GH2 12-35mm X - Constant Aperture through Video Zoom?

B

bmillz

Member
Apologies if this is a stupid question.
One of the reasons I was excited about the 12-35mm lens was the idea it would have a constant aperture, so that I could do a slow zoom on a character and I wouldn't see the light change or flicker. But, it's definitely happening with this lens.
Check out this video:
https://vimeo.com/48662408
password: 1235
I've messed around with the exposure settings in movie mode. But, all of them do the same thing. Am I doing something wrong? Or was I wrong to expect this lens to do that?
PS. It should be noted: I used the new "Apocalypse Now" hack with the lens:
personal-view.com/talks/discussion/4391/apocalypse-now-quest-for-simulated-444-smooth-cinema-quality-driftwood-cbrandin-bkmcwd?Sort=newest
 
bmillz said:
Apologies if this is a stupid question.
One of the reasons I was excited about the 12-35mm lens was the idea it would have a constant aperture, so that I could do a slow zoom on a character and I wouldn't see the light change or flicker. But, it's definitely happening with this lens.
Check out this video:
https://vimeo.com/48662408
password: 1235
I've messed around with the exposure settings in movie mode. But, all of them do the same thing. Am I doing something wrong? Or was I wrong to expect this lens to do that?
PS. It should be noted: I used the new "Apocalypse Now" hack with the lens:
personal-view.com/talks/discussion/4391/apocalypse-now-quest-for-simulated-444-smooth-cinema-quality-driftwood-cbrandin-bkmcwd?Sort=newest
Click to expand...


Lens does not flicker, you have some settings set to Auto in your camera. Make sure EVERYTHING is set to manual. Even check your LCD settings
 
Everything is set to manual. Tried it unhacked and hacked. If I shoot indoors and walk outdoors, the exposure doesn't reset - everything is blown out. Not sure what I'm doing wrong here.
 
bmillz said:
Everything is set to manual. Tried it unhacked and hacked. If I shoot indoors and walk outdoors, the exposure doesn't reset - everything is blown out. Not sure what I'm doing wrong here.
Click to expand...

If you're shooting full manual the exposure shouldn't "reset" because an F2.8 indoors may be at exposure but it won't be outdoors(sans ND filters), so yes "everything" will be blown out. If you want the camera to handle your aperture changes, I believe you need to set the camera for shutter priority where you designate your shutter speed(1/50, 1/60, etc.) and the camera will figure out the aperture settings based on what it calculates to be proper exposure.
 
Gymnut808 - What I meant was, indoors: when I zoom in on an object, I can see the aperture changing. Little light flickers in the image. It's in the vimeo I posted. JFR suggested that I wasn't in full manual mode. And I said that when I walked outdoors it didn't reset the aperture, which leads me to believe I am in full manual mode. I don't want the image to change aperture is the problem I'm facing.
 
Ah okay I see what you mean; The exposure change is very subtle. Are you able to tell at what focal length the exposure change occurs and does it only happen when shooting wide open? Or across all aperture sizes?
 
It happens across all aperture sizes. If I had to eyeball it from 12-35, it happens around 18 - 27 - 35
 
Watched your footage and that is ... odd. I'll be watching this thread with interest to see what the outcome is.
 
Yeah, this is bumming me out.

I shot some outside stuff here and yet again it creeps up:
https://vimeo.com/48673906
password: 1235

My apologies for the yapping dog in advance.

Considering the existence of the Panasonic AF100 and the rumors surrounding the GH3 being more "pro video shooting friendly" - I thought for sure this would be "the lens". Couple that with Panasonic's advertising and well...This just sucks.

I hope there's something in camera I'm missing, but if not, I'll have to send it back.

EDIT: I just found this video. At 50 seconds in, there's a zoom with the same problem: https://vimeo.com/46550122
 
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I rented and used this lens for a shoot and know for a Fact it does not flicker, something is either wrong with your lens, camera or just a basic setting you have wrong.
 
Well, it's not the settings, cause I've tried every one.

If it's the lens - then it might be the lens. But, considering other videos online have the same problem...I'm not sure.

I'll keep it around for another week to see if there's any solution. If you've used this lens before and have video of you zooming in or out on something through the entire 12-35 range, I'd love to see it. I'd love for this to be a faulty lens, trust me.
 
bmillz have you tried using the AE lock function? I do remember having the same issue with my Nikon AF-S 24-70 f/2.8 nano (on a Nikon body BTW). I fixed it in the post by using a plugin in Premiere called GBdeflicker.

I also recall when we were shooting with the Canon 10-22 lens which its aperture is 3.5-4.5 so in widest zoom will be f/3.5 and the longest zoom is f/4.5 so there are changes in aperture during zoom. I use a tape to cut the connecting between the lens and the body so it turned out to be a very smooth aperture change.
 
It looks to me like what you're seeing is the iris changing to allow for the same amount of light coming in. That's what's really meant by 'constant f-stop". It doesn't necessarily mean the iris doesn't change, it means the amount of light coming in doesn't change, and as you zoom, the iris needs to change in order to keep that same amount of light.

The problem is that none of these 'stills' lenses are made with a proper iris, they all step through instead of being continuously variable as a proper iris should be.
 
Jim Simon said:
It looks to me like what you're seeing is the iris changing to allow for the same amount of light coming in. That's what's really meant by 'constant f-stop". It doesn't necessarily mean the iris doesn't change, it means the amount of light coming in doesn't change, and as you zoom, the iris needs to change in order to keep that same amount of light.

The problem is that none of these 'stills' lenses are made with a proper iris, they all step through instead of being continuously variable as a proper iris should be.
Click to expand...

Jim, that explains a lot. I've seen little exposure "stutters" with my 14-140 when it's set to f5.8 or higher (so that the f-stop should be constant from one end of the range to the other). Thank you for this post--it cleared up a mystery for me!
 
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So I've been trying out the zoom feature and yes, there are visible and audible adjustments as one travels through the zoom range. On my lens two adjustments appear, one around 23 and the other at 15 mm or so. Not good. I hope Panasonic addresses the issue if they can. In the meantime, zooming if required will have to stay within those ranges.
 
Sadly, and I mean sadly, the lens was returned today. I'm hoping that Panasonic does something about this issue, and if they do, I will repurchase the lens. However, based on their response to the issue people had with the 14-42 X pancake, I'm not holding my breath. If you don't need to zoom in video mode, the lens is indeed beautiful, but I think for the price, they should have got this one right.
 
I've seen strange flickering or exposure jumping around when manual zooming with panasonic 14X140 lens. Not just a straight iris up or down to compensate for variable f stop. Focus also shifts pretty dramatically.

When using 3rd party lenses with lens adapters, I don't see either the focus shift or exposure jumping problem, even with a variable f stop lens.

Both times, camera settings were in full manual.

There is some strange exposure/focus issues between the panasonic lenses and the GH2 camera.
 
I have this with the 14-140 lens. I'm always moving the camera so it is a constant problem.
Is there a lens that does not change the exposure in steps when in shutter priority mode
 
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