Monthly Archives: September 2011

Achieving correct exposure

I have four friends who own professional photography labs. They are all unanimous in stating the single greatest problem experienced in their labs is poor exposure. And of course, they are expected to fix this basic photographer’s error.

So I wanted to take a moment to review exposure and what to look for in good exposure.

As we understand, good exposure holds detail in the darker or shadow end of the scale and in the lightest or highlight end of the scale as well. What this achieves is a well-balanced image without plugged shadows and blown-out highlights.

We must remember two things. First, exposure is dependent upon light intensity, the reflectance of the subject and to a certain degree, the color of the subject. And secondly, exposure measurement systems, whether hand held meters or those in the camera, attempt to make the average of any scene mid-tone.

So, the perfect solution is to measure a mid-tone photographic gray card in the light of our scene. Theory is that if mid-tone gray is accurate, all other tones will fall into their appropriate place on our histogram. Perfect! But in practical applications, we cannot always add a gray card in our scene and fiddle with exposure. Our flea will have flown and be long gone by that time!

So now what? First let’s be sure our camera is exposing properly. I am surprised that of my students, most of their cameras (75%)  do not expose accurately.

To find out where your camera exposes, shoot a photographic standard gray card in even light. Fill the frame with the card. Review the histogram. It should have a single spike directly in the middle of the tone range. If not, the camera over- or under-exposes by a certain degree. Adjust the exposure compensation until the spike is centered. This is your default error. Use that compensation in your subsequent photography and you will be more accurate.

The image below is a well-exposed gray card and its histogram. You can see the single spike in the center of the tone range. This is ideal.

Let’s look at a more difficult pair of images.

In the top image below, a common facial tissue is photographed with diffused lighting using my camera’s exposure error default. (Plus 2/3 F stop.) And knowing the tissue is lighter than mid tone in reflectance, I also opened up another 2/3 stop. This was done to place the values of the tissue correctly in the highlight side of the histogram. (Not a mid-tone gray tissue.)

Then I added the stink bug, a dark gray insect with lots of detail. With the previous corrections, this insect and the tissue on the background photographed with appropriate tone values for all components of the image.

Nikon D2Xs, Micro Nikkor 200 mm F 4.0 macro lens. SB-800 with diffuser panel.

Now the key is to standardize your own system. Know where your camera exposes. Make appropriate corrections to this built-in error. Use the default corrections when you shoot and be aware of the reflectance of the subject, making appropriate adjustments where required. All cameras and metering systems are different. And remember that metering modes, like 3D-Matrix or Evaluative, meter differently than spot or center weighted.

© Brian Loflin 2011. All rights reserved.


Why are macro lenses in many focal lengths?

My students ask me two questions when it comes to macro lenses. Why are there so many focal lengths to pick from? And, which lens do I buy?

Let’s start with the first, and the easiest question, remembering characteristics of a lens. Lenses affect angle of view, image size, perspective and in some applications, depth of field. You will remember, as the focal length gets longer, the image size increases and the angle of view decreases at any given distance. So, if you keep image size constant, you may do so from a greater distance with a longer focal length. So what does that give us?

Increased working distance!

Increased working distance is important for a variety of reasons. One, we can avoid making a shadow on our subject. We have more room for light, especially from flash. We may stay outside of the threat distance of our subject. And finally,  we can actually avoid getting bit or stung by dangerous or poisonous subjects.

The image below illustrates three Micro Nikkors: the 60 mm,  105 mm and the 200 mm. There are others from Nikon, Canon and many other manufacturers. But let’s just compare the specifications of these lenses just to get some perspective of capability.

Bracted gay feather, Liatris bracteata, Micro Nikkor 200 mm F 4.0 macro lens.

