ABOUT TRIPOD, HEAD AND VIBRATION
The reason I start this chapter with the word ‘res- olution’ is simple, to set the maximum allowable level of vibration. In fact, dealing with all the physics of ray or light is beyond the level of this article. However, you are asked to accept the general idea that the light rays on film is not a point but a circular shape, i.e. donut. Erwin Puts mentioned that the minimum donut size is about 0.005mm in diameter.10
when all the effects like film flatness, focusing accuracy and other effects are included. 12 Re- cent digital SLR has another problem of its own. They generate more heat which can deform the internal body structure causing thermal defor- mation error.
Practical maximum resolution is about 20~25um if the whole system is taken account.
We are dealing with hot donuts of 0.005mm in diameter.
According to the article on EETIMES13
in 1999, Fuji
Super CCD is known to have 4.5um pitch be- tween pixels. And currently it is about a few mi- crons. And with some exceptions, image sensor has multiple color channels in planar orientation. So it becomes obvious that the vibration is more dangerous in digital camera. If we regard the vibration as a sharpness killer, the 135 format dig- ital SLR is the easiest target.
So we are dealing with 5um donuts, baked hot, ready to leave traces on the film or sensor. And if there are vibrations, all the sweet coverings on donuts will scatter. If you want a tasty donut, try not to vibrate the donut while moving them.
A rigid support plays an even more important role in an era of digital imaging. Especially for the digital SLR camera you should use faster shutter speed and a stable support to make your huge investment worthwhile. Even the VR, IS or AS lens14 can perform at its best when provided with a stable support. Once you know the speci- fications and price of commercially available MEMS gyro sensor, you can understand the limit of these kind of vibration reduction system.
Images of light are finally captured on film or sensor. And we enjoy the picture in various for- mats like print, projection, CRT monitor, LCD, etc. So what is the determining number in terms of final media of image?
Testing a tripod system was more complicated experiments than I first imagined. It is not simple because there are too many parameters affect-
We can find a good and well organized data at Norman Koran’s web page. 11 Practical limit of resolution is often mentioned to be 20~25um
10 See the document named ‘Leica R-lenses’ in official Leica homepage. http://www.normankoren.com/Tutorials/MTF7.html 11
12 Robert Monaghan at Medium format club http://medfmt.8k.com/mf/limits.html
13 14 http://www.eetimes.com/story/OEG19991020S0073 VR (Vibration Reduction), IS (Image Stabilizer), AS (Anti Shake). Whatever the name is, they all based on miniature gyroscope sensor readout that tells how much it vibrates in rotational direction.
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ing the level of vibration and these are also in- terconnected. It is so small to be measured by general measuring tools.
In the field, all these parameters are responsible for the final result. But to understand the nature of camera vibration, parameters have to be mi- nimized. It took me most of the time to get to know the typical working range and error mar- gin of various parameters.
Here some sample parameters are listed.
where the tripod stands
the method or material used on each leg's foot
center pole or direct attachment
base attachment of tripod head
ball or 3 way head itself
quick shoe or bolt mount
fixing of camera plate and camera
Lens mount, shutter, mirror, body struc- ture, body weight, etc.
Performance of the system is defined by the weakest part or the joint. If you are a long time car owner, you would understand what I mean. I can’t remember the exact sentence but a copy like “90% of the Camry still on the road since first launched” which claims a quite similar situation. It means it is well balanced product with lesser or no weak point. When one is to live with some- thing or someone for long time, having less weak points is better than having a few wonderful as- pects with more weak points. At least, it is my belief in selecting or designing a product.
However, let me throw a spell to better under-