Where To Find Katydid

SMC Pentax-A 28mm f:2.8

Although I tend more toward the telephoto Avoi some great angles do peuit not hurt. I came across this little 28mm by chance on the bay. Not too expensive, and more SMC Pentax-A, non-M, which does not spoil anything.

• Type: fixed lens, manual focus and iris automated
• Manufacturer: Pentax
• Model: SMC Pentax-A 28mm f: 2.8
• Purchase Date: September 27, 2007
• filter holder: 49mm
• Aperture: f/2.8 to 22, five blades
• Focus: 30cm to infinity

So why A ? That's automatic simply: the diaphragm of the lens can be set directly by the housing, without user intervention. If the box has a program mode, it will even automatically adjust the aperture and shutter speed, depending on available light and sound or its programs.

Specifically, what's the difference? Unlike the F-Pentax lenses, there is no integrated electronics, and mechanical couplings are very close to those goals Pentax-M. But not quite ...

First, there are a number of electrical contacts that allow the case to know the characteristics of the target. Objective side, in fact, there is not actually contact the contrary, a small plastic pellet is at the location of some of the switches used for housing insulation, for others, contact is established by the metal frame. These contacts or absence of contact can encode openings maximum and minimum diaphragm history that the case does not ask the impossible.

An additional contact is a bit unusual, distinguished on the fourth picture, roughly halfway between the two screws on the frame. It corresponds to the A position marked on the aperture ring (see third picture) and when this position is chosen, this little metal point juts slightly, making contact which means the case that one wishes to use the auto iris. Note that if the case does not use these contacts, the target behaves almost as an objective of the series Mr.

A more subtle differences: all mount lenses K have two mechanical couplers. One relays in case the position of the aperture ring and the second blocks the diaphragm in the open position to develop and adjust speed and aperture while keeping the lens wide open, which is much more convenient . Simply, the case made its claculs taking into account the width of the diaphragm when it is closed, information provided by the first coupler; when it starts shooting, the second coupler recedes, leaving the diaphragm closed.

On the objectives of series A, the second coupler is slightly modified its mode of action is more precise and carefully calibrated (the small bitonnieau metal visible on the top of the frame on the fourth photo). Result: while for the goals of K-series or M, his action was an all or nothing (keep the iris open, or back completely so that it closes at the selected position on the ring), with the objectives A, the case can not roll back the coupler only partially, leaving the diaphragm close, but only chosen by opening the housing. This is how the opening is chosen.

course, on my boxes ME Super or MX, it makes me look good: these packages do not have the ability to control the diaphragm and a M series lens would have given exactly the same result . For cons, the P30T (which I am separated from) the MZ-10 MZ- and 5n have this capability, and the Pentax digital SLR cameras as well, which is seriously taken up the series lenses A!