Exposure Compensation- Helping The Camera Out On Tricky Scenes

Normal behavior

Cameras usually measure light to render the scene in a way that everything or almost everything will be lit and properly exposed. The way they measure light is different than it is done professionally with the use of hand held light meters (This will be discussed in another article).

They take their information from the light that passes through the lens, and based on that, they calculate the proper exposure settings in any mode except Manual; and that is because in Manual you control the exposure values, therefore the light metering is up to you.

However, sometimes you will point the camera at scenes that will contain elements that will throw off the camera and will expose incorrectly.

Tricky scenes

The camera's in built light meter measures the light in a scene based on the light reflected from the subjects in it.

However, there are colors that absorb light, that bounce it off or absorb a part and reflect another.

The camera's metering system is based on the notion that almost all colors reflect roughly the same amount of light and it calculates exposure based on that.

However, it may have happened to you that you pointed your camera at a person with white clothes with plenty of light around it and the camera underexposed the image OR you pointed the camera at something mostly black or made up of a dark color and it overexposed the image. Or viceversa.

In the first case, there isnt enough light in the shot and in the second theres too much light and the colors look washed out.

At this point you either go postal on the camera, switch to Manual or fix the photo in post processing.

All of these options are valid (except go postal on the camera, maybe) but sometimes there isnt enough time to switch to Manual and retake the shot or you dont like sitting in front of a computer for hours fixing a shot that should have come up properly the first time.

Don't panic though, there is a way to fix it right away.

Exposure Compensation

That way is called Exposure Compensation.

By exposure its meant the amount of light that will reach the sensor when you press the shutter.

Compensation in this case means to increase or decrease a value or values in order to properly expose a picture.

The values that directly affect exposure are Shutter Speed, Aperture and ISO.

So, if you are in any mode (except Manual) and you point your camera at a subject with bright colors (such as white) or dark colors (like black), the camera will think the following:

Bright colors: There is too much light in the picture, so I must select a fast shutter speed, a small aperture or low ISO in order to avoid overexposing the shot.

Dark colors: There isnt enough light in the picture, so I must select a slow shutter speed, big aperture or high ISO in order to avoid underexposing the shot.

The problem is, under this logic, the camera will underexpose in bright colors or overexpose in dark colors most of the time. It may actually not do this or it may happen that under bright colors you actually need to overexpose a bit and in dark underexpose a bit.

It all depends on the subject, amount of light available and the exposure values.

Exposure Compensation is a function that allows you to shift the exposure values and tell the camera to over or underexpose as you consider necessary.

+/-

In all Alpha DSLRs (and even in the cameras made by other manufacturers) the Exposure Compensation is represented by a button with these symbols: +/-. Usually the button is split in two; black on the plus side and white on the minus side.

In the Alpha DSLRs, this button is found at the back of the camera near the viewfinder (A100/200/300/350) or near the shutter button (A700/900).

Exposure compensation scale is based on a scale of exposure values (EV), the plus side illuminates the image and the minus side darkens the image.

When you press this button, either you will get a exclusive screen for you to move the cursor up or down the scale or the scale will light up if you use the Quick Navi screen.

As with any scale, there is a middle ground, in this case is 0, which is always the exposure recommended by the camera.

In the LCD screen looks like this:

+/-

-3 I I -2 I I -1 I I 0 I I 1 I I 2 I I 3+

In the viewfinder it will look like this:

-2 o o -1 o o 0 o o 1 o o 2+

The A700/900 go to -3 or +3, the A100/200/300/350 go from -2 to +2.

If you own a A700/900 don't worry if the scale in the viewfinder wont go to -3 or +3, if you compensate beyond -2 or +2, the camera will compensate to the value you select. The value will be displayed in the viewfinder as you select it, it will disappear once you press the shutter button, but the camera will compensate to the value you select.

Now, you may wonder why the LCD and viewfinder have I or o's between the numbers. Those are the EV steps.

EV Steps

"And what are those?" you may ask.

As I said before, the scale used to compensate its called EV scale, and the units to measure light in that scale are called steps.

