Canon manual 47

Not For Resale – Free Download at http://www.joe-chan.com/manuals

Metering at Low Light Levels

With AE coupling all the way down to EV -2 (with ASA 100 film), the A-1 is capable of metering and producing a natural rendition of the light in very dim lighting conditions. Since EV -2 is practically the lowest light level at which you can even perceive your subject through the viewfinder, you can basically perform AE photography with the A-1 as long as you can see your subject in the viewfinder when using a film with appropriate sensitivity. This means that the A-1 will usually give you a meter reading even in the most adverse of lighting conditions when performing photomacrography and photo- micrography in the stopped-down AE mode.

What this also means is that you will be using very slow shutter speeds and may be subject to failure of the reciprocity law. The reciprocity law is that relationship between apertures and shutter speeds discussed earlier in which several combinations of the two will give the same exposure value. The trouble with this law is that it may not hold true at slow shutter speeds. More exposure may be necessary. You will find information concerning reciprocity law failure and how to correct it in the data sheet that comes with your film. Correction of reciprocity failure may involve increasing the light

level so that higher shutter speeds can be used. Even when following the instructions of the film data sheet, it is advisable to slightly adjust the exposure over several shots to get at least one perfectly exposed image.

Be especially on the alert for reciprocity failure when using color reversal (slide) film which has a smaller exposure latitude than black and white or color negative film. Having a smaller exposure latitude means that it is more touchy about exposure error. Incorrect exposure by only 1/2 exposure step may make a noticeable difference in the image results. Reciprocity failure with color film will result in color shifts as well as underexposure and may require corrective filtration as recommended by the film manu- facturer.

–47–