Monthly Archives: December 2014

Why do macro lenses come in several different focal lengths?

Which one do I need?

TX Bluebonnet-3560-Sm

Texas Bluebonnet, Lupinus texensis. This flower was photographed  at half life size on the sensor (0.5X) with a Nikon macro lens. Which focal length was used?

True macro (or Micro) lenses allow subjects to be photographed much closer than normal minimum focusing distance, thus greatly magnifying the image size. Often, these are prime lenses of single focal length with various focal lengths available from each manufacturer. And macro lenses produce high quality images. Because these are complete lenses that focus to infinity, many other uses of high quality are possible.

Macro lenses are the more expensive of the alternatives to focusing close. Most retain all automatic features, but have limited magnification range, frequently up to 1:1, or life size. With accessories they can produce magnifications from 1.0 X to 40.0 X life size. Because no lens extension is required per se, little exposure compensation required.

Most manufacturers make more than one macro lens. Canon, Nikon, Olympus and others produce high quality macro lenses. True macro (or micro by Nikon) lenses are produced in various focal lengths, commonly from 40mm upwards to 200mm. And they may all focus very close; most focus to life-size or 1.0X. (Also called 1:1.) Essentially, they all do the same thing.

_BKL6994-Sm

Three Nikon macro optics (clockwise, from near left) 60 mm F 2.8 AF Micro Nikkor, 200 mm F 4.0 AF Micro Nikkor, and 105 mm F 2.8 AF VR Micro Nikkor.

So if that is true, why would there be a variety if they all do the same thing? The answer is simple: working distance. Working distance is the actual distance between the subject and the camera’s sensor when the lens is focused. As the focal length of the lens increases, the working distance also increases at the same image magnification.

Let’s look at the working distances provided by three popular focal lengths above: the 60mm, 105mm and 200mm macro lenses. All these lenses below are accurately focused at life size or 1.0X and the reproductions are at the same scale. Canon has lenses in similar focal lengths; the 60mm F2.8, 100mm F2.8 and the 180mm F 3.5 lens trio. All are magnificent optics to be sure.

Nikon Macro Lens

This lens is the 60mm F2.8 Micro Nikkor focused on a small portion of the flower at life-size. It focuses to 1:1 at 8.6 inches.

Nikon Macro Lens

The second is the 105mm F2.8 Micro Nikkor. It focused to 1:1 at 12 inches.

Nikon Macro Lens

This last lens is the 200mm F4.0 Micro Nikkor. It will focus at 1:1 at a distance of 19.2 inches.

Working distance is important to macro photography. Greater working distance allows several advantages. These include the freedom from making a shadow on the subject, the ability to get ample light or lighting fixtures onto the subject, the ability not to frighten or run off a live subject and the ability to work at a safer distance from a dangerous subject.

One additional attribute to remember is that the angle of view of any lens gets smaller as the focal length increases. So as a result, a 200mm lens focused at 1:1 will have an area of coverage of one half that of a 100mm macro lens at the same magnification.Three Focal Lengths-Sm

These three images were made with the macro lenses described above.  In making the photographs, emphasis was given to producing the flowers at the same size in each frame in the camera when shot. To do so the image with the 60mm lens is made from fairly close; the 200 mm lens much farther away.

The resultant images look the same, but upon close inspection there are notable differences. First, the longest lens tends to compress the image more than the other two. The distant flower looks closer to the close one. This is an example how the focal length of the lenses affects perspective. The second difference is an apparent difference in angle of view. Notice the black form in the upper right of the images. We see less of it in the 60 mm view and it tends to move and get larger as the lens focal length gets longer. Otherwise, there is little difference perceived in the three images. Because the subject size is the same in the three images, the Depth of Field is also the same. All images were shot at the same F5.6 aperture.

So, to answer the question: The lens that’s right for you depends upon your most common use. If you need a lot of accessory lighting like flashes, diffusers and other modifiers in your set up, you may enjoy the freedom of the longer focal length/longer working distance. If you want a real compact lens, then the shorter lens may be perfect. A good compromise and my recommendation is the 105 mm F2.8 AF VR Micro Nikkor.