As you compensate in either side of the scale, the shutter speed, aperture or ISO values change, it may be just one, two or the three of them.

The point is, whenever one of these values changes, the exposure changes.

The Alpha DSLRs have two ways of measuring in the EV scale: in 0.3 or 0.5 steps.

The A100/200/300/350 have their scales in 0.3 EV steps and the A700/900 can deal with 0.3 or 0.5 EV steps.

The I's in the LCD between the numbers or the o's in the viewfinder between numbers are the markers when you measure in 0.3 EV steps, but when you measure in 0.5 EV steps, the marker is placed between two I's or two o's.

0.3, 0.5, 0.7

So what's the difference between 0.3 and 0.5 EV steps?

The basic difference is the amount of steps you can compensate.

In 0.3 steps, the scale goes like this:

-3, -2.7, -2.3, -2.0, -1.7, -1.3, -1. -0.7, -0.3, 0, +0.3, +0.7, +1.0, +1.3, +1.7, +2.0. +2.3, +2.7, +3

In 0.5 EV steps, the scale goes like this:

-3, -2.5, -2.0, -1.5, -1.0, -0.5, 0, +0.5, +1.0, +1.5, +2.0, +2.5, +3.0

When you use 0.3 EV steps, the scale is larger because you can access 0.3 and 0.7 steps of compensation between numbers.

When you use 0.5 EV steps, you can only access halves between each number. The scale is smaller.

Differences between 0.3 and 0.5 EV steps

Now, if you use a A100/200/300/350, you dont have to worry about 0.5 EV steps because you can't access them, but if you want to know the difference between 0.3 and 0.5 scales, keep reading.

For those of you using a A700/900, there are differences when you use 0.3 or 0.5 EV step scales.

The use of both scales presents tradeoffs. Using a 0.3 EV step scale allows you to use a bigger scale whereas 0.5 is more limited.

The difference is that if you need precise increments, 0.5 EV works a lot better than 0.3 EV, because 0.3 EV presents you subtle changes that wont affect too much the exposure in case you screw up, but it will require you to use more steps to make a visible compensation. And thats another tradeoff, if you want subtle changes without introducing a harsh change in exposure, 0.5 EV wont work for you since that's what it will do, the changes will be more visible, so if you want just a slight touch of more light into the picture, 0.5 EV won't do the job since it will introduce more light in each step than 0.3 EV.

In 0.3 EV, the lack of a middle point between steps is compensated by the fact that you can use 0.7 EV as well, and that step may introduce enough light to make a difference or a little too much. It all depends on the scene.

In 0.5 EV the changes are more predictable, so if you require a visible change and you know how much, 0.5 EV will work better than 0.3 EV since it won't require you to decide whether to use a 0.3 or 0.7 step compensation, it will be just a half and you can learn what to expect. However, if you rather make exposures where the light is increased or decreased in a more gradual manner, chose 0.3 EV.

There is one more thing to keep in mind: the scale you chose for Exposure Compensation also affects the shutter speed and aperture range. If you chose 0.3 EV, the shutter speed and aperture will change in values of 1/3rd whereas if you chose 0.5 EV, the values will change in halves.

This is done in order to match the changes introduced in 0.3 or 0.5 EV steps.

And again, there is a tradeoff, having the speed or aperture shown in 1/3rd gives you a broader range of speed and aperture (limited by your camera's top speed or lens' aperture range) but it will take longer for you to get to the setting you want, which wont happen if you use 0.5 EV.

It's up to you which scale you use; 0.3 or 0.5 EV.

