As with the earlier postings, I refer directly to settings on the Nikon D300, but many other Nikon cameras such as the D300s, D700, D3 variants, etc. do AF-ON in a similar way.  Advanced Canon cameras sometimes call the feature AF-ON, and sometimes Back-Button Autofocus; I don’t have my own Canon to try, but at least the general advice here should still apply.

What does the AF-ON button do?

That’s simple.  Assuming you set the camera in the obvious way, the AF-ON button focuses the camera.  We’ll see later that, on Nikons at least, you’ll want to change some menu settings to keep the shutter release button from undoing the focus you set with AF-ON, but first let’s consider why you’d want to use a separate button for focusing at all.

Why bother to use AF-ON?

Here is a list of some of the reasons I’ve found that AF-ON can be useful:

• Working faster: you’d think that having a separate step for focusing would slow you down, but not necessarily.  If you’re going to take multiple pictures of the same subject, and the desired focus point isn’t going to change, then it can be faster and more reliable to set focus with AF-ON, and then fire off as many shots as you need.  There will be zero autofocus delay, and no risk that the camera suddenly decides to focus on something different as you’re trying to shoot.  Shooting a baseball batter with a long lens?  Just use AF-ON to lock in on the plate once, and fire away.
• Avoiding repeated recomposition: everyone has the experience of focusing, holding the shutter button half way down, recomposing, shooting, then going back to do it again for a second shot, and a third.  It’s slow, distracting and error-prone.  Even if you take the trouble to choose an off-center focus point (using the thumb wheel rocker), there’s still a tendency to have to move the camera a bit after focusing.  AF-ON tends to avoid repeating that.
• Being sure the focus is where you want it: slowing down can be a good thing.  Using the AF-ON button gets you to stop and think about focus before you shoot.
• Low light: this is one of the main reasons I use AF-ON.  When shooting in really low light, the camera will sometimes hunt for focus, and it can be way too dark to see for manual focus.  Flashes like the SB-800 have infrared focus assist lights that will come on as long as you are in AF-S focus mode and using the center focus point.  A great trick is to use AF-ON to get focused on something you know is about the right distance.  It can be a person, a point on the floor, whatever.  You can do this with the assist light if you like, or else by just looking carefully if the camera is locking focus without it.  Then, even in the dark, you’ll know the camera is focused there.  Even better, the camera will not go hunting to focus just when you fire off a shot.  I use this technique all the time when shooting dancers at parties or in dark clubs:  I just pick a point where the dancers are likely to be, choose an aperture that gives a few feet of depth of field, AF-ON to focus, and then snap pictures just as the dancers hit the pose I want.
• Panoramas: if you’re taking multiple shots to stich into a panorama, you’ll want the focus (and exposure!) consistent on all of them.  Use AF-ON, or focus manually.
• Using manual override: many modern lenses let you refocus the lens manually, even without setting the focus mode on the camera to M.  Without AF-ON, though, the camera will override your manual choice as soon as you press the shutter.  With AF-ON, you can mix-and-match.  With a thumb on the AF-ON button, and your other hand ready to grab the lens focus ring, you can switch quickly from auto to manual, or use manual to tune after autofocusing.  Do be careful not to hold the ring while the camera is trying to turn it though!
• Preference: some photographers just don’t like the camera focusing as they take a picture.

No doubt there are other good reasons, but that’s a pretty interesting list.  In general, AF-ON is tempting in the situations where you would use manual focus, but for some reason you need the help of the camera to lock in.

Overall, when I’m not in a hurry, I find that focusing as a separate step makes me more thoughtful and deliberate as a photographer.  More on that below, but first, here’s what you’ll need to know to get the camera settings right.

Setting up the Nikon D300 to use the AF-ON button

If you set the camera to its default settings and press AF-ON, the camera will autofocus, but there’s a problem: as soon as you press the shutter release, the camera will refocus.  So, to use the AF-ON button well, you’re probably going to want to change some menu settings.  If you’re nervous about getting your old settings back, read the posting titled:  Nikon D300 hint: Saving your Settings — it explains ways of reseting the camera, or of getting your favorite settings back.