Copyright © 2014 Brian Loflin. All rights reserved.

 

 

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My customers make great photographs. You can too!

Goluch Jays

This is a recent image made at my South Texas Bird Photography Workshop by Denver photographer, Richard Goluch. A repeat customer, Richard shot this aggressive pair of Green Jays from one of the permanent bird blinds at my last workshop in October. The jays always make good subject matter, but Richard was able to take it a step further, catching the in-flight squabble. Well done, Richard!

Workshop participants often return for an additional season. Here is a note from another repeat customer:

“Brian is a great teacher and host. He wants you to be successful and goes to great means to make sure that you are.  I really liked the ranch and the atmosphere of the hotel. “ G. Payne- Arkansas

My South Texas workshops are three to five days long and prices are most reasonable, including all meals, lodging, instruction and ranch fees. Our ranch has four purpose-built bird blinds, each with permanent water features, automatic feeders and plenty of birds. Additional, specially constructed blinds for shooting raptors provide added exciting and action-filled photographic opportunities. South Texas specialties like the jays above are plentiful.

Crested Caracara

Incoming Crested Caracara landing at the raptor blinds. Nikon D800, Nikkor 80-200 mm F 2.8 lens with 1.7 teleconverter. This is an ideal setup for shooting on this ranch. Many of the birds are 12-15 feet from the blinds. Raptors, about 15 yards.

Workshops are planned to take advantage of both spring and fall migration. The species count is now at seventy-seven species photographed. There are two slots remaining for the next workshop in late February, 2015.For more information, please see: www.thenatureconnection.com/SoTxBirdPhotoWS.html .

Copyright © 2014 Brian Loflin. All rights reserved.

Understanding the myth of “Crop Sensor” cameras.

Why crop sensor cameras do not produce greater subject magnification than their full-frame brothers.

I am disturbed by a lot of talk over the last few years stating that cameras with “crop sensors” produce larger in-camera subject size to cameras with full frame sensors. This thinking is both incorrect and continues to mislead the photography world. I feel this misleading language comes from two camps: One, the marketing folks who try to tell us that with a 1.6 crop sensor our 200mm lens is now a 320mm lens. And two, the wildlife photographers who want large in-camera images and who use a crop sensor camera believing the crop sensor somehow produces greater subject magnification.

Let me provide a couple of examples of that talk:

“For nature, wildlife and sports enthusiasts, it might make more sense to stick with a smaller sensor. You can take advantage of the crop factor to get maximum detail at long distances.” http://digital-photography-school.com/full-frame-sensor-vs-crop-sensor-which-is-right-for-you/

 “…the Mark IV has the 1.3 crop factor and a higher megapixel count than the D3s, which are nice for telephoto work.” http://www.deepgreenphotography.com/the-gear/

 “Focal length measurements on lenses are based on the 35mm standard. If you are using a crop frame camera the sensor is cropping out the edges of the frame, which is effectively increasing the focal length. The amount of difference in the field of view or focal length with a crop sensor is measured by its “Multiplier.” And,

 “…while a crop sensor DSLR doesn’t provide the same level of image quality as a full frame DSLR, it does [offers] sic. major advantages when it comes to cost. It can also be very effective for telephoto photography for the extra reach gained from the crop sensor multiplier. For example, this can be very useful when shooting sports, wildlife, and other types of photojournalism…” both from: http://www.slrlounge.com/school/cropped-sensor-vs-full-frame-sensor-tips-in-2/

 First let me state two facts: One, images from crop sensor cameras are not inherently of lower quality than those of full-frame cameras and, two, crop sensor cameras produce exactly the same in-camera image magnification as do their larger full-frame brothers.

Before I take this discussion of why these facts are true, let’s understand some things about cameras and their sensors.

First, a full-frame sensor gets its name from the fact that is physical measurements are, in round numbers, 24 x 36 mm. That’s the same size of our old standby, the full-frame 35mm film negative or transparency.

