Introduction

Camera exposure shutters with apertures in excess of 100 mm are hard to find on the "market". They are practically unavailable if very short exposure times (< 0.1 seconds) and/or photometric performance is required. Typical problems with common iris-type shutters are exposure time errors of several 10 msec and exposure non-uniformities of the same order of magnitude.

We have been confronted with these questions during the development of BUSCA, a 64 Megapixel camera for simultaneous imaging at four wavelengths [1,2]. A shutter was required with an aperture of 110 mm*110 mm that could provide very short exposure times <10 ms and exposure non-homogeneities of no more than 1 msec (i.e. < 0.1% at 1 sec).

Our initial designs were influenced by typical misconceptions about exposure shutters, for example,: i) a shutter is a mechanical device, ii) short exposures need very fast operations or movements, iii) only movements with highly constant speed guarantee uniform exposures, iv) because of these, lifetime and MTBF are real issues. Thus we made a few deviations before arriving at the relatively simple design that is now characteristic of Bonn Shutters [1,3]:

• The shutter system combines precision mechanics, micro controller based electronics and firmware for movement and overall control.

• Short exposure times and exposure homogeneity are achieved by precise control of the movement of two independent blades. The acceleration phase can even take place in the shutter aperture.

• These blades run impact-free on industry quality linear ball bearings. There is no contact between the blades and the bearings. Constant performance over several million operations can be expected.

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