What is "Depth-of-Field"?

We photographers are always throwing around photo-speak terms, figuring that everyone knows what we're talking about. Some of these concepts can be baffling to the non-photographer, but that doesn't minimize their importance. Depth-of-Field is one of these.  In a nut-shell, depth-of-field describes the degree of acceptable sharpness in an image beyond, and in front of, the actual point of focus. An image with deep depth-of-field -- in a landscape, say, or a retracted smile -- looks sharply focused throughout. One with shallow depth-of-field, as in a portrait, will have a sharply defined subject standing out against a soft, blurry background. So it is something we can control and manipulate. With few exceptions, in intraoral photography we want as much depth-of-field as we can, otherwise our pictures end up with a somewhat "out of focus" appearance.
Look at these two diagrams:

Picture your macro lens -- probably it's maximum aperture (f/stop) is f2.8. That's as large as the lens opening can go. Its minimum aperture is f22 or f32; its smallest opening. Notice that when you shoot "wide open" you get very little depth-of-field, an effect even more pronounced with a macro lens. Depth-of-field increases as the size of the lens opening (actually its diaphram) decreases. Let's look at these samples:

Taken at widest opening, f/2.8 with my 100mm Macro

Taken at f8

Taken at f/32

In each case I was focusing on the very same spot, the 6th shade tab. There is practically no depth-of-field at f2.8, so although the tab I focused on is sharp as a tack, the image overall looks out of focus. At f8 we see a good deal more sharpness, but still a lot of fall-off at the extreme front and back. But at f32, the image overall looks acceptably sharp.

When I teach my workshops, I recommend that every shot be made at f32. We let our TTL flash do all the work of giving us correct exposure each time, and so we can be confident that all of our intraoral imaging will look nice and sharp. It's also a lot easier, and less error-prone, than fiddling around changing our lens setting with each shot!

Make sense? Drop me note. A sharp one, please!

Why Can't I Send A Print To My Lab?

Wow ~ it's been a busy month since I last posted, and a lot has been going on. While thinking about a new topic, I came across a couple emails from some of my client dentists asking why their labs were rejecting color prints for shade-matching, or why their percentage of re-makes were so high when they tried to use prints. A color print, quite obviously, is is a poor tool to use to convey color information to a lab.

But why should this be? After all, you have a fine digital camera and a good lens, and even an excellent color printer. The problem is not in your equipment, but in the print itself and the process of making it. Think of the limitations of that color print: for starters, it holds only a fraction of the color information that you saw on your computer monitor. An ink-jet printer, even under the best of circumstances, cannot reproduce the RGB gamut of your monitor. Plus, there is an enormous range of quality in ink-ink jet papers themselves: cheap or expensive, glossy, matte, and so on; and this all greatly affects print quality and consistency.

Now think about the process you go through to make that print. Your eyes are making decisions based upon what they see in an environment that exerts a lot of influence upon those colors. Not surprisingly, none of those conditions exist in the lab where they're trying to make sense of what you sent them. This is a truly complex subject; my most popular workshop is a 4-hour powerpoint lecture & hands-on that deals exclusively with this!

Clearly, your lab needs that color information provided by some other means. Most labs I work with prefer the images be emailed to them as jpg's. Some are requesting the dentist to actually send the CF or SD memory card itself (to be returned & re-used) so that the technician can open those images on a color-calibrated monitor in a tightly controlled color environment. If you're going to email the images, make sure you check with your lab on how they prefer them to be sent. They may have preferences on size and format, which they'll instruct you on.  Ideally you'll include in the image the shade tab and a neutralizing tab, which further help the lab determine accurate color and shading (as in the samples you see here). But make sure you don't try to "tweak" the image before you send it on. Remember, their monitors are calibrated to ICC standards -- yours are not! But more on that in a later post.

Want more info? Send me an email. And you can tweak it all you want!

Format Your Memory Card!

Has this ever happened to you  -- you take the memory card out of the camera, pop it into a card reader to download the pictures on your computer, but your computer can't find any images? You know they're there, you can see them displayed in your camera, but the computer refuses to budge. Frustrating, no? If it's ever happened to you, I'm sure you've come up with all sorts of colorful descriptions for this event - probably not printable! But what you have is a corrupted card.

There can be a number of causes for this, not least of which may be a defective memory card. Usually the images can be rescued via image retrieval software, but this can be time consuming. Formatting a card, on the other hand, may prevent the problem in the first place. First of all, it's important to format a brand new card before using it in your digital camera. It sets up the card so that it, and the camera, communicate with each other correctly. And it only takes a few seconds.

Go ahead and pop your brand-new memory card into your camera. From the camera's menu, look for the "format" function (every digital SLR camera will have this function) and hit "ok" or "go" to open it -- the open command itself will vary from camera to camera, so refer to your manual if you're not familiar with this.

You'll see immediately that you also get a "cancel" feature, which lets you opt out of this function. That's important, because formatting will permanently erase all the images you may have on this card if you've already been using it. Not an issue, of course, if the card is brand new, but certainly an important feature to remember. You don't want to accidentally wipe out your images before you've downloaded them.

