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-   -   Telephoto shooting & Exposure (https://www.dvinfo.net/forum/sony-vx2100-pd170-pdx10-companion/34454-telephoto-shooting-exposure.html)

James Emory November 4th, 2004 08:57 AM

Telephoto shooting & Exposure
 
I have a question about wide & telephoto shooting. I thought that when you shoot telephoto that you loose light and when you're wide you gain light, that is more than when telephoto. Is this correct? I was using a PD-150 with manual iris and had it wide open at 1.6 and totally wide. Then, when I zoomed in, the camera bumped it down to a 2.0. Why would it close the iris down when I needed more light when telephoto?

Jeff Donald November 4th, 2004 09:06 AM

The lens is a a variable aperture lens. The maximum aperture changes as you zoom the lens. The camera will automatically adjust the exposure as you zoom, assuming you are in an automatic mode. In manual, the scene will darken. Manufactures build variable aperture lenses due to cost considerations.

Tom Hardwick November 5th, 2004 10:38 AM

James - most supplementary lenses (wide-angle and telephoto converters) are three element assemblies. What happens if you film through three extra sheets of glass? Right - you lose some light.

Modern lens coatings are so good that the losses are small, but they're there nonetheless. The camera will automatically take these losses into consideration so no need to worry about it. But if it gets really dark, take them off.

On your PD150 maximum aperture at full wide-angle is f1.6, and on full telephoto you lose a stop, and max aperture is f2.4. This falloff is constant, so in the middle of the zoom it's f2. The lens has been designed like this to keep it compact, light and cheap-to-make-sharp. All domestic camcorders are built like this.

If it's dark - film at wide-angle.

tom.


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