No Open Iris In Wide-Photo? at DVinfo.net

Aviv Hallale · April 21st, 2007, 05:44 PM

I was shooting a band today, one shot was in telephoto with the iris open and a gain of 3db. When I moved to widephoto, I noticed the iris automatically went down to F2, but the 3db was still displayed. However, in widephoto, I could manually open the iris again. The adjustments were on manual, autolock in the middle position.

I understand that this isn't a defect, but what is the principle behind closing the lens during a wideshot? Is it to deepen the depth of field?

Bob Hart · April 21st, 2007, 09:20 PM

This is a normal optical characteristic of some zoom lenses. Other zoom lenses are designed to perform with the same aperture value through the whole zoom range.

Tom Hardwick · May 14th, 2007, 03:12 AM

It sounds to me Aviv that your shots at full telephoto were under-exposed by half a stop. You were shooting wide open (f/2.4) at +3dB of gain up? Then you pulled back to wide-angle and the camera chose f/2 at the same gain setting?

That would suggest to me that it wanted f/2 in the first place, and your zoom isn't that fast at the 72 mm end. It's nothing at all to do with D of F and all to do with the fact that the max aperture of your zoom varies from f/1.6 to f/2.4 depending on what focal length you're shooting at. All perfectly normal.

tom.

April 21st, 2007, 05:44 PM	#1
Aviv Hallale Major Player Join Date: Mar 2004 Location: Cape Town, South Africa Posts: 276	No Open Iris In Wide-Photo? I was shooting a band today, one shot was in telephoto with the iris open and a gain of 3db. When I moved to widephoto, I noticed the iris automatically went down to F2, but the 3db was still displayed. However, in widephoto, I could manually open the iris again. The adjustments were on manual, autolock in the middle position. I understand that this isn't a defect, but what is the principle behind closing the lens during a wideshot? Is it to deepen the depth of field?

April 21st, 2007, 09:20 PM	#2
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,477	This is a normal optical characteristic of some zoom lenses. Other zoom lenses are designed to perform with the same aperture value through the whole zoom range.

May 14th, 2007, 03:12 AM	#3
Tom Hardwick Inner Circle Join Date: Mar 2003 Location: Billericay, England UK Posts: 4,711	It sounds to me Aviv that your shots at full telephoto were under-exposed by half a stop. You were shooting wide open (f/2.4) at +3dB of gain up? Then you pulled back to wide-angle and the camera chose f/2 at the same gain setting? That would suggest to me that it wanted f/2 in the first place, and your zoom isn't that fast at the 72 mm end. It's nothing at all to do with D of F and all to do with the fact that the max aperture of your zoom varies from f/1.6 to f/2.4 depending on what focal length you're shooting at. All perfectly normal. tom.