There are various combinations of settings that make AF-ON usable, but here’s what I’ve settled on.  On the front of the camera, set focus mode to AF-S (the one that locks focus); on the back, set the AF area mode switch to Single Point.

The most obvious change you’ll want to make is to tell the camera not to refocus when you press the shutter.  To do this, find the menu item named A5: AF Activation and change it to “AF-ON only”.  Now try pressing the shutter button, and you’ll see that the camera does not autofocus;  press the AF-ON button and it will.

You might think you’re done, but there’s a bit of a problem: if you use AF-ON to focus on something, then point the camera somewhere else, it probably won’t take pictures at all!  Why?  Go to the menu item named: A2: AF-S Priority selection.  The default for that is “Focus” priority.  This setting tells the camera not to take a picture unless the object under your chosen focus point (usually the center of the image) is in focus.  In fact, if you hold the shutter release down and swing the camera back to point to the original object, it will probably fire off as soon as it passes an object that is in focus.  (That trick is called trap focusing, and indeed it can be very useful for things like getting a race car as it crosses the finish line — it’s mostly not what you want for typical uses of AF-ON).

To fix this lockout problem, change the A2: AF-S Priority selection to “Release priority”.  That tells the camera: shoot even if what’s under the focus point is out of focus.  Of course, you probably do want your subject in focus, but with AF-ON you tend to get that set long before you release the shutter, and when recomposing, the camera’s selected focus point may wind up on something else.

I put these A2 and A5 menu settings in a separate D300 Control Bank that I name AF-ON, which happens to be Bank B.  To use the camera normally, I let the camera default to Bank A.  When I want AF-ON only, I just select Control Bank B, and both settings A5 and A2 get reset.  I can go back and forth anytime.  If you use AF-ON rarely, just change the two settings manually when you need them, and then reset them when you’re done.

A bit more about low light, AF-S, AF-C, and flash

Expert readers will note that AF-C mode works with AF-ON too.  When you do this,  the camera will focus and refocus as necessary as long as AF-ON is pressed.  What’s more, because the default for a1: AF-C priority selection is “Release”, you don’t have to override that.  In most situations, there’s absolutely nothing wrong with using the camera this way;  I occasionally do, though I usually prefer seeing the camera lock focus, as it does with AF-S.

Where AF-C doesn’t work at all is if you want the aid of the focus assist light, either from the camera, or from the infrared on the SB-800.  I find that to be tremendously valuable, and it’s available only with AF-S.  You also have to be sure to select the center focus point, or else the assist light will stay off (I wish Nikon let you override that).

Anyway, I prefer using AF-S and a control bank to override both A2 and A5, but you may prefer AF-C.  Of course, if you’re shooting sports or other scenes where focus is changing rapidly, AF-C is likely the way to go, whether you use AF-ON or not.

Exposure and AF-ON

If you recompose your picture after focusing with AF-ON, keep in mind that the spot-metering mode sets exposure based on the selected focus point. Unless you also use the AE-lock function, metering will be done just as you press the shutter release. So, if you’re spot metering, you can’t forget about where the focus point is just because you’ve already focused with AF-ON.

Using spot metering with AF-ON may only come up occasionally, but many photographers will use flash with AF-ON. I can’t prove it, but my impression is that D300 flash metering also pays attention to the focus point. So, even if you use AF-ON to lock focus, when you’re actually shooting, try to have the focus point over whatever you want the flash to expose correctly (you may want to set an off-center focus point to make this convenient, and then use that with AF-ON).

In praise of thoughtful focusing

(OK, I’m going to run on here a bit, and if all you want is to learn to set up AF-ON, you can stop reading.)

What I’d like to do in closing is to emphasize a bit more the rewards of more thoughtful and deliberate focusing, however you do it. Before autofocus became widely available in roughly the 1980s, learning to focus was a skill that photographers would practice for years.  Some of that was out of necessity: taking sharp pictures in a hurry required that skill.  Some of it was the satisfaction of being good at the craft of photography and using your tools well, but ultimately it was a reflection of the fact that carefully selecting focus and controlling depth of field is as fundamental to each picture as choosing an appropriate film, composing properly, and exposing correctly.  Focusing manually makes you conscious of focus.  Do want the front eye or the ear to be sharp in that portrait?  Are you happy with the depth-of-field?  Etc.

