How "bright" is your lens?

C

Colin Barratt

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I just bought a 15-30mm Sigma for my D100. I compared it with my 24-85mm Nikon f3.5 - 4.5 and the results for the Nikon were 1.5 stops darker when at identical settings. Why do you think this is?

Colin
 
Colin Barratt said:
I just bought a 15-30mm Sigma for my D100. I compared it with my 24-85mm Nikon f3.5 - 4.5 and the results for the Nikon were 1.5 stops darker when at identical settings. Why do you think this is?

Colin
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I could only guess that the 14-30 is a DC lens? If so it is designed for short focus whereas (I assume) the Nikon is not. Additionally, you're gathering more ambient light from a scene with your wide(r) angle.
 
What is the f rating of the 15-30?
 
The 15-30mm is a 3.5 - 4.5 as well. The full aperture shouldn't affect the brightness of the final image, only the viewfinder image. I have always had to add 1 - 1.5 stops with the Nikon lens because it generally gives darker images than I like and is at its best in bright situations. The 15 - 30mm is a DG lens so it is designed to cover a full frame and would deliver as much light to the sensor as the Nikon. I agree that the wide angle lens collects light from a wider area but the result on the final image should be the same. If that was not the case telephotos would be very very dim whilst wideangles would be ever so bright !

Colin.
 
Don't think you will know unless you can compare to another identical lens. Either lens could be malfunctioning as to how much it closes the iris?
 
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