>>A normal SLR's TTL metering won't be any good for pinhole photography >>sincethere's no aperture size feedback to the camera's exposure circuit. A >>normal lens' aperture ring operates the camera's diaphragm resistor to >>tell the meter what aperture you've selected. With pinhole photography, there will >be no such connection. Metering will be via hand held meter or >>Sunny 16 (Moony 11) and aperture will be calculated. >> Scott Nelson wrote:
>Actually not true. On M and K series lenses, the lens tells the body how >many stops down from wide open the aperture is set using the mechanical >aperture coupler. These lenses do not communicate the absolute aperture. >If there is not such coupler on the lens, the body just reads it as wide >open (which is the correct exposure, because there is no auto aperture on a >pinhole). After all, most Pentax bodies still work with screwmount lenses >(no aperture info) and mirror lenses (also no aperture info, because it is >fixed). The more important issue is whether the TTL meter is sensitive >enough to give an accurate exposure with so little light. > Try this: Take a Pentax K body set on auto exposure, and a lens set at full aperture. Slowly twist the lens off the camera while looking through the viewfinder. You should find that although the image brightness stays the same, the calculated exposure will increase as you twist. In other words, without a lens or other object to turn the aperture coupling lever fully clockwise, the camera will calculate the exposure assuming the lens will stop down when the shutter is pressed, when for a pinhole, etc. this won't be the case. Therefore (if not using an LX), for getting correctly exposed photos for pinholes, microscopes, etc., you need to make sure the aperture lever is locked at maximum - a T2 mount or M42-to-PK mount both move the aperture coupler and ensure this is the case. David Dixon - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
