Nathan Pallace

Nathan Pallace is a photographer in Media Support Services at the Mayo Clinic Hospital in Phoenix, Arizona, where he specializes in surgical photography. He presented a session at BIOCOMM 2014 in Rochester, Minnesota about his experience being featured in the December 2013 issue of the PDN Magazine article, "What's Your Niche: Biomedical Photography".

Following is an interview with Nathan, who shares his experience working as a surgical photographer, and some tips and techniques that are unique to taking surgical photographs.

Q: When you are called in to surgery to take photographs, what is always in your "go bag"?

Nathan: My "go bag" is a black Domke with a shoulder strap and I bring it to every call I get. So much so that it has kind of become an extension of my body, or a type of appendage. Visually, it kind of makes me into an individual presence inside of an OR environment. No one else has one and everyone seems to know who I am because of it.

Every once in a while OR staff members will not recognize me when I am not carrying my equipment. Recently a colleague even pointed out that I should start paying attention to how I have incorporated my gear bag into how I move about from place to place. She described it as being a sort-of dance partner.

Since I have noticed that, I have subconsciously become aware of the bag at all times and it moves with me fluidly as I run around the hospital. I also use it as a tool to help me get through tight spaces, or block things, or even press buttons on elevators and doors when my hands are busy doing other things.

The only place that it never goes is into the sterile field. It becomes a liability there. I normally take a look at what I'm going to be shooting and then load my scrub pockets with what I think I will need before I approach the field. This makes it so that I do not have to run back and forth between the bag and the patient if I have to switch up a lens or light.

My bag contains:

• Canon EF 100 mm macro lens
• Canon EFS 60 mm macro lens
• Canon EFS 18-55 mm lens (that I never really use anymore)
• Canon EFS 10-22 mm wide angle lens
• Canon 580 EXII Speedlite with diffuser
• 6 Lacie Cool Key 36 GB thumb drives
• A Philips Full HD 1080p mini/hand camcorder (which I never really use anymore)
• Rechargeable batteries for both the camera and the flashes
• Patient note cards to collect information on that I need to archive my cases.
• Pens
• My Mayo ID and business cards
• Disposable rulers
• A Canon off camera shoe cord
• A Canon 60D or 70D rides on my other shoulder and is normally equipped with a Canon EF 28 – 105 mm and a Canon MR-14EX macro ring lite.

Q: What do you like about the Canon 60D Flip Screen?

Right now I use the Cannon 60D in surgery, but am slowly phasing in its upgrade, the 70D. The main reason these models were chosen by our department for our medical specialties is because they include an LCD flip screen option that has (roughly) a 270 degree rotational capability which you can use a live view focusing system through. This gives the shooter the option to see and shoot using the LCD screen, without having to look through the viewfinder.

The LCD capabilities also help the shooter achieve rather difficult angles that would normally involve setting up steps, ladders, or other objects to obtain working distance from the subject. In most cases I can use the flip screen system and simply hold the camera vertically over the field without even having to drop the OR table (the OR table is a big mechanical table that the patient is laid on. It can be moved up and down remotely by the anesthesiologist). To add or reduce working distance to this situation I simply have to raise or lower the camera. This style of shooting can make focusing a bit challenging, but I also see that as a fair trade to the obstacles this camera model simplifies.

In my experience, the 60D/70D saves time and makes certain OR scenarios simpler and certain other scenarios possible. This model is also able to capture high quality video as well, which comes in handy from time-to-time. My only complaint is that it does not have a full-frame sensor.

Q: In your BCA Annual Meeting presentation, you said that you use a 28mm-105mm lens, and that the 28mm-105mm lens actually becomes a 45mm-168mm after equating the 60D's 1.6 crop factor. Can you explain why you use that particular lens, and why it becomes a 45mm-168mm lens?

Crop factor is a phenomenon related to the calibration between lens sizes and sensor sizes. It is very confusing and fairly difficult to explain! Basically, all sensors are not the same size and different lenses are manufactured that calibrate correctly with these different sized sensors. When the digital revolution first started in photography, most, if not all, DSLR 35mm format cameras did not actually have 35mm format sensors/chips (FYI, the sensor/chip is the image processor in a digital camera that took the place of a piece of film). I'm not exactly sure why this is, but my guess is that it was way too expensive to mass-produce a full frame (or 35mm format) sensor in any way that would have been affordable to the average consumer (I could be wrong though). Since most camera companies have been able to manufacture their own 35mm full frame sensors (which to make things even more confusing is actually about 36mm).