To change between those two in the A700: Menu-> Recording Menu (camera icon) Page 1-> Exposure step-> 0.3 or 0.5 EV

In the A900: Menu-> Recording Menu (camera icon) Page 2-> Exposure Step-> 0.3 or 0.5 EV

Notes of use and Closure

• The primary function of Exposure compensation is to illuminate or darken an image when the camera doesn't expose correctly because its pointed at a subject or scene mostly made of white or black.
• Exposure Compensation is useful, especially since Auto Mode tends to underexpose sometimes.
• It must be used with caution since it can ruin a photo if not used properly. Use only as much as you need to get the shot you want, if you over do it in any part, you may do a worse mess than the camera's.
• For pictures that require a drastic and precise compensation, use 0.5 EV, for pictures that require subtle and gradual changes use 0.3 EV.
• It doesn't work in Manual Mode, but will work in the rest of the modes, even Scene Modes.
• In Manual Mode, the Exposure Compensation scale changes to M.M.; which means Metered Manually, the camera still offers its opinion about the proper exposure to chose but the final choice its up to you and you can ignore the camera's recommendation.
• There is more range in compensation in 0.3 EV than in 0.5 EV, but in 0.5 EV the changes are more visible in each step.
• For some weird reason, in the A700 happened that when using Exposure Compensation; the exposure values DIDN'T change BUT the illumination in the picture DID change a bit.

Exposure Compensation is a useful tool when you're shooting in P,A,S or any Scene Mode (except in the A900, it doesn't have Scene Modes) and the shots aren't coming properly exposed. It allows you to do a quick tuning and let the camera do the rest, you just tell it how bright or dark you want the picture to be regardless of what it thinks.

This function will save you time in front of your computer and will give you more time to take more pictures.

One final advice: I strongly recommend you conduct experiments of your own with this function so you learn the changes it introduces in a picture and how does the camera behave when you use it, this way you will learn to know what to expect from this function and will give you a solid idea of how much to use and when to use it.

Lens And Sensor Contamination

This article will give you an insight on why and how your lens and sensor can get dirty, the following articles will be reviews of items I've personally tried that help you clean these two parts and some more.

What causes that a lens/sensor gets dirty?

The front element of a lens is the part exposed to the environment when shooting, and unless you use a protective filter above it, it will get dirty at some point.

Dust, liquid stains and fingerprints are the usual reasons of why a lens gets dirty. Unless you're doing something you shouldn't be doing with a lens, there may be other reasons, but those three are the most common.

In a sensor, the most common trouble is dust. Dust is everywhere; except in a sterile, air locked room. But you're not going to live or take pictures in a room like that, you will shoot everywhere and anywhere, and dust will be around.

So how does dust falls on a sensor?

Everytime you change a lens, you expose the mirror box and dust particles have a chance to get inside it. Once you turn on the camera, the shutter will open every time you take a picture, revealing the sensor and dust will have a clear path to attach to it. The problem with sensors is that they are electrical devices, therefore they generate static electricity, which attracts dust particles.

Unless you work with small apertures (f/16,22,32) you wont see if there is any dust on your sensor, however, you shouldn't just ignore the issue and let it keep going, the more dust your sensor has and the longer it has it, the more difficult it will be to remove it, since the dust will get electrically charged and practically bond with the filter.

Other sources of contamination are liquid stains if you attempted to clean the sensor with liquids or if you touched your sensor with your greasy fingers as I told you NOT TO.

Cleaning options

There are a LOT of ways to clean a sensor and a lens, but depending on how skilled and experienced you are, you may end up making a worse mess than you already have.

The problem is that, if you do it wrong, you may practically ruin your lens or your sensor. How much it cost you one or both of them is what determines how big of a mistake you can do.

In lens cleaning, the most common options are liquid and tissue or a cloth. In sensor cleaning the main go to options are the wet method; which consists of custom made swabs and a special solution to clean the sensor or the dry method which consists of blowing air into the sensor.

Before going any further, I should clarify that you don't actually clean the sensor itself, but a low pass filter in front of the sensor. The sensor never gets touched, but the filter. It's common practice to refer to the sensor because that's what you basically look at when cleaning the filter. Back in the dawn of digital age, DSLRs didn't have a filter in front of the sensor and makers weren't aware of the dust problem, so sensors would end up getting REALLY dirty, and the solution they came up with was to put a filter in front of it along with a vibrating mechanism to dislodge any dust that fell on it.

The Sony Alpha DSLRs contain this vibrating mechanism which is helpful to remove dust, but for that stubborn dust that wont go away, there are options.