Manual focus also has a different rhythm.  Using it encourages you to slow down, concentrate on the image you’re getting ready to shoot, maybe even think harder about other settings like exposure, Picture Control (if using a Nikon to shoot JPEGs), etc.

Of course, choosing focus points carefully is especially important when you are using wide apertures or long lenses, where depth of field is small.  Indeed, many photographers don’t realize that for a portrait taken at F2.0 with a 85mm lens on a D300, sharp focus might extend only an inch or two in front and behind the actual focus point (see the very handy online depth of field calculator).   If the eye is in focus, the nose and the ear almost surely aren’t.   Using AF-ON or manual focus can help you top stop and look at the results of your focus choice before you go ahead and shoot.

What about true manual focusing vs. AF-ON ? When I’m working slowly (and even sometimes when I’m working fast), I prefer true manual to any form of autofocus, but not on my D300.  I’ve focused SLRs manually for over 40 years, and the D300 is one of the few that just makes it hard:  the focusing screen is not tuned for it.   Even with wide aperture primes it can be a struggle to really see when focus is perfect, and with 12 megapixels, one can blow up to the point where focus has to be perfect.  (When you’re working really slowly, especially on a tripod, one way around this is to use Live View, and zoom in — that’s my preferred way of manually focusing the D300 on a tripod.)

Sometimes,  the AF-ON button can get you the best of both worlds:  the thoughtful control of confirming focus carefully, with the assistance of the camera to actually do the focusing.  Especially given the challenge of manually focusing cameras like the D300, it can be a very helpful compromise.

Still, if you get nothing else out of this post, I hope you’ll think about the pleasures of composing and focusing slowly and thoughtfully, whatever means you use.

If you found this post useful, you might want to look at or subscribe to some of the other Arcane Domain photography postings.  They’re available from the Arcane Domain Photography Feed.

In fact, many novices are discouraged from experimenting with exotic D300 settings for fear that they won’t be able to get the camera back the way they want it.  Once you’re comfortable that you can, you’ll find that some of the fancier modes of the camera (like AF-ON only for focusing) can be really useful, and playing with them can be a wonderful way to learn.

Why resetting the D300 is difficult (and why you don’t want to anyway)

This section updated, May 1, 2010: The D300 does have options to reset each shooting menu or each control menu:  you can find them near the top of the “SHOOTING MENU” and the “CUSTOM SETTING MENU”.   Use these and most of your settings will go back to the factory defaults.   There’s also something called a “two-button reset” that you get by holding down the QUAL and the +/-   buttons;  this resets things like Exposure Mode and Exposure Compensation that aren’t in the shooting banks, plus a few things like Image Quality that are.  So, with a bit of work, these techniques can get you back to the original factory defaults, at least for most D300 settings (note, however, that Nikon doesn’t provide at all for the D300 the sorts of hard reset capability that’s documented for the D100, D40, D40X, D50, D60, D70 or D80).

One problem is that to reset all the banks plus the non-bank settings takes nine separate steps, but a bigger concern is that these techniques only help if you want to go back to the the factory default settings.  A lot of the power of the D300 can be tapped only by using the many different settings that it offers.  So, you’ll almost surely want to figure out your own favorite settings, and you’ll want to get those back easily.

How to save and restore your favorite settings

There is a feature on the D300 that comes quite close to saving all of your settings, whether they’re the ones from the factory or ones you’ve chosen:   it’s in the Setup Menu and it’s called Save / Load Settings.  I’ve found that it’s the key to quickly saving and recalling your favorite settings.  If you don’t want to read this posting for all the details, just skip ahead to the section below titled: Putting it all together.

