Exposure?

Now that I've read the piece, Dan, that you provided...

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Originally Posted by DanK

Whether Pluto is considered a planet is a classification, not a fact.

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Using that logic, it's a classification, not a fact, that my Nikon D7000 is a camera. To this layperson, that distinction between a classification and a fact is far less than unhelpful.

It would be far more helpful and far less disingenuous if the scientific community would admit that their facts are often nothing more than opinions because the lay community then would be able to more effectively apply the scientific information in the real world.

Bringing this back full circle to the discussion about the definition of exposure, put 100 people in a room who have never held a camera. Explain to them that their only controls of exposure are shutter and aperture. Put another 100 people in a room who have also never held a camera. Explain to them that they have three controls of exposure: shutter, aperture and ISO value. Then send those two hundred people out to take photos. I'll bet my last dollar that the second group of people will be able to make better exposures on average than the first group of people. And that's, frankly, all I care about, not the so-called accurate definition.

There is another facet that a photographer must factor into the image... The subject lightness and darkness.

We, as photographers shoot the light that is being reflected from the subject, not the light than is falling on the subject.

We measure the light with exposure meters, either built-in the camera or hand held. Some of us are pretty good at guestimating the exposure. Especially, us older photographers. I was a photographer for five years before I owned an exposure meter and I can still do a pretty good job of selecting the f/stop and shutter speed without the aid of an exposure meter.

There are two types of exposure meters and they are used in different ways.

Reflected light meters measure the light being reflected from the subject (pretty cool the way this type of meter is named:D). These can either be hand held or built-in the camera.

Incident light meters measure the light falling on the subject. These are almost always hand held. You need to have the meter in the same light as the subject or total image.

The meter can only give you an indication of the exposure - you often need to run the information provided by the meter through the computer between your ears to get the correct exposure.

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Originally Posted by MrB

The facts in Post #4 are plain, simple, and correct.

Trying to keep it simple, some simple examples, requiring no measurements, just simple observation of the information in the viewfinder or screen:

Exposure:

E.g. 1. I want to use f/11 for more depth of field for this scene; that small aperture will not allow enough light to the sensor for the camera to give a sufficiently bright image, but I can balance that by slowing the shutter speed down to 1/60s, opening the shutter for longer to allow more light to reach the sensor.

E.g. 2. I want to use a shutter speed of 1/500s to freeze the movement of this subject; that will not allow enough light to the sensor for the camera to give a sufficiently bright image, but I can balance that by opening up to f/4, a wider aperture allowing more light to reach the sensor.

Brightening:

E.g. 1. I want to use a shutter speed no slower than 1/100s with this lens, in an attempt to avoid image softening by camera shake. I also want to use f/8 to give a reasonable depth of field. However, these exposure settings will give an image that will be too dark. But I can increase the camera's ISO setting, so that the camera will brighten the image that it produces.

E.g. 2. I want to use a shutter speed no slower than 1/100s with this lens, in an attempt to avoid image softening by camera shake. I also want to use f/8 to give a reasonable depth of field. However, these exposure settings will give an image that will be too dark. But I can use my post processing software to brighten the dark image that the camera produces.

Cheers.
Philip

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Sorry Philip, you didn;t get it. I do agree with what you said in a former post.

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Much confusion arises (in many areas of life) because words that have perfectly good and simple definitions are used incorrectly, and some people cannot be bothered to change their bad habits.

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So again. In photography we use exposure as a WANTED value. It's selected before the shutter opens and is based on your iso settings or film sensitivity.

And for those who mentioned the exposure value as a quantity, again in photography it's a wanted value based on 100 iso. Based on a ev of 0 meaning an aperuture of 1, a shutter speed of 1 and iso 100.
If you use 200 iso, you have to increase that value with one, if you use 400 iso with 2, if you use 800 iso with 3.

This post is also adressed to the others who think you're right.


George

Dan,
Make 2 pictures, one with the right exposure and one with a 3 stop underexposure. You can't correct the last one.

George

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Originally Posted by xpatUSA

Brian, we need to discontinue this. None of these buttons are called "Exposure Value".

For example DP Review says:

http://1.static.img-dpreview.com/fil...pcontrols.jpeg

"Behind this are four buttons; metering mode, exposure compensation, drive mode and AF mode."

