GH2 exposure shifts during zooming with 14-140mm kit lens

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davidp158

Well-known member
When I zoom in or out using the Panasonic 14-140mm kit lens, I see pronounced shifts in exposure. I have tried various manual settings, trying to lock the exposure, but can't seem to work it out. I thought that using the manual exposure setting in the creative movie mode would lock the exposure, but its not working as expected. I have also tried aperture priority mode, but it doesn't offer any improvement. BTW, when zooming the lens, I hear a faint "click" each time there is an exposure shift. I presume this is a mechanical change in the aperture. I don't have another zoom lens to determine if this exposure shift is due to the 14-140mm lens, or something going on with the GH2.

Is this exposure shift a problem with the 14-140mm kit lens not being a "constant aperture" lens? I was hoping that I could lock the aperture in manual mode. I understand that as the lens changes focal lengths, there will be a change in the light hitting the sensor, but I hope to be able to tweak under and over exposed video in post. The exposure shifts I am getting now are just too fast and pronounced to tweak.

Here's a link to a video that shows these exposure shifts (approximately at 2, 4, 6, 7, 9 and 10 seconds):

http://vimeo.com/41302092

Any suggestions on how to eliminate or minimize this would be appreciated.

cheers,
Dave
 
This is due to the 14-140 being a variable aperture lens, which means sadly there's not a solution to the exposure changing as you zoom.
 
DevonH and Gymnut808 - Thanks for the prompt replies! I sort of thought the issue may be that the 14-140 lens isn't a fixed aperture, but was hoping there was a manual mode that would over-ride any exposure shifts. At least for once the problem I experienced isn't one induced by ME! LOL... Eventually I will save up for better glass, but I have plenty to learn before I maximize what I have.

I presume that the aperture is electronically, not mechanically, linked to the exposure system. Meaning, the GH2 imposes an aperture change depending on the metering system, and not the lens' focal length. I'm wondering if there is a way that locking the aperture could be hacked somehow. Wishful thinking?

cheers,
Dave
 
Yes, wishful thinking. The same thing exists in other brands of gear, Canon users have the same problem with no real solution.

The good news is that zooming while recording has been so overdone in the past it is looked at as an extremely "amatuerish" filming technique. So you are advised not to do that. If such is needed a "dolly" movement in or out is much preferred.

So even if you could zoom while filming, you really don't want to.
 
Odd.. there was another person who had the same complaint...

Here's my response to that thead:

-----
A couple of points...

1) The 14-140 limited to f/4 and smaller. Hence, it will not 'compete' with a 1.4/2.8 type lens most people would think about for 'low light', the way to 'correct' for that is to use a higher ISO number than what one may use with a faster lens, since for moving pictures, the frame rate sets the absolutely longest shutter speed, of 1/24, 1/30, second depending, and the 'recommended' shutter speeds are 1/2 the frame rate, which are 1/48(1/50) and 1/60 sec. respectively.

2) Many zooms for still cameras will change 'aperture' during zooming. The 14-140, starts off at f/4, and ends up somewhere around 5.6 or so. So, just by that fact alone, you will get level changes... a 'constant' aperture lens, that is $$$ lens... will correct that.

3) There are also focus shifts during zoom... and so even more $$$ are required to correct that.

The 'corrections' are to get a constant aperture zoom, along with parfocal, to correct for these two defects...

What do you want for a lens that is around $700 new...

For example, a Nikon 24-70mm f/2.8G ED, listed on the Nikon USA page, has a recommended price of $1889.95... Don't know what the street price is, but it's most likely still 3x the Lumix lens... How one tells 'constant aperture' on Nikon lenses, and I presume other manufacturers do this as well.. as the Lumix 14-140 is listed as f/4-5.8... is if the f-stop has a range, like 4-5.8, then it is variable aperture, if it is a single number, it is constant.

For 'cine' lenses, the price range starts getting up in to the $30K range...
 
This is the main reason why I got a B4 broadcast lens for my GH1. I have a 34-300mm-ish lens (after conversion) with a fixed f/3.4 aperture for a little over $200. Of course, you need a $250 adapter to use it and it weighs like 5 pounds but it gives you great control over your image for a fraction of the cost for a still lens. The broadcast lens I have is probably 15 years old but it works just fine. I don't know if you get as crisp of an image as a more expensive lens since they were made for sd cameras with 2/3" sensors but there are plenty of YouTube videos showing off the quality. I used to shoot local tv news for over a decade so I am intimately familiar with these types of lenses which played a big factor in my decision to go this route. Still, it was quite the rabbit hole to go down.
 
I'm interested in trying this out. How do you power the lens?
Which adapter are you using?

thanks
 
I bought an adapter with a tripod mount built-in, but my tripod has a big plate which got in the way of the 2x extender on the lens. I had to find a way to raise the adapter mount about a half inch to make it work. Just search ebay for b4 to micro 4/3 adapters. I paid $250 for the adapter which was more than I paid for the lens, but I wasn't able to find anything cheaper at the time. Maybe you will have more luck. My lens is a Fujinon which is powered by a 12 pin hirose connector. I just bought a 12-pin to d-tap conversion cable for the lens this morning. Up to now I have just been operating the lens in manual mode with no power because I had spent enough on the lens and adapter already. The cable I just bought cost $65 and power to plug it in will probably cost over $100 so it all adds up really fast.
 
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