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Old 7th of May 2010 (Fri)   #1
phil_5
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Default Difference between parfocal and varifocal

How do I tell which of my lenses are parfocal and which are varifocal? New terminologies to me.
Thank You
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Old 7th of May 2010 (Fri)   #2
egordon99
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Default Re: Difference between parfocal and varifocal

What lenses you own?

Last edited by egordon99 : 7th of May 2010 (Fri) at 13:20.
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Old 7th of May 2010 (Fri)   #3
kitacanon
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Default Re: Difference between parfocal and varifocal

If your shot is out of focus AFTER you zoom then that is a varifocal lens...
...if the image stays in focus after you zoom then it's a parfocal lens....

Most AF zooms are the former so be careful to focus AFTER you zoom to ensure that the shot (stays) is in focus....
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Last edited by kitacanon : 7th of May 2010 (Fri) at 17:09.
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Old 7th of May 2010 (Fri)   #4
egordon99
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Default Re: Difference between parfocal and varifocal

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Originally Posted by phil_5 View Post
Thank You Kitacanon. That's more along the lines of the intelligent answer I was looking for.
You asked us if the lenses you owned were parfocal vs. varifocal. I didn't know which lenses you owned. How is that not intelligent?
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Old 7th of May 2010 (Fri)   #5
wimg
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Default Re: Difference between parfocal and varifocal

A parfocal lens is a zoom lens that stays in focus at the same point where you set it regardless of the focal length you zoom to. Ideally you focus at the longest FL (for best accuracy) and then zoom to the desired FL. AFAIK, all current Canon zoom lenses are not parfocal. To a large degree this has to do with the fact that AF zoomlenses have relatively few and realtively loose focusing cams in order to make autofocusing possible with relativly weak focusing motors. Also, parfocal lenses are more difficult and more expensive to implement.

A varifocal lens is a zoom lens. Just a different name, used in the days when zoom lenses were new, and normally signifying a zoom lens with a very short zoom range, more useful for framing than actually zooming. The Tokina 11-16 could be considered a varifocal lens. Till this day I still use shorter zoom lenses as varifocal lenses, IOW, a prime with a framing option.

Kind regards, Wim

Last edited by wimg : 7th of May 2010 (Fri) at 16:46.
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Old 8th of May 2010 (Sat)   #6
kitacanon
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Default Re: Difference between parfocal and varifocal

Good call Wim...
We might add as well that "vari" can also refer to variable aperture, in which the widest aperture varies from widest FL to the longest FL...e.g. 28-105mm 3.5-4.5 which would be F3.5 @ 28mm and 4.5 @ 105mm and varies in between, e.g. F4 @ 70mm
....not a serious problem until you go from 3.5 to 5.6 where the smallest wide aperture may be too small to use shutter speeds fast enough to stop action indoors...that lens may have image stabilization (IS) to stop YOUR action (shakes/jitters) but IS doesn't stop action in FRONT of you.

There, now I think we've covered it...
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Old 8th of May 2010 (Sat)   #7
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Default Re: Difference between parfocal and varifocal

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Originally Posted by egordon99 View Post
You asked us if the lenses you owned were parfocal vs. varifocal. I didn't know which lenses you owned. How is that not intelligent?
Actually, he asked how to tell them apart. To explain that, you don't need to know which lenses he owns.
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Old 8th of May 2010 (Sat)   #8
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Default Re: Difference between parfocal and varifocal

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Originally Posted by kitacanon View Post
Good call Wim...
We might add as well that "vari" can also refer to variable aperture, in which the widest aperture varies from widest FL to the longest FL...e.g. 28-105mm 3.5-4.5 which would be F3.5 @ 28mm and 4.5 @ 105mm and varies in between, e.g. F4 @ 70mm
....not a serious problem until you go from 3.5 to 5.6 where the smallest wide aperture may be too small to use shutter speeds fast enough to stop action indoors...that lens may have image stabilization (IS) to stop YOUR action (shakes/jitters) but IS doesn't stop action in FRONT of you.

There, now I think we've covered it...
Thank you.

However, I hope you don't mind, but I don't agree with varifocal referring to variable aperture width or size when zooming. In the term varifocal two words are put together which say something about variation of something and about focal length. And that is all it really means, AFAIAC , variation of FL, or varying FL, unless the definition has changed dramatically since the early seventies and after the early nineties of last century .

Kindest regards, Wim
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Old 9th of May 2010 (Sun)   #9
kitacanon
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Default Re: Difference between parfocal and varifocal

No problem Wim...I was just thinking that while we were explaining the technologies of zoom lenses I might as well finish it off by explaining variable-apertures...just in case OP might not know that either...
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Old 9th of May 2010 (Sun)   #10
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Default Re: Difference between parfocal and varifocal

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Originally Posted by kitacanon View Post
No problem Wim...I was just thinking that while we were explaining the technologies of zoom lenses I might as well finish it off by explaining variable-apertures...just in case OP might not know that either...
Ok, thanks. It looks like I misunderstood your message in that case. Apologies for that.

Kind regards, Wim
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