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SL lens 90-280, Parfocal?


Sully
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As it is AF ....... does it really matter ....... particularly as AF is lightning quick ? 

 

It's often an issue for video users....although this is a long lens for that purpose.  The same question was asked regarding the 24-90....  http://www.l-camera-forum.com/topic/252213-sl-24-90-parfocal/

 

Jeff

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Maybe this is what is causing the production delays. It certainly ought to be parafocal. Older R zoom lenses were parafocal (or at least the Leica built ones were). This was more important on them than their Zeiss Contax competitors, as they were two ring (separate focus and zoom) action, against the single ring trombone focus/zoom action of the Zeiss, where it is easier to compensate for a non-parafocal lens. On the Contax zoom lenses, there were a series of adjustment screws under the rubber focus/zoom ring cover, to adjust the lens to be parafocal. This had to be done by an expert using an optical bench, as changing one screw altered the settings of the other screws. I would assume that the Leica R lenses had something similar. 

 

Wilson

Edited by wlaidlaw
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Why "ought" it to be parfocal? A parfocal lens was pretty important in the days of film and optical viewfinders, manual focus only, for still cameras as it aided focusing: zoom in, focus, zoom out, frame and shoot. But parfocal designs tend to be bulkier and heavier, and often sacrifice some resolution and contrast. Taking parfocal off the "must have" list allows lenses which perform a little better and are (maybe) a bit smaller and lighter. With AF being used 99% of the time by most users, the focusing advantage of parfocal lenses is generally no longer relevant. 

 

Lenses designed for video work tend to be parfocal, for the reasons others have stated. Although the SL makes a fine video camera, the SL lenses are primarily designed for still photography and the modern usage idiom—which is fast AF, AF-C with tracking, etc. biased. 

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I would welcome parfocal performance on the SL zooms if there were no other significant trade-offs.

 

That said, is there any reason the camera software could not recreate parfocal performance by measuring the focal length change along with a built-in lookup table for the focus behavior? This would be much faster than using the AF-C to check for focus again.

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Unfortunateley SL's AF very often is not fast, AF-C with tracking sometimes is very slow. So it matters when focus is lost.

 

That's not been my experience, but then I hardly ever use AF-C or Tracking. AF-S seems virtually instantaneous to me with the SL24-90 lens. 

 

(Of course, I most often use manual focus R lenses, so the whole question of AF speed is somewhat academic to me. I find it fast and easy to manually focus-track my subjects with a long lens, normally.) 

 

I would welcome parfocal performance on the SL zooms if there were no other significant trade-offs.

 

That said, is there any reason the camera software could not recreate parfocal performance by measuring the focal length change along with a built-in lookup table for the focus behavior? This would be much faster than using the AF-C to check for focus again.

 

 

Same here. 

 

Interesting idea. I don't know how feasible it might be, though. That would take a huge amount of precision from all aspects of the system. 

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I like par focal lenses. It's great with critical focus subjects being able to focus zoomed in and then zoom out to frame. However this becomes less of an issue with an EVF camera and focus magnification.

 

The big players in the mirrorless video market are Panasonic and Sony. Are any of their zooms parfocal? I know Sony makes at least one parfocal lens especially for video but their "normal" lenses aren't parfocal (well, not the ones I have, anyway).

 

If I knew anything about video I'm sure I would miss it. But I don't so I don't.

 

Gordon

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