The key point

The most given advice when doing sensor cleaning is:

IF YOU DO NOT TRUST YOURSELF TO DO THIS, DO NOT DO IT, TAKE YOUR CAMERA TO AN AUTHORIZED SERVICE CENTER.

We will establish this as an axiom.

Possible problems of different cleaning methods

For lenses:

Liquid and tissue: If you use more liquid than necessary, you may spill it inside the lens and leave stains on the glass.

Other problem of this method is that you rub against the glass with a liquid, which in turn, affects the coatings the lens or filter may have on them. You may wear off the coatings if you use this method frequently or with liquids not meant for optics.

Soft cloth: Even though there are cloths specifically designed for lens cleaning, there is 1 big but to this method.

This method will work great once, maybe twice, but then it will become a danger for your lens and here's why:

You touch the cloth with your FINGERS, which in turn are full of SKIN OILS, and those end up in the cloth, so the next time you use it, you'll end up smearing the lens with them.

You may think "Well, Ill just put it in the washing machine and get rid of those skin oils".

WRONG, this will only make matters worse. Water has calcium, calcium is a type of crystal mineral that can scratch your lens.

Air blower: This method is safe but it's not a panacea (a solution for everything). It will get rid of dust in your lens, but not from smudges, finger prints or sticky dust. If you got a lousy blower, it may not even blow enough to remove dust.

For sensor:

Wet method: If done properly, this is a very effective method to remove dust and any other stuff that doesn't belong in the sensor. The problem is that, if done wrong, you can leave smears or actually move the sensor out of place if you press too hard.

Usually the wet method is done by people with enough confidence and skill when everything else failed. But this shouldn't be attempted by rookies. You should train first simulating the procedure on glass or other similar material that wont be ruined if you screw up.

The problem of the wet method is that you can't do it quickly, materials are somewhat expensive and requires a clean, steady place to do it. Not to mention time, patience and great hand control.

There is one issue to keep in mind: sensor cleaning liquid is flammable, so forget about taking it on a plane; high pressure and flammable liquids: not a good combination.

There are plenty of liquids out there that can be used to clean a sensor using the wet method, but there is only ONE that's allowed by Sony to clean the sensors on the Alpha DSLRs that wont affect the low pass filter protecting the sensor.

The liquid is: Eclipse E2 Solution

DO NOT USE ANY OTHER LIQUID BUT THAT ONE. If you use any other liquid, it that may corrode the filter and even the sensor.

To learn how to do a wet cleaning, click here and here .

Air blower: This is the default recommended option suggested by camera manufacturers to clean your sensor. But for it to work, you need a good enough blower, a flimsy one wont do much.

They recommend this method because you don't really touch the filter, therefore you can't do something which will ruin the camera.

The problem with this is that not all dust responds to it, some electrically charged or mold dust sticks to the sensor and needs physical contact to remove it.

WHATEVER YOU DO, DO NOT NOT NOT PLACE THE BLOWER'S NOZZLE RIGHT ON THE SENSOR AND DO NOT USE BULB (SHUTTER SPEED) TO CLEAN YOUR SENSOR. IF YOU USE BULB AND YOU TAKE YOUR FINGER OFF THE SHUTTER WHILE THE NOZZLE IS AGAINST THE SENSOR, THE SHUTTER CURTAINS WILL CLOSE AND CRASH AGAINST THE NOZZLE, EFFECTIVELY RUINING YOUR CAMERA FOR GOOD.

If you got a strong enough blower, it may even remove that dust, but if it doesn't

DO NOT NOT NOT NOT NOT NOT EVEN THINK OF USING CANNED AIR.

Canned air is great for cleaning computers, but computers don't have sensitive material that you may end up screwing up by THE TINY PARTICLES THROWN BY CANNED AIR.

Canned air has been proved to contain rubber particles and other garbage inside the can, and if you use this to clean your sensor, you will just pass them on to it. DO NOT USE CANNED AIR FOR SENSOR CLEANING.

It's just as bad as putting some scotch tape on the sensor and pulling it. Sure, you will remove a lot of dust and whatnot, but you ll leave glue on the filter. IT'S JUST PLAIN SILLY.

