Super Hoods and Sweet Spots

Written by Steve Sint
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Published on January 12, 2003
TAGS: adorama
Steve Sint
Adorama ALC

Just as we’re starting to see, full-frame, 35mm sized sensors on digital cameras (such as the Canon EOS 1Ds), I’m beginning to think that smaller, APS-sized sensors, found in most Digital SLRs, are the way to go. Since July, beginning with my acquisition of a Nikon D100, I have shot about a dozen magazine articles using it and I have not exposed one frame of film!

Although all of these smaller chip, “multiplier” cameras suffer when compared to the wide-angle capabilities of full-frame digital and film 35s, there are unique features that these bring to the table.

Soon after getting my hands on my D100, I purchased a lens that I thought I would never have to buy again: a 50mm f/1.4. Factoring in the D100’s 1.5X 35mm lens factor, this lightweight, small filtered, lens offers the perspective of a 75mm f/1.4 lens. That’s perfect for intimate portraits, yet the lens is 1/4 the price of Nikon’s 85mm f/1.4 lens, which accomplishes basically the same thing on a full-frame camera.

But there is more to this story. The lens is much lighter; it accepts smaller filters (like 52mm instead of 77mm!); and then there’s the lens hood. As a crafty view-camera photographer, I realized a lens designed to cover a 24x36mm frame (or sensor) has much more “coverage” than I need to cover a 15x24mm APS-type sensor! If less if a lens hood causes vignetting on the 24×3 mm frame, no problem, as long as it doesn’t vignette on a smaller sensor.

After some experimenting, I chose a lens hood from an ancient 105 mm, f 2.5 Nikkor to use over my 50mm lens. Although this will cause vignetting on a full frame 35, it doesn’t on the D100. Likewise, my 24mm f/2.8 Nikkor sports a lens hood I stole off my 85mm f/1.8 Nikkor; there’s no trace of vignette woes!

Another discovery

Because the sensor on the multiplier cameras only sees the central part of the lens’ circular projected pattern (a “sweet spot”), I discovered that lenses that I might avoid due to poor edge performance on a full frame 35mm camera became worthy of a second look. A lens that poorly resolves details at the edge of full-frame 35mm just might have central optical performance good enough to become very interesting on a small-sensor SLR.

Case in point: the Tamron 80-210mm f/4.5-5.6 (120-300mm 35mm equivalent). While it certainly isn’t up to the optical quality or speed of my 80-200mm, f/2.8 AFS Nikkor (especially wide open and/or at the edge of the full 35mm format), the fact that it weighs 9.1 oz (compared to the 60 oz. 2.8 Nikkor), and costs $ 95 (about one-fourteenth what the AFS f/2.8 does!) is tantalizing. The fact that it accepts only 52mm filters (compared to 77mm filters on the AFS f/2.) makes it even more so. And, digital’s ability to pump up the ISO when needed makes it a very enticing, lightweight, package!

This is not meant to belittle the 80–200mm Nikkor. That lens offers the perspective of 120-300mm on the D100. With the addition of the 1.4X Nikon tele-converter, it becomes a very reasonably priced autofocus 420mm f/4 telephoto on the long end!

Lastly, I used to carry a macro lens as part of my kit. Close-up lenses offer poor edge performance, and I passed them over for use on full-frame 35mm SLRs. But on small-sensor DSLRs, these same faulty filters provide very acceptable optical performance in the center of the image. Every one of my lenses is now capable of close-up work on a small-sensor DSLR. A few filters can replace a prime macro lens with little or no loss of image quality.

Now that Nikon has announced a new 12-24mm zoom (18-36mm full-frame equivalent), designed exclusively for their digital cameras, the wide-angle side of things is finally becoming workable! This digital-only lens, combined with the oversized lens hoods, sweet spot lens performance, and close-up lens capability when using traditional, full frame lenses on the small sensor breed of digital SLR are adding fuel to the digital revolution.

Considering these added benefits, and the relatively low price of the small sensor digital SLR’s when compared to some of the newest full frame digital SLR’s, these cameras are becoming more attractive every day.