Telephoto shooting & Exposure at DVinfo.net

James Emory · November 4th, 2004, 08:57 AM

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.

November 4th, 2004, 08:57 AM	#1
James Emory Regular Crew Join Date: Aug 2002 Location: Atlanta, Georgia Posts: 1,892	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?

November 4th, 2004, 09:06 AM	#2
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	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. __________________ Jeff Donald Carpe Diem Search DVinfo.net for quick answers \| Where to Buy? From the best in the business: DVinfo.net sponsors

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November 5th, 2004, 10:38 AM	#3
Tom Hardwick Inner Circle Join Date: Mar 2003 Location: Billericay, England UK Posts: 4,711	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.