AE-L and AE-F

[vinestreet]

Hello,

I have a few questions about using autoexposure lock and auto focus lock effectively. I think I've overanalyzed it by reading my instruction manual way too many times, and have gone crazy.

First, I've noticed that I can still change aperture and also exposure compensation (with the dial) even with this button pressed down. If this button "locks" exposure, then why can I still change these things? Isn't exposure determined by the aperture? And the exposure compensation...that really stumps me as to how I can still change it with the AE-lock button pressed.

Second, when is the best time to use the exposure lock feature?

Additionally, the auto-focus lock feature---you can also just hold down the shutter release halfway, so why is there the need for another button? Lastly, does the type of lens I use matter when it comes to focus-lock? If I want to focus on something not in the focus area, would using a lens with better bokeh help me out more than this feature? I hope I haven't confused anyone as badly as I've confused myself.

Thank you.

[Mike Buckley]

Welcome to CiC!

I recommend that you indicate three things -- the camera model, how the button is currently configured to operate, and the type of photographs you intend to take using that configuration. People will be able to help you much more effectively.

You might want to add at least your first name and your location to your profile so that information is displayed on the left side of your posts.

[vinestreet]

Thanks Mike, I appreciate it.
I have a Nikon D40. The AE-AF lock button can be set so that it either locks only exposure, only focus, or both focus and exposure. You have to hold it down after pushing the shutter release button halfway down. My manual gives great instructions on the how-to, but I am seeking to understand more of what is happening behind the scenes and how to know when I should use this function.

For example, when the exposure is "locked" using this button, it is still possible to change the aperture and also the exposure compensation. Does this simply signify that the "locked" exposure can be overridden by changing those other settings? Also, are the phrases "metering exposure" and "locking exposure" one and the same thing?

As far as what types of photographs I want to take----I'm not entirely sure. I've been taking pictures for about three years but I'm still figuring out what makes a shot incredible versus average. I know that locking exposure can be helpful if there is high contrast in the picture and you want to make sure the subject gets the right exposure. But, I often don't know before I put the camera in front of me, what I want to do. I'm often trying to figure out what kind of settings to use, a bit too late.

[dan marchant]

In normal use the Aperture and Shutter speed are independent (but interrelated). I can set the Aperture to 2.8 and then set the shutter to any setting I want (although I may or may not get a decent exposure).

Set your camera to aperture priority mode (or the Nikon equivalent). Set your iso to 200 (and forget it). Set your aperture to any 3.5 (or whatever you desire) and EC to +/-0.

1. Now meter off a large dark object and look at the shutter speed your camera suggests.
3. Now turn to face a bright light or white wall and meter again. With the same aperture the suggested shutter speed will be much faster because there is more light available.

This is why they need to be independent because, if you specifically want/need to shoot at 2.8 you need to be able to use different shutter speeds to compensate for changes in the amount of light.

4. Meter off your dark subject again and then press Exposure Lock. You have now locked the relationship between the shutter speed and aperture.
5. Turn back to your light/bright subject and meter again and you will see that shutter speed no longer jumps to the previous high speed. You have locked the exposure so the camera will no longer alter the shutter speed to compensate for the extra light.
5. Now adjust the aperture. The shutter speed changes but it still stays relatively low. The camera is adjusting the shutter speed but only to compensate for the changed Aperture - it still isn't compensating for the extra light because you locked the exposure.

The above means that you can lock exposure but still make creative adjustments (more or less depth of field) without losing your desires exposure setting.

[jcuknz]

I have yet to use either but effectively do it the way I learnt with my digital P&S. If for instance I want to have detail in the sky which would I expect be burnt out I raise the camera and take half trigger to include more sky in the frame. Holding HT I lower the camera and complete full pressure to take the photo which if my estimation was correct will now have detail in the sky [ highlight] though maybe the darker areas will be too dark and will need to be raised in editing. IMO a lesser problem than burnt out highlights.

The drawback to this is that AF may focus on something quite wrong for the photo. This is a reason for AE lock so you can lock the exposure for the sky but then take HT again to focus on the point you want to be the primary focus point.