The important thing to remember is:  Save Settings saves your settings into a file on your memory card;  Load Settings restores them from there. So, you can spend as long as you want choosing settings that you like.  You can set up more than one shooting bank if you like and more than one control bank (if you don’t know what that means, don’t worry about it.)  You can set ISOs, white balances, quality settings, oddball focus control settings, etc.  Whenever you have a combination you don’t want to lose, go to the  Setup Menu and select Save Settings, and everything will be written to a hidden file on your memory card.

Now you can start changing things.  Work with different ISOs or white balances, experiment with all those autofocus modes like a2, set up for some unusual shooting situation like shooting at night, etc..  When you’re done, go back to to the Setup Menu and select Load Settings.  Bingo.  All your settings banks, for both shooting settings and custom settings are back the way they were.

Watching out for things that don’t get restored

It would be nice if absolutely everything got restored, but it’s not that simple.  First of all, there are the settings like metering pattern, focus mode (AF-S, AF-C, Manual),  etc., that are controlled by switches on the outside of the camera.  Obviously, you have to check those individually.  Furthermore, things like exposure compensation, flash exposure compensation, etc. are not saved or restored.

To find out exactly what’s saved for you, check the manual.  Here’s a rough rule of thumb that I think is close:

• If the setting is available only in a menu, like a3 Dynamic AF area, it’s saved and restored
• If the setting is available from a button on the camera but can also be set by a menu, it’s saved and restored.  Examples of this are QUAL, ISO, and White Balance.  Whether you’ve used the menus or the buttons to set them, they’re saved/restored.
• Settings that are available only from external buttons, regardless of the shape of the button, are not saved or restored. That’s why, as best I can tell, things like exposure compensation, P/A/S/M metering modes,  and flash compensation aren’t saved.  Note that these can be restored to factory defaults using the two-button reset mentioned above.

Putting it all together:  how to actually do this conveniently

If you’re new to the D300, that still probably sounds quite complicated.  In fact, most of what I’ve written above is just so you have details.  Actually using these tricks is very, very simple.  Here’s the routine I use:

Saving settings

Just play with the camera until you have settings you think you’ll want to use most of the time, and then use the Setup / Save Settings function.  An extra copy of them will be stored on your memory card, and it will stay there until you save again.  You can save whenever you want.

Experimenting or shooting in unusual situations

Change any settings you like;  you’ll be able to get back to your favorites anytime.

Restoring your favorites from the memory card

Because not everything is restored automatically, this is just a bit trickier.  Here’s what I do every time I get ready to use the camera:

• Use Setup / Load Settings to restore most of my defaults — I’ve put it on My Menu (see below) so it’s easy to find
• Look around the camera, front, top and back, to make sure the focus mode selector, meter pattern selector (spot, center, matrix), and AF-area mode selector are where I want them.  Don’t forget the Release Mode ring on the top left (the one that sets Single Frame/Continuous/Live/Self-timer) — it’s easy to miss.
• Look at the LED control panel on the top.  Make sure the exposure mode (P/A/S/M) is what I want, check apertures and shutter speeds (if not in P mode), and especially, make sure that there’s no +/- exposure compensation, or flash compensation, unless I want it.  (This third step can be done using the 2 button reset if the factory defaults happen to be what I need.)

Practice it just a bit and you can do it in under 10 seconds, and it’s an easy routine to remember.

(optional) Put Save/Load Settings on My Menu

The D300 has a feature called My Menu that you can use for easy access to the menu items you use most often.   Since I use Save / Load Settings almost every day, I put it on My Menu.  Doing this is optional:  it just saves you from working through the slightly longer Setup Menu.  If you want to do this:

• Go to My Menu
• Select “Add Items”
• Select “Setup menu”
• Select “Save / Load settings”

Now you’ll be able to find the Save / Load function in both the Setup menu and in My Menu.

Advanced technique: Using multiple memory cards

As I said above, the settings you save go onto your memory card.   If you only use one card, well no problem, but if you have multiple memory cards, then you have some choices.

I have two cards, and what works well for me is to be sure I keep the same settings saved on both of them.   Whenever I switch cards, I first Load Settings to get my defaults back into the camera, switch cards, and then Save Settings onto the new card.

