14-140 exposure shift during zoom?

tacotim

tacotim

Well-known member
I am getting exposure shifts when zooming with my lumix 14-140. Can anyone else confirm that this happens to them? Shutter is locked at 180degrees, aperture is on manual at 7.1 iso is set to 400. Zoom in and out and there is very obvious exposure shifts. It only happens for me with the lumix lens. And it does the same thing when i mount it to a GH2 body. I will post the video when i have a chance.

thanks, tim
 
It's not an anomaly, it's exactly what it'ssupposed to do.

It's not a constant aperture zoom. It gets slower at the telephoto end.

And even though it might be set at a certain aperture, you can bet that the same aperture is not the same total light transmitted at various focal lengths.
 
tacotim said:
I am getting exposure shifts when zooming with my lumix 14-140. Can anyone else confirm that this happens to them? Shutter is locked at 180degrees, aperture is on manual at 7.1 iso is set to 400. Zoom in and out and there is very obvious exposure shifts. It only happens for me with the lumix lens. And it does the same thing when i mount it to a GH2 body. I will post the video when i have a chance.

thanks, tim
Click to expand...

Jan said there will be a firmware update for the lens that will correct this. I posted this concern on another thread.
 
Kholi, i don't think what i'm experiencing is what you are referring to,
it's really a pretty exaggerated fluctuation. Video is uploading, will post the link shortly.

Brian, i'd love to see a link to the thread you are talking about. Tried searching for it, but couldn't find it.

thanks, tim
 
tacotim said:
Kholi, i don't think what i'm experiencing is what you are referring to,
it's really a pretty exaggerated fluctuation. Video is uploading, will post the link shortly.

Brian, i'd love to see a link to the thread you are talking about. Tried searching for it, but couldn't find it.

thanks, tim
Click to expand...

Mm, no, I know exactly what you're talkin about. I had a 14-140 and GH-1 for a while and I know exactly how it behaves. F-Stop does not indicate T-stop, or total light transmitted at any given Focal Length.

Even if you were to close the lens all the way down and zoom, you would still get the same obvious shift.

When you zoom in or out it may go brighter or darker for a brief moment as well, that's the camera and lens not playing well together.

It would be interesting to see a Lens Firmware update that could fix that, where's that page?
 

If this is what i should have expected, then please forgive my ignorance. I understand the concept that the lens has a larger aperture at the wide end, but do i have unrealistic expectations to have the light level remain somewhat consistent once i close down beyond the largest aperture the telephoto end supports?

The lens on the HVX200 for instance is I believe a 1.4 on the wide end and a 2.8 on the tele. If i close to a 2.8 i can zoom in and out to my hearts content without any exposure shift at all.

The thing about what i'm experiencing now is that it acts like it's on some kind of auto exposure. When i pull out, the image brightens to overexposure and then comes back down to proper exposure.

thanks, tim
 
The lens is F4 at the wide end and F5.8 at the long end. One stop is a big difference!

Therefore the wide end allows (slightly more than) twice as much light to "pass" thru to the sensor than the wide end passes thru.

Conversely. 1/2 as much light is passed thru from the long end compared to the wide end..

Difference is the same as a 100 watt light bulb vs a 50 watt light bulb or a 1000 watt vs a 500 watt etc......
 
tacotim said:

If this is what i should have expected, then please forgive my ignorance. I understand the concept that the lens has a larger aperture at the wide end, but do i have unrealistic expectations to have the light level remain somewhat consistent once i close down beyond the largest aperture the telephoto end supports?

The lens on the HVX200 for instance is I believe a 1.4 on the wide end and a 2.8 on the tele. If i close to a 2.8 i can zoom in and out to my hearts content without any exposure shift at all.

The thing about what i'm experiencing now is that it acts like it's on some kind of auto exposure. When i pull out, the image brightens to overexposure and then comes back down to proper exposure.

thanks, tim
Click to expand...

Yeah, see my post above yours. I knew what you were talking about. haha. And, yes, it's very annoying.

There is a way to defeat it, I just can't remember what I had to do. Someone else might be able to chime in, but it also has to do with the way the body is communicating with the lens.

If you listen to it, when you zoom out, you can hear the aperture readjusting as you roll the barrell.

Edit: Okay I remember why it's doing that...

