teleconverter and exposure : LUSENET : Konica 35mm SLRs : One Thread

How to set exposure manually when using a 2x teleconverter?

I have a kiron 2x, and I am thinking to use it with a 200mmf3.5 Hexanon on my FS-1.

Suppose the correct exposure under a particular light situation is f16 and 1/125. Should I set the aperture on the 200mmf3.5 at f8?

Do I need to take off the 2x converter to meter correctly, in another words, under above mentioned light situation, will I see the f16 LED lights up when I have the 2x converter on?

Thanks! Wenbiao

-- Anonymous, November 03, 2000


Re: Teleconverter and exposure

Suppose the correct exposure under a particular light situation is f/16 and 1/125 - assume that is the exposure indicated by both 1) a handheld meter, and 2) the camera's built-in meter without the teleconverter installed. Now mount the teleconverter on the camera. You should notice that the correct exposure indicated by the built in meter is now f/8 and 1/125 - two stops different! In your example - f/8 should be lit up, rather than f/16. This is because of the way the teleconverter functions. What the teleconverter essentially does is take the central portion of the image formed by the lens and "enlarges" it to cover the film plane. This means that a good portion of the light gathered by the lens is discarded (or lost) - it simply bounces around inside the teleconverter/lens. This is why a 2x teleconverter loses two f stops.

The built in meter is measuring this reduced light level, and suggests that you set the lens to f/8. But remember, the setting "f/8" on the lens is really an effective aperture of f/16 - the proper exposure for the scene. The teleconverter causes two metering effects that perfectly compensate each other and offset - it reduces the effective aperture of the lens by two f stops, and it introduces an metering "error" of two f stops at the same time.

In summary, with a teleconverter mounted you should set exposure as follows:

AE or EE exposure - set the lens to AE and the teleconverter to AE. The built in meter will set the proper aperture for perfect exposure.

Manual exposure using the built in meter - Take the lens off AE and set the teleconverter to M. Set the f/stop on the lens using the built in meter as a guide. In other words - meter the scene (let's say f/8 at 1/125) and then set that value on the lens. If you switched to manual because you wanted to overexpose by one stop, for example, you would set f/5.6 on the lens.

Manual exposure using external (hand-held) meter - Take the lens off AE and set the teleconverter to M. Meter the scene using the hand-held meter. Adjust the exposure suggested by the meter by two stops when setting the camera. In other words - meter the scene (let's say f/16 at 1/125) and then set the lens after adjusting the exposure by two stops (to f/8 at 1/125). You could, of course, adjust shutter speed by two stops rather than aperture - the effect will be the same - proper exposure.

-- Anonymous, November 07, 2000


Thanks, Gerald! This is exactly what I wanted to know.

However, I think my 2x is having problems, when I meter without the 2x I get, say f16 and 1/125, then if I put on the 2x and meter the same subject, I got f2 and 1/125! So, I will meter without the 2x and then put 2x on to take pictures.

-- Anonymous, November 10, 2000

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