All three of these full frame (FX) lenses have the capability to focus from infinity down to 1:1 or life size on the sensor. So when reproducing a life-sized image, the 60 mm lens can do so at 8.6 inches (21.8 cm), the 105 mm lens at 12.0 inches (30.5 cm) and the 200 mm lens at 19.0 inches (48.3 cm). So in practice, an image at any given size may be made from a little over twice the distance away with each of the respective longer focal lengths.

With the longer focal lengths our angle of view is proportionately reduced as well, providing an opportunity to dissect the scene to produce a more narrow slice of life. And as a bonus, the longer focal lengths tend to be able to provide a more shallow depth of field, thus softer and more pleasing backgrounds.

So, which lens do you buy? That could depend upon price. The current price listed online from Nikon is $520 for the 60 mm; $985 for the 105 mm;  and $1795 for the 200 mm Micro Nikkor full frame (FX) macro lens. So, the rest of the answer depends upon whether you need the longer working distance, or if you need the wider angle of view. For many years my choice was the famous Micro Nikkor 55 mm F 3.5 macro lens. I used this exceptionally sharp, macro lens in my bag in place of a “normal” lens and could move in for real close-ups when needed. If I was doing an interview with an artist or chef for example, I could get pleasing environmental portraits and detailed close ups of their work with the same lens.

With tiny wild plant material, frogs, snakes, and scorpions the 200 mm macro lens is ideal. But sometimes, the 200 mm macro may be just too much lens. Remember, the angle of view is like a 300 mm lens on smaller, DX sensors. And its depth of field is very shallow.

If in doubt, try the mid-range lens: the AF-S VRII Micro-Nikkor 105mm f/2.8G IF-ED macro lens. It is one of the better lenses around and is a most useful tool.

© 2011 Brian Loflin. All rights reserved.

The details are in the lighting

“Beauty is in the details.” If that be true, then the beauty is revealed BY the lighting. I have always said, “You can’t get a great image without great lighting.” So here we are.

I have previously stated the characteristics of lighting include Quantity, Quality, Color, and Direction. When we consider these qualities, we normally think of subjects that are three dimensional and opaque. Like the natsuke in the previous posting.

Sometimes in nature and through our detail-revealing macro techniques, another concept is revealed. Many materials are translucent, or semi-transparent. Here, lighting can create another characteristic through the technique of trans-illumination. This can be thought of as pushing light through the subject to reveal characteristics of its inner structures.

This technique is relatively simple. It’s another form of back lighting, the lively light. Sunlight can work, but I find that a secondary light source like a dedicated flash works perfectly and with more control.

In the example photos below of a Morning glory leaf, the upper image is made in the normal manner. Lighting is only from the lens side of the leaf. This is a revealing image. We can visualize the color, texture and some of the smaller details of the leaf, including the veins.

In the second image below, the sun exposure is still there. But in addition, I have added a second light source directly behind and close to the leaf and aimed right through the leaf toward the lens. This is a dedicated SB-800 flash triggered from the camera with a dedicated SC-28 sync cable. Care must be exercised to prevent unwanted flare from the flash entering the lens. Cardboard, matte board or a variety of other materials can be used to mask off the unwanted light. The intensity of this light source must be somewhat greater than the top light source in order to punch through the leaf substance. This is dependent upon the thickness and quality of the leaf material itself.

In the new, lower image we can now visualize much more. The color and “feel” of the leaf is still there. This comes from the front light. But we can now visualize many more veins with greater clarity. And smaller structures, called stomata, or small pores on the leaf surface used for transpiration, can now be easily seen.

Nikon D2Xs, Micro Nikkor 60mm F2.8 macro lens, SB-800 Speedlight.
Image size: 1.0X.

This technique of trans-illumination is valuable in macro photography. From a diagnostic or demonstrative standpoint, this technique as an adjunct to top, or front lighting and cross lighting for texture can be a very valuable tool. But considering all the possibilities, the technique can take us to ways to reveal information not possible in other manners of traditional lighting.

© Copyright 2011 Brian Loflin. All rights reserved.