To πρόβλημα της σκόνης στις D-SLR μηχανές: Οι περισσότεροι κάτοχοι ψηφιακών μηχανών SLR είναι ενθουσιασμένοι από τις εκπληκτικές φωτογραφίες και τον ποιοτικό εξοπλισμό που απολαμβάνουν. Το σύστημα της μηχανής που κατέχουν αντιπροσωπεύει μια επένδυση με διάρκεια ετών. Υπάρχει η περίπτωση να εκπλαγούν από μια λεπτομέρεια. Η ανακάλυψη μικρών και μαύρων σημείων στις φωτογραφίες τους αποτελεί την εμφάνιση σκόνης στον αισθητήρα εικόνας.Σε κάθε αλλαγή φακών υπάρχει η πιθανότητα η σκόνη να εισχωρήσει στη μηχανή. Ακόμη και αν προσέξετε πολύ κατά την αλλαγή, τα μηχανικά μέρη όπως το κλείστρο ή ο ταχείας επαναφοράς καθρέπτης μπορεί να κολλήσουν σκόνη κατά την κίνησή τους. Συγχρόνως ο αέρας που δημιουργούν μπορεί να μεταφέρει τα σωματίδια εσωτερικά στη μηχανή. Αυτό δεν είναι τόσο σημαντικό στις SLR με φίλμ διότι η σκόνη εξαφανίζεται στην αναδίπλωση του φίλμ. Στις ψηφιακές μηχανές όμως, ο αισθητήρας παραμένει σταθερός στην ίδια θέση. Ακόμα και με τα σωματίδια σκόνης μεγέθους 0.1mm(100microns) και ουσιαστικά αόρατα στο ανθρώπινο μάτι, από τη στιγμή που θα επικαθίσουν στον αισθητήρα εικόνας θα μειώνουν την ποιότητα των φωτογραφιών κάθε φορά που θα φωτογραφίζετε. Τέλος, είναι αρκετά δύσκολο να καθαρίσετε τη σκόνη και θα χρειαστεί να στείλετε τη μηχανή για σέρβις.
Olympus is the pioneer of dust-free D-SLR photography. It was the first manufacturer to face this annoying problem by developing a unique and innovative solution to defeat it – the Supersonic Wave Filter (SSWF). It forms the main part of the Dust Reduction System, the one that keeps the image sensor free from contaminants. This system was introduced together with Olympus’ first digital SLR, the E-1 in 2003, and has been incorporated to wide acclaim in all seven Olympus D-SLRs since. Recently, the dust reduction system was perfected even further. Now, this second generation SSWF is even more effective. To accommodate the greater need for dust removal due to the higher pixel density of 10 Megapixel image sensors, the vibration frequency of the SSWF was increased and the main frame reinforced. At the same time, the size of the system is reduced leading to a decrease in the volume of parts around the mount box, allowing further size reductions in camera bodies. Now some other manufacturers are beginning to recognise the problem and are incorporating dust protection systems in their models. However, Olympus remains the initiator of dust-free D-SLR photography and is the only manufacturer with a proven track record in eliminating the problem of dust.
Two types of dust There are two main types of dust that have the potential to damage photos: Dust particles that adhere through electric force and dust particles that adhere through intermolecular force.
(1) Dust particles adhering through electrostatic charges Most of the contamination to be found on the image sensor surface is caused by dust particles as small as just one micron (0.001mm) adhering to it through electrical charges. By examining dust particles and the surface of the Supersonic Wave Filter under a microscope, it was discovered that the particles themselves have electricity and carry a positive electric charge, while the image sensor is negatively charged. This makes them gravitate to each other. The same phenomenon can be observed on the surface of LCD and CRT monitor screens. This type of dust can easily be removed by the SSWF.
(2) Dust particles adhering through intermolecular force
The intermolecular force is weaker than electrostatic charges. However, it still attracts microscopic-sized dust to the image sensor even with infinitesimal force. While earthing the camera can help reduce the problem of static dust it does not avoid intermolecular attraction. But the ultrasonic vibrations of the SSWF can solve this problem. If dust or flour is drizzled into the camera, it still adheres to the surface of earthed metal. This kind of dust is attracted by intermolecular force. Liquid also adheres to the image sensor by intermolecular force and such molecules adhere strongly due to their ability to get closer to the adhesion surface, making it harder for dust reduction systems to remove the dust completely. In such instances, wiping the optical element, such as the Low Pass and Infrared filters, in front of the image sensor with cleaning fluid is effective. However, there is little or no possibility of liquid adhesion to the SSWF during regular use.
The SSWF is automatically activated every time the camera is turned on, generating ultrasonic vibrations at more than 35,000 times per second or more, that shake off dust on its surface. It can also be invoked manually via the camera menu. The removed dust is then captured on an adhesive absorber at the bottom of the filter. In most instances, its operation is generally indicated by the blinking of a blue LED on the top of the Olympus camera body.
(1) Ultrasonic dust removal Through the ultrasonic vibrations, any dust particles that have adhered to the surface of the SSWF are instantly removed. They are then captured on an adhesive dust absorber at the bottom of the filter. The material used for the filter was very carefully chosen, as it needed to be free from any kind of reflection. The SSWF consists of a discoid plate and a piezoelectric element.
(2) Preventing dust from reaching the image sensor The Dust Reduction System prevents dust from settling on the image sensor by hermetically sealing the space between the SSWF and the image sensor surface. This is achieved by applying a special rubber seal between the image sensor and Low Pass Filter as well as the Low Pass Filter and SSWF.
(3) Preventing dust from appearing in the image Due to the space between the sensor surface and the SSWF, dust is not projected clearly therefore it does not block the light and won’t appear in the image. In addition, the SSWF is hermetically shielded by a rubber seal so the ultrasonic vibrations do not affect other components. Applying a frequency voltage of more than 35kHz to the piezoelectric element activates the resonant vibrations of the SSWF. The vibrations are flexed vibrations, making it possible to effectively eliminate dust from the SSWF. The mechanism of the E-System’s resonant vibrations is the most efficient way of generating an amplitude of ultrasonic vibrations for eliminating dust particles.