The reason I have yet to learn to use AE-L is that my way is so much quicker and a matter of a second or two without bothering about camera controls which I probably would forget to re-set and spoil subsequent shots ... such is my bird brain

The first time I used my version of AF-lock was when the action wasn't present and I wanted an instantatious exposure when I pressed the trigger [ I am sure you have heard about shutter delay and P&Ss ] By setting up focus on the spot where the subject would be and holding HT until it arrived I got a good action shot the moment I completed pressure on the trigger.

AF-Lock means you point the camera at something where the subject will be and lock focus while the camera is then free to work out the exposure using some other composition if you are 'fooling' the automatics and I needed to do to get what I wanted out of my basic automatic P&S. There is no reason why one should not do that with any camera in auto or semit auto modes DSLR or P&S.

There could be other situations but those are the principle reasons I have for doing it. It is so much easier and quicker to fool the automatics than fiddle with camera settings ...I guess I have been doing it for ages as when I adjusted the camera so the built in meter read above or below 'correct' depending on the subject when I used film. Above with negative film and below with slide film but also the composition of light and shade in the photo..

[Mike Buckley]

Kristen,

Now that I understand your perspective, I have what might be an unusual recommendation: Don't use that button (at least not in that way, as I'll explain below). You mentioned that you don't yet instinctively know what settings to use, so I think using the button in that way adds more complexity to a situation that you actually want to become more simple. Instead of using that button to lock in exposure, focus or both, consider simply capturing multiple images of the scene using different exposures and/or focus points. You'll also likely learn a lot more from the results after reviewing the various images on your computer.

My wife and I program the AE-L AF-L button to lock in the focus but we also configure the AE Lock with the shutter half pressed to "Off." That configuration disables the halfway function of the shutter release button. Doing so helps us grip the camera more effectively due to the pressure of the thumb working in tandem with the fingers on the same hand. It also frees us from the complication of having to hold the shutter release button halfway down without pressing it all the way down.

I'm not suggesting that you stop using the AE-L AF-L button as you have been doing so you can use it as my wife and I do. Instead, I'm suggesting that if you do stop using it as you have been doing and if the results are better photos, you could later try using that button as my wife and I do.

[vinestreet]

Dan, Mike, and Jcuknz,

Thank you for the great information!! Things make much more sense now. Much appreciated suggestions.

[vinestreet]

Dan,

The exercise you gave me was particularly useful. Thank you for taking the time to explain it all.

[Graystar]

AE Lock is very useful and the features that you noticed...of being able to change certain values...are just some of what makes it so useful.

Your AE-L has 5 possible modes of operation, but I'll only talk about three of them...the default "AE/AF lock", "AE Lock only", and "AE lock hold". Also note that Nikon cameras, by default do not lock exposure on the half-press. You can set that by changing Custom Setting 13:AE Lock. However, I would recommend leaving it as is.

The default "AE/AF lock" is used to support the "Focus & Recompose" method of shooting. With F&R, you place the subject of your shot in the center, half-press the shutter to focus, and then press and hold the AE-L button to lock focus and exposure. You now quickly reframe your scene, placing the subject where you want, and then press the shutter.

F&R with AE/AF lock is used by the rank beginner who is beginning to understand that the camera doesn't always get exposure right, and that the exposure depends on where the camera is pointing. The idea the beginner has now is that if you meter the subject, then the subject is correctly exposed. This is still wrong...but at least it's a step in the right direction. If a camera locks exposure with shutter, then pressing the AE-L button is not needed. Canon cameras work this way by default, and on a D40 the Custom Setting 13:AE Lock will enable AE Lock on the half-press...if a person should desire to work this way.

The "AE Lock only" option is used to separate the exposure lock from the focus lock. You press AE-L to lock exposure, half-press the shutter to lock focus on something else, and then reframe and take your shot. AE Lock only is used when the beginner finally learns that a good meter reading is based on the tone that's metered...regardless of whether it's the subject or not. If the subject is very dark or very bright, AE Lock only will allow the shooter to meter a mid-tone from another area of the scene for good exposure, and then lock that exposure by pressing and holding the AE-L button.

Both "AE/AF lock" and "AE Lock only" are momentary, per-shot functions where the idea is to get a (supposedly) better exposure than you would have had you simply framed as you wanted and pressed the shutter. The thumb must be dedicated to these functions, and that makes them very limited. "AE Lock hold" is the answer to these problems. With AE Lock hold you can use the same exposure for multiple shots. With AE Lock hold your thumb is freed to do other things.