I think this started happening in about 2002 (Nikon in 2005), but once again that may be a bit off. The majority of the cameras that contain these full frame sensors are still usually either pro-sumer or professional models with high price tags attached to them. Consumer models still regularly contain the smaller sensor sizes in an effort to keep prices down. So many camera companies have at least two different sized sensors and the size of the sensor is usually related to the price of the camera. The larger the sensor, the better the image resolution is expected to be (in theory).

I will use Nikon as my example from here on out because I know their product line better than any other company's. A Nikon full frame sensor is part of their FX line, while their smaller sensor sized line is called DX. You will see the letters DX or FX written somewhere on the body of any new Nikon camera or lens that you buy. So, FX cameras calibrate correctly with FX lenses. The same goes for DX to DX. The crop factor occurs when trying to image on a DX sensor with and FX lens (or small sensors and full frame lens). The DX sensor is smaller than the circle of light gathered by the FX lens and therefore completely fits inside of this circle.

If a lens and sensor are calibrated the four corners of the rectangular shaped sensor would touch points on the circumference (or near the circumference) of the circle of light let into the camera through the lens. When this calibration is off the rectangle sits completely inside of this circle of light and there is no connection to the circumference at all. The result is an inherent increase in image magnification. This is because the lens is calibrated to gather more light than the sensor can image and some of the information in the light is not imaged at all. This 'crops' the image to the size of the (DX) sensor, which ultimately magnifies it from the ability of the (FX) lens being used. Make sense? Probably not.

To break it down into more functional terms: there will be an inherited magnification to an image created when using a full frame lens with a non-full frame sensor. Therefore, the focal length (or focal length abilities when using a zoom lens) of any given full frame lens will be increased when they are used with a smaller sensor camera.

This increase in magnification is the crop factor. The only thing any given shooter needs to do to figure out this crop factor number is to Google search the specifications (specs) of the camera they have (you can look in the manual too). The manufacturer has already done the math for you. I used to use a Nikon camera with a crop factor ratio of 1.5 x. To figure out how this will configure with a full frame lens is easy. Simply multiply the crop factor X the lens' focal length (or lengths) 35 mm X 1.5 = 52.5 mm. Or a fixed 35 mm full frame lens (meaning that the focal length is always 35mm) will function like a lens with a focal length of 52.5 mm with the magnification added by the 1.5 x crop factor of that sensor.

So the crop factor on the Canon camera I use at Mayo is 1.6 x, which makes my 28 – 105 mm lens function like a lens with the zoom ability of a 45 mm – 168 mm lens (28 x 1.6 = 45 / 105 x 1.6 = 168).

I use this lens in the OR because it is versatile in the sense that I can get a fairly good amount of information in one frame using its lower focal lengths without adding lens distortions inherent with the curved glass inside of a wide-angle lens. The zoom also allows for decent close-up image at the higher focal lengths without my having to change a lens, or move my position when I am at the field. This saves time, allows for more than one photograph in certain situations, and is fairly agreeable with most of the surgeons I work with.

The reverse situation from above (using a Nikon DX lens with an FX sensor) has only recently been fixed in the last few years. Previously it simply did not work. You could not image this way. I'm not exactly sure why, but it just did not work. Now with certain camera models you can. The major issue with this being that the sensor can only image what is being projected by the lens. Therefore the entire resolution ability of the full frame sensor is not being used. Meaning, if you are using a lens calibrated for a 22mm sensor and projecting it onto a 35mm sensor, only 22mm of that 35mm will be imaged, cutting out the resolution power of the additional 13mm not being used. It makes for a smaller physical sized image with less resolution than the sensor has to offer.

Q: You also said "Lens aperture diffraction is not your friend in the OR." Can you elaborate on that? Why is it not your friend in the OR? What makes it not work in an OR situation?

Diffraction in photography is related to how light bends as it passes through a lens' aperture. The aperture inside a lens is the adjustable diaphragm that controls the amount of light traveling into the camera's body, through the lens. The larger the opening created by the diaphragm will result in the light passing through bending less. The smaller this opening is means the light is going to bend more.

Lens aperture is also closely related to depth of field (DOF), or the amount of sharp focus there is in an image in relation to the depth found in that image. Larger apertures will yield less DOF, while smaller apertures will yield more DOF.