A different trick that many pros use is to keep different cards for different purposes.  So, you might have a card labeled “Weddings” with all the settings you use for weddings.  Pop that one in, and use Load Settings, and you’ve got the settings you like for weddings.  Use another card for sports (all those tracking autofocus modes), etc.

In principle, if you’re lucky enough to own more than one D300, you should also be able to pass settings from one to another using memory cards.  I don’t know what the limitations are on this;  for example, I don’t know whether it’s important that all the microcodes be at the same level.  I also wouldn’t try it between different camera models (D300 to D300s) without checking with Nikon first;  I suspect it won’t work, and there’s some chance it will leave your camera in a bad state.

Also: be careful about formatting memory cards.  Just using Delete All to delete your pictures won’t affect the saved settings, but formatting the card will wipe them out.  So, before you format a card, do Load Settings to get your settings into the camera, then format the card, then use Save Settings to get the settings back onto the newly formatted card.

Advanced technique: Saving multiple profiles on your computer

Each memory card can hold only one set of saved settings at a time, but Nikon documents the name of the file, which is: NCSETUP1.BIN (actually, the manual mistakenly leaves out the .BIN extension, but you’ll see it there on the card).  If you’re comfortable enough with computers to read the filesystem on your memory card directly, you can copy that file to your computer.  That will give you a backup if you accidentally format  your memory card.  Better still, by renaming your computer files you can keep multiple files, one with settings for night shooting, another for weddings, etc.  Just be sure before you copy the file back to a memory card for use that you change the name to NCSETUP1.BIN (yes, all uppercase), or the camera will ignore it.

What about other Nikon DSLRs?

Though I have only checked using the D300, I would expect that this same technique would work at least on the D300s, the D700, D3, D3X, D3S and other high-end Nikons that offer the Save / Load menu item.

A few closing notes on D300-related postings

A few weeks ago I made my first posting relating to the D300.   To my surprise, it’s been one of the most widely read postings of the past year.  So, I’ll be trying to post a bit more on the D300 and photography from time to time.  My day job relates to computing software and the Web, and much of this blog focuses on that.  If you use a feed reader and you prefer to just see photo-related entries, you can just subscribe to the photography category of this blog.

Also, I understand there has recently been some sensitivity regarding bloggers who fail to disclose business relationships with the vendors of the products they discuss.  For the record, my only business relationship with Nikon to date has been that I’ve spent too much of my money on their cameras, lenses and flashes.  I have not received any free equipment or other such consideration from Nikon (though, if they were to offer, I wouldn’t necessarily turn them down!)

Oct 2010 update: now that you know how to get your favorite settings back after experimenting, you might be interested in the new posting:  DSLR hint:  what’s that AF-ON button for anyway?

I’ve come to depend on the fact that pretty much every digital camera I’ve ever used, from small point-n-shoots to high end DSLRs, has allowed me to see the camera’s memory card as an ordinary filesystem drive when connected through USB.  This is handy for a variety of reasons.  First of all, it lets me use a very wide range of software tools to directly access the images and other files on the memory card.  Also, when visiting with friends, it’s an easy way to hook the camera up to their computers, to leave them copies of pictures (being careful of viruses, of course.)  Unfortunately, this option seems to be disappearing, at least from some high end Nikons.

Specifically, Nikon recently announced the D300s.  It’s mostly a modest upgrade to the quite wonderful D300, but it includes some new features like video capture.  I was very surprised to find that there’s also one D300 feature that’s gone missing: the so-called USB mass storage option, which is used to expose the camera’s memory card as a USB drive.  On the D300, you can choose mass storage (to mount as a drive) or PTP, which is a special protocol used specifically for digital cameras;  on the D300s you don’t get the choice.  It’s PTP only.  Maybe Nikon did this because the D300s supports two memory cards, which means they’d have to write code to expose both of them through a single USB connection.

Anyway, if you want to copy files directly to or from the filesystem on your D300s memory cards, you have to take the cards out of the camera and use a card reader reader.  For those who do that anyway, it’s of course no problem;  for people like me who often don’t, carrying a memory card reader everywhere is a big nuisance.  I hope this isn’t a trend.