And my Sigma SD1M manual says:

" . . press the exposure compensation button . ."

If you want to confuse Bertam by calling these buttons something else, I can't stop you so I'll just shut up . . .

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I believe we are approaching this elephant from different directions.

Fine, the button is called exposure compensation. Now, if you use it and check the EXIF of the resulting image you will find that the value you set is referred to as Exposure Bias or EV and in some cases Exposure Bias (EV).

I will continue to use EV since it is the value used by the camputer or compera in managing the data of the raw file. We do not, after all, name the other values affecting exposure by the name of their control like aperture ring or shutter speed dial.

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Originally Posted by Mike Buckley

Bringing this back full circle to the discussion about the definition of exposure, put 100 people in a room who have never held a camera. Explain to them that their only controls of exposure are shutter and aperture. Put another 100 people in a room who have also never held a camera. Explain to them that they have three controls of exposure: shutter, aperture and ISO value. Then send those two hundred people out to take photos. I'll bet my last dollar that the second group of people will be able to make better exposures on average than the first group of people. And that's, frankly, all I care about, not the so-called accurate definition.

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Going along with the misuse of terms as stated in this experiment, and assuming it suggests that the second group will produce more acceptable images, the suggested outcome could well be right, but the explanation of that lies in the fact that the experiment is unfair, because the first group has been given less information:-

"Explain to them that their only controls of exposure are shutter and aperture." - this is perfectly correct. However, they should also be told, "Sometimes your chosen exposure settings for a shot might give an image that is too dark; but not to worry, a digital camera has a control called ISO - increasing that will brighten the image for you, so that you can keep those same exposure settings for that shot."

Armed with that simple bit of extra knowledge, it is likely that the first group will make just as many acceptable images as does the second group, but they will also have the advantage of a clearer and more accurate basic understanding of what it is that they are controlling and what the camera's controls do. That is without anyone having to go into the depths of the science and measurements of light and electronics.

Cheers.
Philip

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Originally Posted by MrB

....
Armed with that simple bit of extra knowledge,....

Philip

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Together that's called the exposure triangle.

George

Changing ISO at will is not a new capability.

https://upload.wikimedia.org/wikiped..._format,_1.jpg

Although I used to call it ASA.

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Originally Posted by Saorsa

I believe we are approaching this elephant from different directions.

Fine, the button is called exposure compensation.

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Thank you!

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Now, if you use it and check the EXIF of the resulting image you will find that the value you set is referred to as Exposure Bias or EV and in some cases Exposure Bias (EV).

I will continue to use EV since it is the value used by the camputer or compera in managing the data of the raw file. We do not, after all, name the other values affecting exposure by the name of their control like aperture ring or shutter speed dial.

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I was never talking about the units of exposure compensation, only the name of the control.

In view of the increasing silliness of our exchanges, I am bowing outing. Been interesting.

A parting shot:

"Many current cameras allow for exposure compensation, and usually state it in terms of EV (Ray 2000, 316). In this context, EV refers to the difference between the indicated and set exposures. For example, an exposure compensation of +1 EV (or +1 step) means to increase exposure, by using either a longer exposure time or a smaller f-number.

The sense of exposure compensation is opposite that of the EV scale itself. An increase in exposure corresponds to a decrease in EV, so an exposure compensation of +1 EV results in a smaller EV; conversely, an exposure compensation of −1 EV results in a greater EV." Glurk :confused:

https://en.wikipedia.org/wiki/Exposu...ensation_in_EV

Just above that, it actually mentions some rare cameras that DO have your "Exposure Control (EV)":

https://en.wikipedia.org/wiki/Exposu...EV_on_a_camera

Bertam might not warm to that control which reduces the actual exposure as it's setting in EV is increased.

And since "some medium-format cameras from Rollei (Rolleiflex, Rolleicord models) and Hasselblad allowed EV to be set on the lenses", I very much doubt that the definition of EV is a scientific curiosity not normally found in photographic circles ;)

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Originally Posted by george013

Together that's called the exposure triangle.

