Lens The fast telephoto

[Charzes44]

Not a zoom. Variable focal length.

What's the difference Brian?

 

[Brian]

What's the difference Brian?

A zoom lens maintains focus when changing focal length. This is done with multiple groups moving to keep the back-focus of the image constant as the focal length changes. Most zoom lenses these days are variable aperture, simplifies the design. Constant aperture zooms tend to be big.
The Variable-Focal length does not do this- trades that convenience to provide a fast aperture, constant F2.8. But- means manually correcting the focus.
The ultimate cult Series I.

 

[Charzes44]

A zoom lens maintains focus when changing focal length. This is done with multiple groups moving to keep the back-focus of the image constant as the focal length changes. Most zoom lenses these days are variable aperture, simplifies the design. Constant aperture zooms tend to be big.
The Variable-Focal length does not do this- trades that convenience to provide a fast aperture, constant F2.8. But- means manually correcting the focus.
The ultimate cult Series I.

Yes, I see. Thank you.

 

[2SHOES]

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[mnhoj]

Fuji 56mm F1.2WR

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[mnhoj]

Viltrox 75mm F1.2

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[ac12]

What's the difference Brian?

Back in the film days . . .

The practical effect was as Brian said, a zoom will maintain focus as you zoom, where as a VFL you would have to refocus as you change the FL.
This was not really an issue with single-ring zooms (push/pull to zoom, rotate to focus), as your hand could do both at the same time.
But with a TWO-ring zoom, you had to move your hand from the zoom ring to the focus ring, to refocus the lens.

But today, with autofocus, it isn't the issue that it used to be in the manual focus day. The camera keeps the lens in focus.