|
January 2005VOLUME 3 NUMBER 1 |
Looking at Lenses Pt. ILOOKING at LENSESPart I in a Series The Controversial Lens Factor Examined Digital Single Lens Reflex (DSLR) cameras are currently shipping with three different sensor (the light capturing unit, which replaces standard film) format sizes. The first is the full-frame 35 mm size sensor, which measures in at 24 mm tall by 36 mm wide. The digital sensor is the same size as a standard 35 mm film frame would be and have an 11 to 16 Mega Pixel (MP) count. The second sensor size is referred to as the APS, APS-C, or Compact sensor. The sensor is approximately 15 mm x 22 mm, which is near the same size as the old APS film frame size. These sensors contain 5 to 11 MP. The third size sensor is referred to as the 4/3 (four/thirds) sensor, which is an open standard currently only being used by Olympus DSLR cameras. For more information about digital camera sensors and why point and shoot cameras pixel sizes are not the same as DSLR pixel sizes, please see picturelinenews September 2004 here: http://www.pictureline.com/newsletter/2004/september/pixels.html Despite these different formats currently in use, most DSLR’s continue to use the same lenses as their 35 mm film counterparts, essentially because there are millions of existing lenses already in the field. However, when the sensor format is smaller sized than full-frame 35 mm, the effective subject magnification of the lens intended for 35 mm is changed. A normal lens is considered to be one that sees the world with a similar perspective to our eyes when looking at a subject from a moderate distance. For the 35 mm format a 50 mm lens is deemed normal. For the 2 1/4 “, square format, 80 mm is normal, 6x7 cm uses 105 mm as normal and 4x5 “ format uses 150 mm as normal. The focal length of a lens never changes, but the magnification of the subject within the format does change. For example, if we took a normal 150 mm lens from a 4x5 inch format camera and put it on a 35 mm (1x1.5 inch) format camera it would become a medium length telephoto due to the increased subject magnification. The lens itself did not change, but its usage on a smaller format provided greater enlargement over the smaller format. The same thing would happen if we took a 75 mm lens, which would be a short telephoto on 35 mm, but a very wide angle on 4x5” format. This intensification is what is happening with smaller format DSLR cameras. The smaller sensors are receiving greater magnification from the full-frame size intended lenses. Therefore digital camera users are seeing a new set of numbers appearing in their camera literature labeled as the “Magnification Factor, Multiplication Factor or Lens Factor”. The smaller sensors experience a 1.5 to 1.7x magnification boost (2x in the case of Olympus) which needs to be addressed by the camera / lens user. In the case of Nikon, with a 1.5x factor, each 35 mm size lens must be multiplied by 1.5 to determine the correct perspective for their smaller sensor size. A normal 50 mm x 1.5 equals an effective 75 mm lens. For Canon multiply by 1.6 (50x1.6=80).  DSLR users will continue to see the “Factor” used in their camera literature, because the photographic industry has decided to use that convention of explaining lenses in terms of the 35 mm format, at least for now. As you can see this is all great news for anyone who makes photographs primarily with telephoto lenses. You can now get the effect of a long, expensive telephoto lens used for 35 mm cameras with a much smaller, less expensive lens. For example, you can purchase a high-quality 200 mm f/2.8 lens for around $750.00 and use it on a smaller format DSLR camera. The 200 mm x 1.6 factor = 320 mm f/2.8 lens in use for a fraction of a 300 mm f2.8 lens costing around $4200.00. You now have a smaller, lighter lens costing one-quarter the price. Another benefit is since the sensor is smaller it is using only the central portion of the optics, which are always the prime, sharpest part of the lens. On the downside, this effect does limit wide-angle choices. A wide 24 mm lens may only act like a moderately wide 35 mm lens on a small format sensor. And the thought of purchasing an expensive wide 17 – 35 mm zoom for $1600.00 and having react only like a moderate 28 – 56 mm lens, leaves one baffled and upset. Finally the camera manufacturers have come to our aid. They have begun building a new set of lenses designed specifically for the small sensor cameras. Nikon labels their offerings with a “DX” designation and Canon with the “EF-S” label. Other independent lens makers have specially designated lens offerings as well. In the case of the Canon EF-S lens, the mount is sufficiently different as to prevent their use on a non-intended camera. With other lens / camera combinations some caution must be exercised to avoid using a small sensor lens on a large sensor camera or a film camera. If the lens is inadvertently used on the wrong type of camera, severe vignetting will occur. On the up side the user will immediately see the darkened edges in the viewfinder. Nikon currently offers a 10.5mm f/2.8 DX Fisheye, a 12-24mm f/4 DX zoom, a 17-55mm f/2.8 DX zoom, and an 18-70mm f/3.5-4.5 DX zoom. Canon currently offers an EF-S 10-22 mm zoom, an EF-S 17-85 mm IS zoom lens, and an EF-S 18-55 mm zoom. As you will notice, all of these lenses are all designed to fill the wide-angle gap. The following table may help with the conversion factors: Canon Lens – with a 1.6 x lens factor
Nikon Lens - with a 1.5 x lens factor
Order your lenses from pictureline here: http://www.pictureline.com/photographic/lenses/index.html All the best from your friends at pictureline. |
Digital U
Product Reviews Book Tip of the Month |
|
About Pictureline
|
Customer Reviews
|
|
© pictureline.com 2010 305 West 700 South • SLC, UT • 84101 |