When you set "AE Lock hold" you should also change another setting...you should extend the auto meter-off timer. By default, your meter stays active for only 8 seconds. You half-press the shutter and the lights in the viewfinder come on for 8 seconds and then the meter shuts off. When you lock exposure using AE Lock hold, the lock stays in place until the meter shuts off. By extending the auto meter-off timer, you can lock an exposure and keep it locked for up to 30 minutes. This is done with Custom Setting 15:Auto off Timers. You set it to "Custom" and then set the auto meter-off to 30 minutes.

With the timer set you're ready to use AE Lock hold. AE Lock hold is used when you really understand exposure, and understand that exposure is based on the light source...not the objects in the scene. Under constant-light conditions you can use a gray card or other well-known reference, such as green grass, blue sky, light skin, evergreen tree, etc. to lock the exposure. Once the metered exposure is locked you can correct it with Exposure Compensation. So you would apply +0.5 EC for a gray card, 0 EC for grass or blue sky, +1 EC for light skin, -1 EC for evergreens, etc. By locking exposure on a known reference, and applying the correct correction for that reference, you will be very close to Standard Exposure for the light source. This is the exposure you get when using a handheld incident light meter that measures the light source directly. With your exposure set you can now take images of the scene, reframing and recomposing as you wish, and your exposure will be correct in every shot as long as the light remains constant.

But equally important to the exposure remaining constant is the fact that you can now change your shooting parameters, and your exposure will continue to remain constant. If you're in A mode then you can change your aperture and the camera will vary the shutter speed to continue to provide your locked exposure. This method of shooting represents a different way to think about aperture and shutter and exposure. Instead of using aperture and shutter to control exposure, you control exposure using AE Lock and Exposure Compensation. This allows you to consider aperture and shutter only for their effect on your image. If you want a shallow DOF, you open your aperture. If you now want a deep DOF you close your aperture. Meanwhile, you're not thinking about exposure because you've already set the correct exposure. This frees you to concentrate fully on the subject and composition, without the distraction of exposure management. So you use AE Lock hold and EC to manage your exposure before you shoot, and then use aperture and shutter to control effect while you shoot. This allows for a lot of creative freedom.

[vinestreet]

Graystar,

Thank you!! You answered so many questions that I did not know how to articulate in my first post. This information helps my knowledge base immensely. I have been doing a lot of reading about tone and exposure, and although I'm still getting to a place where I instinctively know what settings to use before I shoot, knowing what my end goal is gives me the needed frame of reference.

One last thing---when you explain (your last paragraph) that with AE-lock hold on, aperture and shutter speed can still change although the locked exposure is still present--what does that mean? I have understood that aperture and shutter speed are two of the three elements (ISO being the third) that make up exposure. So if aperture and SS can be altered with AE-lock hold on, what is being "locked?"

You explained things really clearly--- and I have a lot to practice now. Thank you very kindly.

[jcuknz]

Greystar wrote ... If you're in A mode then you can change your aperture and the camera will vary the shutter speed to continue to provide your locked exposure
The Exposure lock locks you on a given exposure or EV but that EV can comprise different apertures and shutter speeds. [ and ISO for that matter]
You need to get to grips with the 'see-saw' relationship between aperture and shutter For a given exposure that you have locked on you can have a wide aperture for minimum depth of field or small aperture for greater DoF depending on the subject matter and how you want to render it.

[Graystar]

Graystar,

Thank you!! You answered so many questions that I did not know how to articulate in my first post. This information helps my knowledge base immensely.

Glad I could help!

One last thing---when you explain (your last paragraph) that with AE-lock hold on, aperture and shutter speed can still change although the locked exposure is still present--what does that mean? I have understood that aperture and shutter speed are two of the three elements (ISO being the third) that make up exposure.

I'm sorry to learn that you are another victim of the so called Exposure Triangle. The Exposure Triangle is terrible mnemonic. First, there's nothing about a triangle that relates to exposure...neither the lengths of the sides or the angles change in any proportion that relates to exposure. Second, there are 4 elements to exposure...not three. You can't have an exposure without light.

