Who said the VG20 does not have -ve gain?

[Craig Marshall]

I've read numerous reports lamenting the fact that the VG20 does not have an inbuilt ND filter and suggesting that instead, a 'negative' gain setting would be appropriate. For example: -6dB -3dB, 0dB, +6dB, +12dB etc. This is a common feature in broadcast cameras and can be very handy in some situations. Well, the VG20 does in fact have a negative gain feature, an inbuilt gamma lift/highlight compression circuit as well as a colour temperature adjustment feature. You just have to know how to set the camera up.

As I recently ditched the 'kit' SEL18-200 zoom in favor of a set of Carl Zeiss prime lenses, I changed the programmable thumb wheel over from 'Iris' to 'Exposure Compensation' or 'AE Shift'. When using fully manual lenses, this is a very handy feature as you can quickly and easily fine tune the exposure up to +/- 2 stops either side of where your manual iris is set. If your gain is set to 0dB, then this option can give you up to 2 stops of 'negative' gain. ie: a quarter of the sensitivity so similar to fitting a 2 stop ND filter.

The camera's auto back-light compensation option can be used to lift the centre of the waveform and compress the image without pushing the signal above 100 IRE. It is in fact a type of 'knee compression' circuit and very handy when shooting back lit scenes. For example, when you shoot a dark face against a bright sky.

The third feature often overlooked in the Vg20 is the fact that you can set the thumb wheel up to adjust the white balance compensation. Although I don't advise it, if you really must add some basic 'color correction' to your image during a shoot, this feature would allow adjustments of the image from 'warm' to cool' and coupled with say, a digi-con filter can achieve a 'flat' desaturated image.

[John Vincent]

Absolutely great tips Craig.

Knew about the color temp shift (very nice for golden hour shots), but didn't know about the 'AE Shift' ability to give negative stops.

[Chris Barcellos]

So with that tip, are you noting any artifacts or other issues with the resulting footage ?

Ran this simple test. Nice to get shallow depth without stacking ND's

Using Process suggested by Craig Marshall - YouTube

[Craig Marshall]

No, I cannot see any additional artifacts shown with this exposure adjustment.

Note: if +6dB of gain is equivalent to 1 extra stop of light and +12dB gain = 2 additional stops, then we can assume if we set gain at 0dB then use exposure compensation to dial in 'negative gain', this should (might?) equate to -6 and -12dB gain respectively.

[Ron Evans]

I don't think it works quite like that. The camera has absolute gain limits that the AE shift will not exceed. The AE shift just biases what the camera auto exposure has decided to use . I use all the time on my Sony's as the stock auto exposure certainly on the small Sony's is too hot. On the SR11 and XR500 I have them set at -1 for normal use and -3 in the theatre. On the CX700 and NX30U have them set at -0.2 EV for normal use and -0.7EV in the theatre. On my NX5U I have AE shift set at -2 and spotlight set to two of the programmable buttons and when I need to use auto exposure set iris at f3.4 ( means I can zoom without lens ramping ) and switch in AE shift. The camera will then manage exposure with iris at f3.4 fixed and vary gain subject to the AE shift at -2 and I also have a gain limit set at 12db. If the actors are in lots of spotlight I also then switch in the spotlight feature which I think manages knee and gamma automatically to manage detail in the highlights. If on the NX5U it gets really bright the gain will go to -6db, the camera limit and then ask me to switch in ND filters. The same will be true for the VG series I think so you will still have to use an ND if it gets really bright as once you reach the limit of the sensor you will need to reduce light input. I am sure all the Sony's work the same way all the AE shift does is make the image darker or lighter from where the stock auto exposure thinks it should be. As the name implies Auto Exposure shift.

Ron Evans

[Craig Marshall]

Yes, AE Shift will work that way if Auto Exposure is selected. AE Shift is normally used as a handy +/- 2 stop 'trim' feature for the camera's Auto Exposure setting but I'm using a fixed exposure (in my case, 0dB gain, shutter @ 1/50th, frame rate @ 50i) and my VG20 is fitted with manual 35mm FF prime lenses with manual iris rings. With my VG20's programmable thumb wheel set to 'AE Shift' and by dialing it into the -ve region, it would seem that I can mimic the effect of a placing 2 stop ND filter in the matte box. This implies AE Shift is controlling exposure ie: ISO (or gain in this case) so negative gain would be possible.

