A Short Summary - Digital Lenses
Monday, February 19, 2007
Happy Chinese New Year!
I spent some time reading Amateur Photography, which is a popular UK photographic magazine, and came across some information on lenses. If you happen not to know, there is a small war between "cropped"(C)-sensor camera and full-frame (FF) camera. It's mainly between Nikon, representing the C-sensor, and Canon, representing the FF-sensor. I am on the Nikon C-sensor side. It's not that I am using a Nikon camera that I am saying this. But rather, C-sensor cameras are cheaper and that suits a student's budget. Also, one doesn't need such a good lens to get quality image on a C-sensor; money-saving again! For explanation, read on...
Content Summarized from the following articles (Amatuer Photographer 28 October 2006)
- APAnswers by Barney Britton
- Tamron AF 17-50mm f2.8 XR Di II LD Asph (IF) Review by Geoffrey Crawley
A vintage Nikkor lens might give excellent result on a film camera but not on a digital body. This is not because the lens is below par but it wasn't designed with the digital sensor in mind. Light can hit film from a wide range of angles, and as long as it's properly focused, the film will record a sharp image. In digital sensors, light need to strike as close as possible to 90 degrees or the resulting image can display chromatic aberrations or vignetting. The problem will be much more severe close to the edges of a full-frame digital SLR, but still can be a problem even on those with "cropped" sensor. With an older or cheaper lens, the image defect will get even more severe. Nikon's decision to stick to cropped-sensor DSLRs makes sense since the imaging circle is smaller. Therefore, the edges of the 35mm-format frame will not be shown. The logical design of Nikon's "DX" lenses is based strongly on this reasoning.
Based on the reasoning that photosensors require the minimization of extraneous light and the adoption of the telecentric principle, lenes were designed such that the emergent rays from a lens arrive more vertically at the sensor across its whole surface. In this way, the microlenses which are in front of the picture elements receive the light on the optical axes, giving minimum aberrations and vignetting. Also, any reflections from the sensor's polished surface return vertically and thus can be optimally minimized from the recomputed coating of the rear lens element's surfaces.
Ok, for a more boring article on lenses... refer to my previous post on MTF theory.
posted byWilliam at 9:25 PM
Labels: equipment, lenses, photography, technology
i've a sony cybershot T9 which takes blurry pics at night! thought i shld ask u abt it. hehe
Sony cybershot T9 is an extremely compact camera that has Sony Super SteadyShot optical image stabilization.
We will most likely have clear pix if we take with a shutter speed of 1/(focal length) of the lens zoom. So for example, T9 has a wide angle of 38mm and to take clear pixs, we can go to as slow as 1/38 sec shutter. But with the optical stabilization, maybe we can still have clear pixs at 1/10 sec shutter with the right techniques. But at this slow speed, make sure you stay as still as possible since the camera will also record your movement.
For night shots, for example Christmas light, a decent shutter speed at f3.5 ISO640 is 1/4 sec, which is more than most of us can handle clearly.
Here's some tips for increasing the chance of taking no-blur pixs without a tripod.
1)T9 has a maximum wide aperture of f3.5 at 38mm and a max CCD sensitivity of ISO640. Therefore, 38mm is the optimal lens zoom-length for hand-holding night shots (so try not to zoom when you want to take clearer night shots).
2)Brace yourself against something when you press the shutter. Squeeze the shutter s.l.o.w.l.y. Do not fast press.
3)The breathing pattern is important. Breath in, breath out half-way, hold your breath and squeeze.
4)The pinnacle technique of shutter release is to squeeze the shutter with the synchronization of heart-beat. We want to squeeze between heart-beat since heart-beat is able to vibrate the camera ever so slightly.
5)To take pple in a night shot, always switch on the flash to freeze the movement. So though the background might be blur, the pple in the foreground will be acceptably clear.
wow. thanks man. some more qns.. hehe
so which flash do i choose? the one that flashes once or the one that bursts into a few flashes?
f 3.5: are u talking abt the focus? so 3.5m?
I think the "few flashes" mode is the red-eye reduction mode. In theory, the few pre-flashes before the actual flash is to adapt the eyes to the bright (flash) light so that the eyes' irises become smaller. So when the flash hits the back of the retina , less of the red color of the body tissue will be recorded: red-eye reduction.
I almost never use this mode since many people will just close their eyes after the first flash and when the camera is actually taking the picture, you see only eye slits. Besides, this mode works poorly. You will still get red eyes if the technique is wrong. So, just use the single flash mode.
To prevent red-eyes, position the camera slightly above the eye-level (maybe even a slight tilt) so that the flash wouldn't hit the retina directly.
"f" number is use to indicate the size of the aperture. A bigger aperture will allow more light to come in a stipulated time than a smaller one. The smaller the number the bigger the aperture. T9 will set this for you so no fret.