So now you'll go ahead scroll the button from "cancel" over to "ok" and hit the set button to engage the formatting function. This only takes a couple seconds. And there you have it!
To re-cap: always format a new memory card. Personally, I always re-format my card before re-using it as well (instead of just deleting the photos from it) but of course, be sure that those photos have been safely downloaded first.

Do you think this will be helpful? Drop me a line! dhutt@dmddigitalphoto.com

I Love Ringflashes ~

The main technical goal of ANY photograph is proper lighting, and in our case -- macro, intraoral imaging -- this can be a little tricky. I work with dentists frequently who are trying to take their photos using all sorts of lighting sources: overhead lamps, window light,  and anything else that seems workable. Needless to say, the results from this approach are always inconsistent and as often as not produce unacceptable results. Perhaps this had been your experience, too.

First, let's talk about the Canon MR-14 Ringflash. This particular flash completes the Canon Digital Rebel SLR camera and Macro lens system. The flash unit itself attaches directly to the front of the lens, and is connected to a control module that sits atop the camera, attached to the hotshoe. It couldn't be easier to use: it's fully automatic, powerful enough to provide excellent exposure even when shooting for maximum depth-of-field, and goes where you point it.

The Nikon ringflash is called the R1 Speedlight, and although it performs the same function, with the same ease and consistency, as the Canon ringflash, it's designed a little differently. A separate ring attaches the flash heads to the lens, but they are a few inches off-axis, and are detachable and can be triggered wirelessly.  Plus, the flash controls are accessed within the camera's menu system instead of a control box placed atop the camera body. It's a very sophisticated and versatile system. The off-axis flash head configuration is perfectly suited for making all intraoral and extraoral images, but is particularly well suited for shade-matching photos which we'll discuss in a later post.

Other excellent, after-market ringflashes than can be used on both Canon and Nikon digital SLR cameras are the Metz Mecablitz 15 MS-1 and the Sigma EM-140 DG TTL.

All these flashes employ what is known as TTL ("through-the-lens") technology. This allows the flash and camera to communicate with each other in a way that ensures a perfect exposure, automatically, when you move closer or further away to frame your shot. This provides consistent, color-balanced exposures, making it possible, for example, to make identically exposed pre-and-post treatment images regardless of the length of time separating beginning and ending shots.

Need a chance to practice with these? Drop me a note & let's schedule some time together:  dhutt@dmddigitalphoto.com

A quick look at the cameras ~

It's pretty clear that the only practical way to get successful intraoral images is with a digital SLR camera, using a quality macro lens and a ringflash. This combination provides maximum image quality (color & sharpness, depth-of-field, and so on) that is not obtainable with a "point & shoot" camera.

This does not mean that you're stuck with having to buy an expensive, top-of-the-line camera. Far from it. Both Canon and Nikon produce excellent digital SLR cameras for under $1000: the Rebel XSi or T3i from Canon; the D3100 or D5100 from Nikon, for example. And there are others. I usually recommend Canon to dentists who are unfamiliar with digital photography as I find they're easier to navigate.

One of the great advantages of the digital SLR is the large lens selection. Macro lenses in particular make successful intraoral photography possible. These are amazingly sharp lenses that will provide crystal clear color-accurate images at up to a 1:1 magnification, but are also versatile enough to be great for everything else, too -- including portraits. My recommendation is the slightly longer Macro lenses like the Nikon AF 105 or the Canon EF 100.  Being slightly longer than their 60mm or 50mm counterparts, they provide the same degree of magnification but at a slightly further distance, making it possible to use a ringflash for perfect (and consistent) illumination of the entire intraoral spectrum.

A ringflash makes for a complete photography system.  Since the camera-to-subject distance using a macro lens is usually very short, any source of illumination other than a ringflash won't go where you need it! The ringflash, attached directly on the end of the macro lens, will place the light accurately and evenly on the subject: a close-up of the central anteriors, a tightly focused lateral or quad, or an extremely close shot of the #2 molar. All done simply and automatically, as these devices are all TTL ("through-the-lens") automatic strobes. Great examples of these are the Canon MR-14 Ringflash, Nikon's R1 Speedlight, and others  from Metz and Sigma.

This is just a brief, quick overview. There's so much to talk about, and of course new models of digital SLR's come about regularly. Further posts will concentrate more deeply on particular items.

What have you been using?

Welcome!

Hello & welcome to DMD Digital Photo's blog! My hope is that we can provide practical information on the techniques and technology involved in successful intraoral and extraoral photography. And of course, the real attraction of a blog such as this the opportunity to interact with you. I hope you will share your questions, your experiences, and your images.

Over the course of future posts, look forward to discussions on many topics that involve us in dental photography: different kinds of digital cameras, camera settings, shade-matching, macro lenses, ringflashes, file formation, emailing images, computer & printing issues, and much more. I would also encourage you to submit your ideas for discussions as well.

Feel free to post your comments or images here, and you're always welcome to email me directly whenever you'd like:  dhutt@dmddigitalphoto.com

Many thanks, and happy shooting!

DH