GH2 Exposure (Any Panny?) with Manual Lens RESOLVED?

Discussion in 'Panasonic Cameras' started by Boatman, Apr 20, 2011.

  1. I think I have figured out the problem and it will be of interest to all photographers that shoot indoors by natural light. The problem is COMPACT FLOURESCENT LIGHT BULBS!

    At lunch I tried to recreate my problem described in the earlier post and wanted to try natural lighting as well. Last night in the kitchen it was dark outside and I was shooting by the house lighting. Today, in the office, the lighting is tube type fluorescent lights. At home we are now using compact fluorescent lighting for almost all of our lights.

    As you may know, with AC current, all lights strobe at 60 cycles a second. Tungsten lights don't go 'out' between flashes so the strobing is not very strong. Fluorescent lights brighten and dim much more on each power cycle so they act as a 60-flash-per second strobe. Like movies, you eyes can't see this but your camera can. I'm going to go out on a limb here and state that the imager of our cameras is also strobing but I don't know at what frequencies. I do know that all computer pulse, that's how they are rated 2GHz, 3.2GHz, etc. I think stobing of the light source is raising havoc with the camera's sensor.

    I ran a bunch of tests in the same manner as last night. Since I was holding ISO steady, the speed was increasing as I opened the aperture of the lens. At about 1/100 of a second, thing start getting weird. Yellow streaking in the corners, green hues and this gets worse as the shutter speed increases.

    To prove this I ran two more tests. I shot a series out the window but with a little reflection from inside. In these shots the objects outside are fine but the interior reflection begins picking up funny yellow hues. I then held shutter speed steady and varied the ISO and f-stop for another indoor series of shots. From f-16 to f-1.4 and ISO 12800 to 200 (more or less, I didn't take exact notes) and all the images are approximately the same brightness but the coloration varied quite a bit. I then changed the white balance from auto to outdoor; this gave the most accurate coloration but more importantly held the reading steady. The results were even better though not as exact as you might expect. My suspicion is that the metering system is still being thrown off a bit by the stobe of the fluorescent lights.

    I ran one more test. I put the camera into ultra high speed multi-frame mode and shot at several shutter speeds from 1/40th to over 1/500th. You can see the results right in the viewfinder! At speeds above about 1/50 you will see rolling bands of yellow (like TVs of old) crossing the screen. This is the images being captured at partial lighting and synching between the high-speed shutter and the AC cycle.

    So the lesson is all this is: Indoors by available light you must pay attention to your light source, not just for coloration, but also shutter speed relative to lighting type. If you are in fluorescent lighting, which is more and more common now, you need to use a slow shutter speed. High shutter speeds are going to give inconsistent results due to the capturing of a partial wavelength of AC current.

    So, none of this explains why the best pictures I got last night were at f1.4and 1/3200, nor does it explain why I haven't seen any problems with the 14-140. I suspect that the 14-140 is so slow that my shutter speed is always sufficiently low with it and maybe I'm just really quick with the shutter and took the f1.4 adapter photos right at the peak of the AC cycle. :thumbup:
     
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  2. sprinke

    sprinke Mu-43 All-Pro

    Apr 5, 2011
    Pasadena, CA
    Debi
    Very interesting conclusions. They are actually consistent with my observations ... we have all CF lighting in our house and I had been seeing underexposed shots with the manual lens inside but not outside the house.

    I'm actually intrigued to try a side-by-side comparison between my 50mm 1.4 manual lens and my 14-140mm lens. Try to recreate the same settings and same location and see the differences. Perhaps the 14-140mm lens, being a fancy piece of electronic equipment, has something built-in to compensate for the strobing?
     
  3. I doubt it. I suspect it's just that the 14-140 is alway shooting at slow shutter speeds due to its low f-speed. However, a controlled experiment getting the shutter speed up to 1/250 or so would be really interesting.
     
  4. sprinke

    sprinke Mu-43 All-Pro

    Apr 5, 2011
    Pasadena, CA
    Debi
    Did a quickie controlled experiment over my lunch break today. Took pictures with both lenses at ISO12800, f/5.6, 1/320 (everything on complete manual).

    No visible difference between the two. Hm.
     
  5. I don't know what to say. I'm feeling a little foolish. I can't recreate the problems I had last night but I have the weird shots in Picasa to prove I'm not nuts.

    I just re-tried all this. With the 14-140 in both single and high speed burst mode, I cannot see any issues at shutter speeds from 1/50 to 1/500. This is with CFL light and with tube fluorescent blubs. With the 50mm Takumar I'm getting consistant good exposures on single shots at all shutter speeds and f stops. In high speed burst mode I do get banding in the viewfinder during the shooting at speeds above 160. Tube fluorescent bulbs are worse at the same speeds.

    The following two sets of photos are taken with the Tak 50mm in A mode. All have +1EV. All had the histogram in the camera pretty centered. In the first set the histogram shown in Picasa is way to the left. In the second set it is pretty even across the full scale. Note the clock in the first picture. The 8 is missing - dropped out by the sync of the LCD and the shutter at 1/1300. In the second set the clock totally blacked out at 1/800.

    There is something going on here, but I confess I can't fully explain it. :frown:

    f1.4 1/1300 ISO3200


    f8 1/50 ISO3200


    f1.4 1/800 ISO6400


    f8 1/30 ISO6400


    And just to make me a little crazier, as I was re-trying this with a different exposure area setting to see if this makes a difference (it does), the shutter adjustment locked on me again. Stayed at 1/30 from f16 to f8 - getting really bright here - and then I switched from A to S and back, the problem cleared. Something different going on there.
     
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