposure right first as you'll retain more detail where you want it (just like digital) but during my short period of shooting B&W film I discovered the joys of correcting horribly exposed shots by adjusting the exposure time of the paper on the enlarger.

Click to expand...

I wouldn't underexpose BW film more than a half stop. Of course overexposing is standard procedure for many situations. Slide film has a lot of range, but one is best advised to get it right in the camera.

As I said, you must calibrate your exposure to the end result with film. Compare this with shooting on a D7000 where you can pretty much boost the ISO after the fact without significant penalty.

Thanks for the good ideas about exposure and reading the Histogram.

The tips and cautions about being tricked by the Picture Controls and the different Picture Settings like, Neutral versus Vivid was something I hadn't though of, when evaluating the specifics of a lens' performance.

but my question was..

How are posters measuring the under or over exposure of their lenses with such specificity?

...I'm getting the distinct impression that posters may be guessing or giving impressions about their gear... instead of actual measured results.

deang001 said:

I've often wondered this also.

It seems a lot of people are comparing the exposure of a particular lens with that of another they own that they believe gives correct exposure.

Unless it's by 2-3 stops or something crazy, it seems to be quite a subjective assessment though. I've seen people post images to show that their lens was overexposing while others thought they looked terrific and perfectly exposed

It's always puzzled me how people say a lens is "dark" also - I've heard the 16-85 referred to as dark a few times. Does this mean it underexposes?

Click to expand...

Thank you very much for your comments. I was beginning to think that I was the only one who was seeing comments about lenses with exposure problems spoken about with suspect specifics.

Hear2see said:

Thanks for the good ideas about exposure and reading the Histogram.

The tips and cautions about being tricked by the Picture Controls and the different Picture Settings like, Neutral versus Vivid was something I hadn't though of, when evaluating the specifics of a lens' performance.

but my question was..

How are posters measuring the under or over exposure of their lenses with such specificity?

...I'm getting the distinct impression that posters may be guessing or giving impressions about their gear... instead of actual measured results.

Click to expand...

Oh. :0

Given that the metering occurs through the lens, differences in light transmission (as in T-stops) should be compensated for by the meter. But different lenses have different characteristics for contrast, giving a different impression about the tonal scale. Some of the modern nanocoated lenses appear to produce a bright image, older lenses less so. Or perhaps some just have their aperture lever just slightly off from one lens to another. Stopping down a lens with automation isn't a completely exact science.

good points Luke but wouldn't a lens manufacturer know exactly and precisely what T-stop each of their lenses have?
Shouldn't they be calibrated to work 'perfectly' ?

So a lens made to fit a Nikon camera should work without big surprises, like consistently shooting 2 stops underexposed, no?