Closure

Sensor and lens cleaning is an easy process, the scary part is that if done wrong, it can ruin your sensor or lens. There are many ways to do something wrong and a few (if not only one) to do it right. Again, if you don't trust yourself enough to do this process, take/send it to your camera's manufacturer service centers or places that know what they are doing like Adorama and Calumet Photographic .

There are a lot of methods to clean a sensor and a lens, some are the best way, some are just nonsense and very risky. On this article I discussed the most common methods to clean a lens and a sensor and their possible problems.

On the following two articles, I will review two products Ive recently used to clean my lenses and my sensor that yielded perfect results.

Human Grease-A Camera's Worst Friend

If Alpha DSLRs were capable of dreaming, one nightmare that all of them would have, would be of being chased by a human hand trying to touch it in places not designed to be touched.

A bad friend

Human contact is mandatory in order to operate a DSLR. Sure, you can shoot in tethered mode and not touch the camera, but that wont give you much options for angles, and either way, you got to touch the lens to select the focal length.

DSLR bodies are designed to endure the abuse of human contact, but other parts are not.

One of the things that any DSLR or P&S camera fear a lot (if not the most) is the grease from human hands.

Enemy profile

Human skin secretes oils to keep the hands lubricated, some people secrete more oils than others, but everyone does it.

Human skin also removes waste from the body, around a 30% of all the waste a human body can generate. That means that the oils can also contain whatever your body is getting rid off through the skin.

These oils can taint or smudge a lot of surfaces. Usually you can clean them easily, like if you press your hand against a glass, a wipe with a cleaning product and a rag leave no trace of it.

But the same can't be said of photographic equipment.

Stay away!

If there are surfaces sensitive to human grease, those are surfaces of photographic equipment.

Due to the fact that you need to use your hands and fingers to control the camera, inevitably at one point or another you will touch your lens surface or something even more delicate, leaving your mark on them.

Unfortunately, cleaning these parts is not as simple as cleaning a window, since they are delicate, if you use the wrong product, you can need a replacement of that part or you can ruin your equipment. LITERALLY.

These are the parts of a camera that you should NEVER touch with your greasy fingers:

• Camera sensor
• Lens front or rear glass ends
• Focusing screen
• Mirror chamber
• Lens contacts (in the mount and in the lens)
• Built in flash
• Viewfinder
• LCD Screen

These parts are the most sensible to skin oils, most of these can be cleaned, but they require careful procedures, because if you dont do them correctly, like sensor cleaning, you can ruin it for good. Focusing screens for example, can be replaced, but you got to send it to an authorized Sony repair center. If you have an A900, you can do it yourself, but be careful.

Advice

If you clean your camera, even if its on the outside, ALWAYS ALWAYS ALWAYS use latex gloves, like the ones doctors and surgeons use. They are sold in stores like Wal-Mart in the house cleaning section or in a store that sells medical supplies. These gloves will prevent your oils to touch delicate parts if for some reason you make a mistake or your hand slips or whatever.

A method Ive read about with no complaints so far is the use of the
LensPen system. In few words, its a brush that you gently move around your lens and will clean your fingerprints and other contamination without leaving trace. They have also a brush called SensorKlear thats design to clear sensors as well (CCD and CMOS) in the same fashion. Ive ordered one of each of them, but I havent received them yet. But all the research I made didnt yield reasons not to get them. They offer producs for cleaning lenses, sensors, cellphone cameras, LCD screens and TV screens as well as monitors. I suggest you check that site.

If you stain one of the parts I listed and you do NOT know what to do, DO NOT NOT NOT attempt to clean it with what you would normally clean skin oil stains like water. Research thoroughly first and determine whats the best course of action, if the cleaning procedure seems too complicated or you dont feel up for it, DO NOT proceed with it, look for a professional service such as offered by Adorama or Calumet Photographic.

Never send your equipment to unauthorized repair centers, the procedure done there may void your warranty and increase the problems your camera has, and the manufacturer may not want to repair your camera or it may be too expensive to repair.