Second, I truly believe that the term, “crop sensor” is a misleading term. It is simply a sensor that is smaller than the full frame cousin. And there are now several sizes of “crop sensors”. They range from the APS-C (15.7 x 23.6 mm), the APS-H (19 x 28.7 mm), four thirds systems (13 x 17.3 mm), and even smaller. So there is really no “Standard” when it comes to identifying a sensor size.

Now let’s talk about the lens for a moment, the image forming device that projects our picture on to the sensor. Lenses have several characteristics. They affect:

  • Image size. This is governed by the focal length. Longer focal lengths produce larger subjectdetail on the sensor at any given distance,
  • Angle of view. This is the area of coverage in front of the lens that the lens may capture and project on to the sensor. It too is governed by focal length. Shorter focal lengths produce a wider angle of view that longer focal length telephotos for example. And finally,
  • Perspective. This is a relationship of components within the image to others within the same image. Focal length affects perspective, but only when the lens-to-subject distance is changed.

Crop sensor-Example 1

Let’s look at the image above to understand the physical relationship. The large frame is that of standard 35 mm film and also that of a full frame digital sensor. The yellow outline represents the area and magnification of an APS-C sensor, similar to that of a Nikon D2X or D7100 series camera body. The image was taken with a Nikkor 80-200 mm F 2.8 zoom lens.

Lenses have physical characteristics in addition to the optical characteristics above. One that is most important here is lens flange-to-sensor distance. This is the physical distance from the rear mounting flange of the lens to the sensor. That distance is specific to allow the lens to be focused at infinity. This distance is somewhat different between manufacturers, but it is standard within a manufacturer family so that all lenses will work properly.

In order for a lens of any particular focal length to produce larger image details on the sensor, the lens must be moved farther from the sensor or closer to the subject. Since the flange-to-sensor distance must be the same for cameras of a particular brand, any given lens (of that brand) will produce an image of the same magnification at the sensor regardless of the sensor dimension. What changes is the area of the projected image, not its magnification.

So let’s look at how this works.

The set-up

A standard, single focal length 200mm prime telephoto lens is mounted on a tripod. A subject is placed at a constant, pre-measured distance from the lens for all images. And two camera bodies, Nikon D90 with its APS-C sensor and Nikon D800 with its full frame sensor, were used.

The Process

Two photos of a mounted scaled quail are made from the same spot. Nothing changes but the camera bodies. Both images are processed in Photoshop in the same manner. A new composite file was made using both images together. Each image was reproduced at the same magnification for comparison. The APS-C image is produced at a six times multiple of its actual size of 15.7 x 23.6 mm, and the full frame image is printed at the same six times multiple of its actual size of 24 x 36 mm.

The Result.

One can clearly see the subject is the same magnification on both sensors and the reproduction sizes of the bird are the same for both sensors. The full frame sensor on the left captures significant additional area than the smaller sensor. This is the source of the term “Crop Sensor”.

Crop-Full Comparison

Left: Full frame sensor, Nikon D800. Right: Nikon D90 APS-C sensor. Initial enlargement (left) = 6 times sensor length 36 mm x 6= 216 mm. Initial enlargement (right) = 6 times sensor length 23.6 mm x 6= 141.6 mm.

The Misconception

When both images are reproduced at the same dimensions, the APS-C subject is reproduced at a larger size. This is only because the image is blown up to be the same reproduction size. This is why some people think there is actual in-camera magnification increase.

When viewed in the camera through the viewfinder or in live-view the smaller sensor frame is filled with the subject at a given distance than the full frame sensor. Therefore, the APS-C camera appears to produce a larger image. This is simply because the frame is filled faster with any given focal length and subject distance. What actually happens here is that the APS-C (crop sensor) image is blown up to match the outer dimensions of the full frame image.

Same enlargement comparison

Left, Nikon D800 full frame sensor. Right, Nikon D90 APS-C sensor.

Image quality

Image quality is not entirely based upon image size at the sensor, but is based upon in-camera processing technology, pixel size and pixel density. Many “crop sensor” cameras have better sensors and processing engines than full frame cameras. But that’s another story. (Maybe later.)

Copyright © 2014 Brian K Loflin . All rights reserved.