20mm f1.7 - soft focus????

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pix2pixels

Well-known member
Panasonic Australia marketing of the 20mm f1.7:

Features & Benefits

This bright F1.7/ 20mm (35mm camera equivalent: 40mm) fixed focus lens produces bright photos with a dramatic soft focus even in dimly lit locations....
 
I see people using the term "fixed focus". I always thought fixed focus means, you cannot focus that lens. I know you can focus the 20mm f1:7. So, why that term? Do you mean single focus lens,or prime lens? Just wondering.
 
RogerB1 said:
I see people using the term "fixed focus". I always thought fixed focus means, you cannot focus that lens. I know you can focus the 20mm f1:7. So, why that term? Do you mean single focus lens,or prime lens? Just wondering.
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The quote you are Referring to comes from panasonic marketing. I believe they are advertising that the lens has a fixed focal length of 20mm (40mm equivalent on the GH1). A prime lens is a lens with a fixed focal length, but that is independent of its "focusing" abilities. All this is saying is the lens is not a zoom lens with a range of focal lengths supported. The lens has a focusing motor, but focusing doesn't change the focal length of the lens.

Panasonic is also trumping the len's low light capability and the relatively shallow depth of field it provides wide open. Nothing really new in that statement, and it has nothing to do with the ability of the lens to focus.

For more info both dpreview (http://www.dpreview.com/lensreviews/panasonic_20_1p7_o20/) and slrgear (http://www.slrgear.com/reviews/showproduct.php/product/1295/cat/68) have very positive reviews of the lens. Sample pictures can be found as well so you can make up your own mind.
 
Regardless of what Panasonic marketing is saying isn't the fixed focus term correctly applied to a zoom lens that doesn't change focus while zooming? Is there another name for that?
 
Ben_B said:
Regardless of what Panasonic marketing is saying isn't the fixed focus term correctly applied to a zoom lens that doesn't change focus while zooming? Is there another name for that?
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No, fixed focus usually means that you cannot change the focus, it's usually used for lenses that are permanently set at their hyperfocal distance.

A lens that doesn't change focus while changing focal lengths is called a "zoom" lens. (or, much less commonly, a "parfocal").

A lens that does change its focus while changing focal lengths is called a "varifocal".

Unfortunately the term "zoom" has been commandeered to be used to apply to any lens capable of multiple focal lengths, but historically zoom has been used for lenses that maintain focus throughout the focal range.
 
That's the terminology I was looking for, thanks Barry.

I guess an example of a camera with an actual fixed focus would be a holga or a disposable film camera, etc.

Do you know offhand if the GH1 kit is varifocal or a zoom? I was trying to do some tests with it....I had assume it was a proper zoom but now I'm less than sure, but I didn't have my tripod with me at the time.
 
Barry_Green said:
I'm pretty sure it's a parfocal zoom, but Jack has my camera right now so I can't verify at this moment.
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If I understand correctly this means that with a parfocal lens once you lock focus on a subject you can "zoom" in and out and the subject will remain in focus. Is this correct, or do I have it backward? If this is the case then either the lens is not parfocal or I am doing something wrong as I usually have to readjust focus once I change the focal length ("zoom"). I think that the autofocus (if used) is fast enough with slow changes in focal length such that it may make the lens behave like a parfocal since the auto-focusing action is pretty quick.

Thanks for the clarifications!
 
From my limited knowledge of English and photographic terms, soft focus means soft focus. A lens can be described in layman's terms as sharp or soft. There are lenses designed for portrait only with a specific softness (sometimes variable), just look at Portragon, Petzval, Cooke.
 
If I were you I'd stop listening to Panasonic marketing on anything short of technical details and simply look at pictures.
 
Barry_Green said:
I'm pretty sure it's a parfocal zoom, but Jack has my camera right now so I can't verify at this moment.
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On my GH1, the 14-140mm kit lens is almost (but not quite) parfocal. i.e. with the camera mounted on a tripod, if I manually focus (w/ focus assist) at 140mm and then zoom all the way out to 14mm, the focus will be slightly off. But the adjustment is minor, so it could be an issue with my camera or lens or both.

HTH - Mark
 
BitMaestro said:
On my GH1, the 14-140mm kit lens is almost (but not quite) parfocal. i.e. with the camera mounted on a tripod, if I manually focus (w/ focus assist) at 140mm and then zoom all the way out to 14mm, the focus will be slightly off. But the adjustment is minor, so it could be an issue with my camera or lens or both.<br />
<br />
HTH - Mark
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I've played with the zoom some more and I think the 14-140 lens tries to mimic the behavior of a parfocal useing the lens' autofocus mechanism. I used the focus assist and manual focus to focus at 140mm focal length. I then did a quick "zoom" back to 14mm. When looking through the EVF I see the image go out of focus and snap back into focus (or near focus). The same thing happens when re-extending back to 140mm. The autofocus adjustments aren't perfect though and a series of quick zoom adjustments results in a completely out of focus subject. If the zoom changes are slow the effect is less pronounced. I can also hear subtle clicks from the lens as I zoom which I presume are the autofocus motor. I was in full manual focus mode and had OIS off.

I don't think this really affects shooting much as not much zooming is done while recording and I don't trust the focus to stay close while zooming anyway. It is interesting to me that it appears that the focus motor appears to be active even in manual focus mode. I'm speculating that Panasonic is trying to make the lens act like a fancy parfocal when it isn't actually a parfocal.

Does anyone else find this at least a bit curious, or at the very least confirm, or refute this observation?
 
If that's true the main issue I can think of would be the pointlessness of zooming in to get focus and then zooming back out again, you know, that move many of us use with our video cameras. Hmm.
 
holdingpattern said:
I can also hear subtle clicks from the lens as I zoom which I presume are the autofocus motor.

{snipage}

Does anyone else find this at least a bit curious, or at the very least confirm, or refute this observation?
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While I do hear some subtle clicks from the lens as I zoom out from 140 to 14mm, I do not hear them when I zoom in from 14 to 140mm. Nor do I hear them when the camera is just autofocusing (with no change in the kit lens' focal length) regardless of whether the camera is refocusing from, say, 1m to infinity or from infinity to 1m.

Maybe that's the aperture? - Mark
 
BitMaestro said:
While I do hear some subtle clicks from the lens as I zoom out from 140 to 14mm, I do not hear them when I zoom in from 14 to 140mm. Nor do I hear them when the camera is just autofocusing (with no change in the kit lens' focal length) regardless of whether the camera is refocusing from, say, 1m to infinity or from infinity to 1m.

Maybe that's the aperture? - Mark
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I believe you are right. The clicking went away when I set the shutter speed effect on. The clicking was probably the aperture adjusting to the different lighting at different zooms to properly gain up the live view display.

That said I get the clicking when zooming to or from 140mm. The clicks have to do with the light level not the zoom level, at least directly.

In any event the lens does not hold focus well enough to be usable after a quick zoom, but this is a non-issue for me, My lens is not a parfocal lens, nor do I expect it to be for the price, considering everything else it does so well. (low light being the exception)
 
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