A better (but still poor) mnemonic would be a seesaw with Aperture/Shutter on one side and ISO/Light on the other side. You can change each of the four values individually. Note that most people don't think of light that way...they think the light is the light and that's that. But you can do things such as bring your own light (flash) or add ND filters to the lens (cut down the light) so you do have some control over the light. Each of the four values has a weight. When the weight of the Aperture/Shutter combination equals the weight of the ISO/Light combination, you have Standard Exposure. When you change the weight of one value, you must change the weight of one of the other three to restore the balance.

The "weight" is called Exposure Value, and I would recommend learning about it as it is a helpful concept to understand. Read this page...
http://en.wikipedia.org/wiki/Exposure_value

Skip the math...and there's no need to memorize anything. What you want to get out of that page is simply an idea of the EV values for various lighting, and a rough idea of EV values for various aperture/shutter combinations. Just knowing that interior home lighting is around 5 EV at ISO 100, and that 5 EV means a shutter of 1/8s even f/2, gives you a more solid understanding of the lighting situation and the extent of the exposure solution required (for the given example, you have to increase the ISO to 800. This increases the light/ISO EV (weight) to 8. A matching EV on the aperture/shutter side is 1/60s at f/2. Still a bit slow, but you should be able to get some sharp images under ambient light.) But like I said...there's no need to memorize anything...just a general feel for the EV will give you some sense...some appreciation...that there really is a system behind the seeming madness of exposure settings.

So if aperture and SS can be altered with AE-lock hold on, what is being "locked?"

Understanding a bit about Exposure Value addresses this question. What is being "locked"? The weight of the light. That's the only thing that gets locked when you press that AE Lock button. The other three exposure parameters are free to change. But as long as you maintain the balance, the final exposure of the image remains the same.

You explained things really clearly--- and I have a lot to practice now. Thank you very kindly.

You're welcome! Just one last thing. Practice doesn't make perfect...only practicing perfectly makes perfect. Another way of saying that is..."practice" is the application of knowledge to a task. Make sure that on every picture you take you have a clear exposure goal and a clear process that you followed to reach the goal. It can be as simple as "I want that black dog to come out black, and I'm going to base my exposure on this grayish concrete with an Exposure Compensation guesstimate." When you don't get what you were expecting, you have to go back and figure out what went wrong. That's how you get value out of practice. To just try again, without understanding what you did wrong the first time, is not practicing.

[vinestreet]

Well said, jcuknz, I definitely need to get a grip on this! Thank you!!

[vinestreet]

Thanks Graystar, yet again! I had hoped not to become a victim of anything while learning about photography---but it looks like I have. I'll have to blame my local photographer that taught a continuing ed course at a university here....I thought I could trust a professional!

[jcuknz]

....I thought I could trust a professional!

Don't be too hard on him as we all look at things in different ways and I can see a definite triangle relationship and find weight an interesting description. In my diagram I see ISO as sliding either aperture or shutter column up or down in relationship to the seat. Adding in light as a fourth variable makes it horribly complicated and really suitable for class 102 rather than 101 becuase of the extra equipment involved. I suggest a see-saw for class 101 and a diamond for 102

[Graystar]

Thanks Graystar, yet again! I had hoped not to become a victim of anything while learning about photography---but it looks like I have. I'll have to blame my local photographer that taught a continuing ed course at a university here....I thought I could trust a professional!

It's such a commonly used concept that it's practically impossible to avoid.

I see someone added a "seesaw" analogy before I made my post. That "seesaw" is not exactly the "seesaw" that I'm referring to in my description above. That's actually an additional seesaw at each end of my larger seesaw. So when I say that the Aperture/Shutter combination is on one side of the seesaw, aperture and shutter themselves are on a seesaw as well. So there are three seesaws (okay...now it's getting confusing!)

I said that the seesaw mnemonic was poor and this is partly the reason why. The seesaw has always suggested "balance" but the seesaw between aperture/shutter is not about balance with each other. Make aperture "heavier", make shutter "lighter" and you maintain balance with the other side of the larger seesaw... where light and ISO are sitting. But the aperture/shutter seesaw is itself tilted to one side...and I just never found that to be a good representation of anything. Seesaw level...okay that's balanced and right. Seesaw not level...okay that's not balanced and not right...only it IS right because there was never any balance between aperture and shutter to begin with. The only balance is between the two combinations...aperture+shutter = light+ISO. I don't know...just doesn't work for me.

That said, a seesaw style marker is great for showing the various aperture and shutter combinations for a given Exposure Value.