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Why won't my lens step down to its maximum aperture?

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BP2324
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Location: Theydon Bois, Essex

Why won't my lens step down to its maximum aperture?

Post by BP2324 » Sat May 01, 2021 5:27 pm

My Sigma 120-400 on both my bodies Nikon D7500 and D50 will only step down to F5 (should be F4.5) at 120 focal length, and at 400 I only get F6.3 (should be F5.6)
I have tried Manual and Aperture modes and both well lit and darker scenes with low and high ISO settings.

My other lenses both Nikon do reach their maximum aperture on both bodies, so I'm leaning to thinking this is a problem on my Sigma lens. If so what problem?

Answers on a post card please as they say.
Thank you for taking the time to read and hopefully replying.
Brian

EGVP
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Re: Why won't my lens step down to its maximum aperture?

Post by EGVP » Sat May 01, 2021 5:48 pm

Have you cleaned the contacts on the lens?
I should probably change my name to EGCC again.

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reaper493
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Re: Why won't my lens step down to its maximum aperture?

Post by reaper493 » Sat May 01, 2021 9:16 pm

I think, it could potentially be to do with the distance you are trying to focus at.
I seem to remember something a colleague told me many moons ago when I sold cameras/lenses in a well known retailer, where some lenses will not allow the maximum aperture to be used when focusing on infinity, or at the longer reaches of the lens. I experienced it on my sigma 170-500 with a D70/D200.

Does it let you open it up when focusing on closer objects?

Mike

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