Buy a LCD screen protector. Sony offers one for every Alpha model in the current lineup, and you can find third party solutions as well. The protector will keep your LCD screen safe from scratches and smudges. It's easier and cheaper to replace a protector than the whole screen.

If you attempt to clean your mess yourself, make sure the products you will use are compatible with your camera. This applies especially to sensor wet cleaning method. The only liquid solution approved by Sony for sensor cleaning in the Alpha line is the Eclipse E2 Solution. Use of another solution may corrode or stain your sensor filter.

Closure

You may have suspected it, but now you know it for good, human skin isnt the best friend of your photographic gear.

If you are careful about your gear, you shouldnt run intro trouble, but if you do, there are options to clean the mess or repair it.

It's better to be cautious and safe than being sorry, I recommend you follow the guidelines laid out in this article.

And again, if you stain something and you don't know what to do, do NOT think of "brilliant and original" solutions. There are a 1,000,000 ways to do it wrong and a few ways to do it right, if you don't know what to do, don't act impulsively, instead follow this sequence:

STOP->CALM DOWN->ANALYZE THE PROBLEM->RESEARCH FOR SOLUTIONS IN THE INTERNET OR IN PHOTOGRAPHY FORUMS->EVALUATE PROS AND CONS->DECIDE AND EXECUTE THE SOLUTION YOU CHOSE

Your gear is delicate and precise equipment, therefore it requires proper care.

Take care of it and don't lay your greasy fingers on sensitive parts.

Shooting In Low Light, Where Did My 5fps Go?

The following is a problem that affects the A700 when shooting in low light.

On this thread at DPR Sony SLR Forum forum member JUMPH asked a question that I think its worth to post in here for future reference if anyone else has the same problem.

He mentions problems with his A700, when shooting in low light conditions (he lists sunset or indoors at night as his examples) the camera wont fire at 5fps, but at 2fps.

He mentioned how he tested the camera using shutter speeds from 1/60 to 1/8000 and shooting with no memory card. In theory the speed he tested the camera at its enough to achieve 5fps, but he couldnt get them.

He shot this video to show how the camera would only go to 5fps if he used a bright light source pointed at the Eye-Start sensors.

Originally I thought that the problem was the shutter speed used or the memory card. But I was wrong.

According to forum member Ken_5D, the problem is that the AF is taking longer to confirm focus in low light. This makes sense since digital sensors do not see light as the human eye does, so a low light for us is dark to them.

He mentioned two possible ways to get around this problem:

1.- Use Manual Focus
(I told you, you will need to learn how to use it ;) )

Or

2.- Set the shutter to Release

Or

3.- Point a light source to the Eye-Start sensors.

So now you know, if you come across this problem, these are your options to get those frames per second back.

Finally, there is a thread in Dyxum forum that talks about this problem in great extent

Until next post!

System Reset And Another Tip

I found this on a thread in DPR's Sony SLR Forum.

A forum member had a problem with her A300, that just displayed half a picture. It looked like the shutter was broken.

She received help from Sony and they gave her some instructions that seem to have solved her problem.

Im posting the instructions here in case someone who reads this blog ever has a problem with a Sony Alpha DSLR and this may help.

System Reset:

1.- Turn camera OFF

2.- Take out memory card

3.- Take out battery

4.- Turn camera ON for 30 seconds and then turn OFF

5.- Put battery back in

6.- Turn camera ON and go through the menu until you find the option RESET DEFAULT

Hopefully this will work when you dont know what to do.

Another solution I know from personal experience that applies to most electronical devices when they start acting weird is:

1.- Turn device OFF

2.- Remove battery or unplug power cord or disconnect battery (in case you cant remove it)

3.- Wait from 20 to 30 seconds

4.- Put battery back in, plug power cord or reconnect battery

5.- Turn device ON and check if that solved the problem

This usually solves most problems related to weird operation AS LONG AS THE EQUIPMENT ISNT PHYSICALLY DAMAGED OR HASNT BEEN TAMPERED OR INTERVENED.

If the problem you're having persists, you need to contact customer support. On the link list to the right youll find the eSupport site from Sony that will redirect you to the proper site depending on your location.

Source For System Reset