George

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Oh dear! I must follow Ted's noble and humble example and recant. Increasing ISO brightens an image and therefore it must increase exposure. It is a wonderful sunny day here and it just occurred to me that, as the Sun moves in a curved path across the sky every day, it must be orbiting the Earth every 24 hours.

Really sorry folks.....I'll get my coat.....

Cheerio.
Philip

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Originally Posted by MrB

Oh dear! I must follow Ted's noble and humble example and recant. Increasing ISO brightens an image and therefore it must increase exposure. It is a wonderful sunny day here and it just occurred to me that, as the Sun moves in a curved path across the sky every day, it must be orbiting the Earth every 24 hours.

Really sorry folks.....I'll get my coat.....

Cheerio.
Philip

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You really don't want to understand it.
Physical you're right. Exposure is the light falling on the sensor/film. It's done and you can measure it, if you're clever.
In photography it's a wanted value based on the sensitivity of the film/sensor. Do you understand the difference between a measured value and a wanted value? It's a basic understanding in measurement and control technology.
Did you ever use a lightmeter?
Did you ever correct a 1,2 or 3 stop underexposed image?
Did you ever correct a 1,2,3 stop overexposed image? That's possible too.
Did you ever work with the guidenumber of a flash?
Did you ever hear of the sunny 16 rule?
And much more.:rolleyes:

George

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Originally Posted by george013

Dan,
Make 2 pictures, one with the right exposure and one with a 3 stop underexposure. You can't correct the last one.

George

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Dan may not be able to correct the last one.

But, with my cameras, I can :D

Thanks for reminding me, Ted. I meant to upload a reply to that challenge before I left the thread. These are quick and dirty examples of my garden shed this morning:

1. Normal camera exposure:
http://i1200.photobucket.com/albums/...osure%20r1.jpg

2. Under-exposed by 5 (yes, FIVE) stops:
http://i1200.photobucket.com/albums/...ps%20under.jpg

3. Number 2 after Auto recovery in Adobe Camera Raw and a few tweaks in PaintShop Pro:
http://i1200.photobucket.com/albums/...under%20r1.jpg

The shots were handheld, hence the slightly different framing. The camera and the PC software were set to no sharpening or noise reduction. The last image at full size is quite noisy (but it is equivalent to ISO 6400). The files should still have their EXIF data, if you want to see the exposure settings, etc.

Cheerio. :)
Philip

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Originally Posted by MrB

Thanks for reminding me, Ted. I meant to upload a reply to that challenge before I left the thread. These are quick and dirty examples of my garden shed this morning:

1. Normal camera exposure:
http://i1200.photobucket.com/albums/...osure%20r1.jpg

2. Under-exposed by 5 (yes, FIVE) stops:
http://i1200.photobucket.com/albums/...ps%20under.jpg

3. Number 2 after Auto recovery in Adobe Camera Raw and a few tweaks in PaintShop Pro:
http://i1200.photobucket.com/albums/...under%20r1.jpg

The shots were handheld, hence the slightly different framing. The camera and the PC software were set to no sharpening or noise reduction. The last image at full size is quite noisy (but it is equivalent to ISO 6400). The files should still have their EXIF data, if you want to see the exposure settings, etc.

Cheerio. :)
Philip

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Cool. In my cameras, the ISO setting is passed in meta-data to the raw converter which applies the appropriate multiplier to the review image. Arvo Jagel has written a utility where you can go into the X3F raw file and edit various tags including the one for the ISO setting.

P.S. Can't read the EXIF . . .

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Originally Posted by MrB

The shots were handheld, hence the slightly different framing. The camera and the PC software were set to no sharpening or noise reduction. The last image at full size is quite noisy (but it is equivalent to ISO 6400). The files should still have their EXIF data, if you want to see the exposure settings, etc.

Cheerio. :)
Philip

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If those pictures are as you say, I must say I'm impressed. But......it's more as just brighten.

But the other part of the discussion, the exposure value in my last post, you didn't react on.

George

EV is a term which I believe started with the Rollei company (Rolleiflex Twin Lens Reflex cameras). You could use the camera's built-in meter to gain an EV value.

The EV value was a combination of shutter speed + f/stop + film speed (then measured in ASA) which would give you a "correct" exposure. You could then adjust any of the three values and the other values would adjust correspondingly. The camera was locked on a specific EV setting. You would need to disconnect the EV system to increase or decrease the exposure.

