What exactly is the advantage of constant aperture in a zoom lens?

Started Jan 20, 2013 | Discussions thread
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Simon Devlin
Simon Devlin Senior Member • Posts: 1,265
What exactly is the advantage of constant aperture in a zoom lens?

Hello,

I bought another Pentax-A 70-210 F4 zoom lens as the last one was a mushroom factory.

Anyhow besides the pretty good speed of f4@ 210mm I was wondering how to answer the question of the advantage of constant aperture throughout the zoom range, especially on an automatic exposure lens where my K-30 will quickly adjust the shutter speed or ISO to compensate. Have I answered my own question?

I suppose F4 throughout is also useful for blurring out more of the background.

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Simon
Legacy lens lover

Pentax K-30
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