It's because the lens and camera are attempting to keep the aperture the same, and going back to the original explaination, an aperture of F5.8 @ 14mm does not allow the same amount of light in as F5.8 @ the 140mm end. So what it's doing is keeping the aperture at F5.8 even when you zoom out, but it's not the same amount of light.

I think that was the conclusion we came too, it's been a while.
 
Kholi said:
Yeah, see my post above yours. I knew what you were talking about. haha. And, yes, it's very annoying.

There is a way to defeat it, I just can't remember what I had to do. Someone else might be able to chime in, but it also has to do with the way the body is communicating with the lens.

If you listen to it, when you zoom out, you can hear the aperture readjusting as you roll the barrell.
Click to expand...

Wow, well if there is a way to defeat it i'm all ears, otherwise this lens becomes much less useful to me.
 
Make sure all of the auto exposure methods are turned off. Does that camera have an iExposure thing? If so, turn it off.

I'd say turn off "lens recognition" or whatever it's labeled as in the AF100, see if that helps. But, you wouldn't be able to adjust the iris or anything unless it's on.

When you DO turn lens recognition off, does the lens' iris lock at whatever you had it set to prior? You could set it, turn off Lens Recognition, then shoot?

I didn't use the 14-140 much when I had it... I just can't remember what we did to alleviate that minor hiccup.
 
Kholi said:
Make sure all of the auto exposure methods are turned off. Does that camera have an iExposure thing? If so, turn it off.

I'd say turn off "lens recognition" or whatever it's labeled as in the AF100, see if that helps. But, you wouldn't be able to adjust the iris or anything unless it's on.

When you DO turn lens recognition off, does the lens' iris lock at whatever you had it set to prior? You could set it, turn off Lens Recognition, then shoot?

I didn't use the 14-140 much when I had it... I just can't remember what we did to alleviate that minor hiccup.
Click to expand...

hmm, yeah, lens check is off, but it still seems to recognize the lumix. No iExposure on this camera, DRS is off. Still no improvement. Let's hope for a firmware adjustment on this one.
 
tacotim said:
Wow, well if there is a way to defeat it i'm all ears, otherwise this lens becomes much less useful to me.
Click to expand...

I am using the same lens on my unhacked gh1.However after loading the latest firmware Ver.1.4 upgrade onto the camera i am now suffering the same thing as you.One workaround is to set the AF/AE lock at the point of filming.This works for me in manual focus.
 
So, I have the latest camera and lens firmware (1.15 for the AF100 and 1.4 for the 14-140mm), and I'm still experiencing this same problem. Not only does the exposure fluctuate during any snap zooms, but the lens seems to lose focus briefly as well, before snapping back to sharp and the original exposure. Just to re-iterate, this is not just a result of the lens being faster on the wide end; it's very rapid, distracting fluctuations during the zoom. It doesn't seem to happen during slow zooms, but during more rapid, documentary-style reframing type zooms.

I've never seen any other zoom lens, parfocal or not, behave like this. Hopefully there's some kind of solution?
 
Face Recognition? What's that?

I'm in full manual everything. I don't think I've ever used autofocus. (Well, maybe I turned it on once just to see if it worked...)

From what I've been reading in other threads, though, it sounds like all the Panasonic m4/3 zooms might do this, and maybe even some of the Olympus? If so, that is a serious bummer. Can anyone confirm or disconfirm this?
 
Sounds like what you found happening with the Olympus zooms is a little bit different than what happens with the Panasonic 14-140. Does the fluctuation with the Olympus lenses depend on the speed of the zoom? The Panny seems to zoom okay if you do a real slow, 1970's style (or 80's/90's corporate video style) zoom, but if you try a kung-fu snap zoom or a documentary style short-quick zoom, you can see the lens isn't able to keep up and seems to lose track of both the focus and the exposure simultaneously, if only for a moment. It's a very odd thing for a lens that is supposedly optimized for video to do.

I have a Tamron 17-50mm that I use all the time on my 7D, and even though it's a fairly cheap, auto-focus optimized lens meant for still photography, I can zoom it back and forth as fast as possible in video mode and the exposure stays completely locked. The focus plane may shift ever so slightly, but it doesn't go completely soft for a moment the way the Panasonic 14-140 does.

In a different thread awhile back, I think Jan suggested there might be a firmware update that would help this, but so far, that doesn't seem to be the case. Jan?

Also, Barry Green; You've been a fan of the 14-140 for awhile; does yours do this same thing, and does it bother you?
 
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