This is very much the same as today's Programmed Exposure Mode, except in that the Programmed Mode will automatically select a shutter speed + f/stop which will be appropriate for the light conditions and the ISO selected.

NOTE: all meter results should be run through the computer residing between the photographer's ears in order to be sure of a correct exposure...

As in the old Rolleiflex EV system. you can easily adjust the f/stop or shutter speed and the corresponding shutter speed or f/stop will be selected. As in the Rollei system, you can adjust the ISO (ASA) and the other two values will be selected.

As in the Rollei EV system, you need to input information (called exposure compensation in DSLR systems) in order to change the exposure which the camera automatically chooses (in P, APERTURE PRIORITY OR SHUTTER SPEED PRIORITY MODES). When you shoot in manual mode, you select the shutter speed and f/stop and changing one of those values will not change the other value.

So one EV value equates to changing the aperture by one stop or doubling or halfing the shutter speed at any given ISO.

I often shorten this and call it one-stop of exposure control despite that the exposure control may be done by adjusting the shutter speed...

Thus if I shot an image at 1/100 second @ f/8 using ISO 100 and it is underexposed by one stop (or 1 EV), I could do the following:

Open my aperture to f/5.6 - allowing in twice the light
or
Slow my shutter speed to 1/50 second - allowing in twice the light
or
Boost my ISO to ISO 200 and not adjusting shutter speed or f/stop which will double the sensitivity of the sensor and require only half the amount of light

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Originally Posted by MrB

Thanks for reminding me, Ted. I meant to upload a reply to that challenge before I left the thread. These are quick and dirty examples of my garden shed this morning:

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This just shows how amazingly broad the dynamic range of a modern camera is. One of the reasons I rarely shoot HDR any more is that I can get a decent image just by using what my camera has captured, rather than jumping through hoops with the multiple exposure / software approach.

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Originally Posted by rpcrowe

EV is a term which I believe started with the Rollei company (Rolleiflex Twin Lens Reflex cameras). You could use the camera's built-in meter to gain an EV value.

The EV value was a combination of shutter speed + f/stop + film speed (then measured in ASA) which would give you a "correct" exposure.

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I believe that the original EV value was given by Ev = log(2) (N^2/t), based on IOO ASA, and the film speed was simply used to adjust the result, thus accounting for film speed. That appeals to the pedantic mind because, once again, ISO gets removed from a basic concept :D

<>

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Thus if I shot an image at 1/100 second @ f/8 using ISO 100 and it is underexposed by one stop (or 1 EV), I could do the following:

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Ev (underexposed) = 12.64

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Open my aperture to f/5.6 - allowing in twice the light

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Ev = 11.61, so just over twice the light . .

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or slow my shutter speed to 1/50 second - allowing in twice the light

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Ev = 11.64

Until this thread got going, having never used an exposure meter, I never realized the inverse relationship between Ev (absolute EV) and exposure! Duh.

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or
Boost my ISO to ISO 200 and not adjusting shutter speed or f/stop which will double the sensitivity of the sensor and require only half the amount of light

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Theoretically the sensitivity of the sensor is not changed but I know what you mean.

It's not unusual to find such a huge gap (Ev inverse relationship) in my knowledge; a similar situation to back when I was designing and building transistor and op-amp circuits for a living but knew little about tubes (valves) because they were pasada.

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Originally Posted by xpatUSA

Theoretically the sensitivity of the sensor is not changed but I know what you mean..

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Not just theoretically, I believe. The sensor is the sensor and has a constant output level. Amplify that output and you can adjust the "ISO", with all of the known negative impacts like increased digital noise, reduced colour depth and dynamic range

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Originally Posted by GrumpyDiver

Not just theoretically, I believe. The sensor is the sensor and has a constant output level [for a given scene Lv, f-number and shutter speed]. Amplify that output [or change a multiplier during conversion] and you can adjust the "ISO", with all of the known negative impacts like increased digital noise, reduced colour depth and dynamic range

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Please pardon the additions, Manfred. Trying to account for cameras that stop amplification at some point as the ISO selection increases (some Nikons?) and, of course, most Sigmas.