So, the smaller the aperture equals the more potential for DOF as well as diffraction. Unfortunately these two are not allies. A visual artifact of diffraction is a sort-of blurring effect in the final image. It has the capability to make a photo look out of focus or almost as if there was movement captured when the image was taken. The more diffraction created means the more visible this blurring effect will be in the final image. Or, the more that light bends equals more blurring.

The problem is that to get great depth of field smaller apertures must be used. So the better your depth of field becomes the worse diffraction becomes. After doing some lens testing, my team and I have found that the aperture measured at the f-stop f16 is about as far as we can push our lenses and still be able to capture tack sharp photos without highly visible diffraction. If I find myself needing more DOF, I know I'm going to have to close down the aperture more, which then introduces more blurring to the final image. So you can see how quickly DOF and diffraction become a juggling act that results in sacrifices sometimes having to be made in relation to what is the most necessary element needed in the final image.

Q: How do you prepare for taking photographs in surgery? In addition to the preparations anyone else might make for being in the surgery room, what special preparations must you make as a photographer?

My preparations are fairly easy. I have to wear OR scrubs, a mask, a surgical hat or hair net, and eye protection (I wear glasses, so that qualifies). Shoe protection is also an option (basically, booties that go over your shoes), but I do not use it because I have had issues with slipping on the floor while wearing them in the past (therefore if my shoes were ever to become contaminated with blood or other bodily fluids I would have to dispose of them). Occasionally I have to wear other forms of protection like gloves, lead aprons, specific types of masks for airborne contaminates, surgical smocks, and face masks, which are always available outside the rooms they are needed in.

I am not sterile, so I also have to cover up as much skin as I can to limit the chances of hair and epithelial cells coming in contact with the sterile field. I wear a long sleeve scrub jacket and tuck it in so the loose ends never fall free. If my scrubs ever become contaminated I am expected to change into a fresh pair and sanitize the areas of my body that may have been compromised.

I'm also expected to constantly wash and sanitize my hands. I always do this before entering, and after leaving, each surgical suite while on a call. I sanitize my camera and gear with Cavi Wipes (industrial strength sanitary clothes) once or twice a week, or whenever I feel that it may have been compromised in a surgical situation.

In relation to my equipment, I make sure I have full battery power for all my components when I start the day. I also make sure that my camera settings are in place before I get my first call. This includes ISO (200), shutter speed (250, or maximum sink speed), f stop (I usually range between f 5.6 and f 16), white balance (custom). The Canon flashes that I use are changed between ETTL and manual throughout the day. From there any exposure changes depend on the situations I find myself in. I also make sure that the ring of the ring flash unit is secure to the lens so that there is no chance that it can fall off over the field. The final thing I do before approaching the field is to wrap the camera strap around my wrist several times so that it is not dangling loose while I'm taking pictures.

Q: What tips or techniques can you provide that are unique to taking surgical photographs?

The best tip I can give about working as a photographer in an OR environment would involve learning how to think on your feet at all times. This job can be very fun for a knowledgeable photographer and having a strong understanding of macro lenses and higher magnification photography is a great benefit. Every shot is not going to be close-up though, and it is important to know when you need to pull back and show a larger field.

As a general rule, most of the surgeons that I work with are regularly looking for a geographic shot that shows an exact location on the body, as well as a close-up that shows fine details. Depending on the situation in the room this could mean that the photographer needs to make a decision between using any combination of two separate lenses, or using one lens capable of capturing both of these.

Sometimes there is no time during a procedure for a photographer to take a few seconds to switch a lens, so a decision has to be made between quality and quantity from time-to-time. Learning how to make these kinds of decisions can be gathered by paying attention to the OR environments you find yourself working in. If the physicians and staff working on a case seem to be relaxed and not in a hurry it could be a good time for a photographer to experiment with two separate lenses and maybe even some alternate lighting techniques. On the other hand, if an OR seems stressed, the best thing to do is get your shots and get out of the way as efficiently as possible.

Having very solid communication skills is also a great asset in the photographer's ability to capture good images. It's important to realize that everyone is typically going to want something different. The stronger that your relationships become with your clients, the better access you will be granted. The better access you are granted, the better photographs you are going to be able to make. Sometimes it's important to know that you just have to accept that what the customer wants is not what you want and then move on.