PS: I'll run some more tests this week when the C/Y>NEX 'Speedbooster' arrives from Hong Kong.

[Ron Evans]

All parameters have to be fixed not just gain. If only one parameter like gain is fixed then the camera will operate all the others, iris or shutter speed to control the camera and an "A" will appear next to those parameters on the LCD. If you set all to manual I do not think AE will work, certainly does not do so on my NX5U and would be strange to have a feature called Auto Exposure shift when everything is in manual so nothing left for the feature to control. Setting the auto/manual switch to manual only tells the camera you wish to control the parameters it doesn't fix them in manual, this is common practice across the Sony line and confusing for a lot of people. In manual an A appears next to all the parameters on the LCD and they stay in automatic operation until the parameter is selected for control. If you then set gain to 0 db an " E " is then set next to gain but if "A" is still next to iris and shutter speed they are still in automatic and AE shift has something to control. Look at the data code on the recorded file too as a check of what is happening. It's Sony's way of achieving the Tv/Av that Canon cameras have. Even with your manual lens there is still shutter speed left for the camera to control if you have not set that as well.

Ron Evans

[Chris Barcellos]

Originally Posted by Ron Evans

The same will be true for the VG series I think so you will still have to use an ND if it gets really bright as once you reach the limit of the sensor you will need to reduce light input. I am sure all the Sony's work the same way all the AE shift does is make the image darker or lighter from where the stock auto exposure thinks it should be. As the name implies Auto Exposure shift.

Ron Evans

Wish I had more time to check this out Ron and Craig. My little test was 1:30 in afternoon, absolute bright sun, no overcast. Hotest day this year so far. I wondered whether camera had auto changed shutter speed, but the panning does not indicate that high speed shutter look. Lens was a fixed non-auto 1980 's lens. Can't recall where to find it, but metadata should say something. Just can't recall how to get it out of the file.

[Noa Put]

The idea behind it seems interesting so I tried it on the ea50 with a manual only prime lens but it didn't work, only when the camera was in auto but then it also changed the iso and shutter. The ae shift is as far as I know only usable when the camera is running in automode to compensate over or underexposure when the camera get's it wrong in that mode.

I also think ae shift is no substitute for a nd filter like a variable one. If it would work it would still give you a very high shutter at bright days. No matter how you look at it, the vg20, doesn't have a build in nd like function that would enable you to shoot at 1/50th shutter at a bright sunny day. You will need a separate nd filter for that.

[Ron Evans]

Chris, you press data code on the remote when the file is playing back. Data code will appear bottom right showing date and time, press again camera settings and again will give GPS location. I am sure that you will find that shutter speed will change as you set AE shift if iris and gain are fixed. Fixing iris to control depth of field and setting a gain limit and with AE shift is a good way to operate. Something I do on my NX5U.
Ron Evans

[Craig Marshall]

I thought it prudent to edit this post to offer an explanation and additional information about the VG20's thumb-wheel operation when programmed to 'AE Shift'. Here are my camera a settings:

LENS: Carl Zeiss Contax 135mm F2.8 lens (F2.0 at the sensor with 'Speed Booster' attached)

Setup Menu:
Shooting without lens: 'Enabled'

Camera/mic Menu:
Frame rate: 50i
Shutter: 1/50th
Gain: 0dB
Thumb-wheel setting: AE Shift
Exposure: Auto

Watching the histogram in the viewfinder in a dark room, l have the lens' manual iris set wide open to F2.8. Enabling thumb wheel operation by pressing the 'Manual' button beside it, I adjust the wheel into the -ve region and the picture in the viewfinder gets slightly darker whilst the histogram rolls off to the left. As my Exposure is set to 'Auto', one can only assume the camera's electronics are changing the 'exposure' or shutter speed during programmed thumb wheel operation. Although, if you actually check the shutter speed, it 'appears' to stay set at 1/50th and Gain 'appears' to stay set at 0dB. When Exposure is set to Manual, thumb wheel AE Shift operation is inhibited.

(BTW, thumb wheel operation can be changed to any of the other five options by simply pressing and holding the 'Manual' button for a full second)

PS: My 'Speed Booster' is the purely 'passive' optical model with no electronics: C/Y to NEX 'Focal Reducer'

[Ron Evans]

Craig you need to check the data code in playback to see what is actually happening. The LCD indications on lots of Sony's do not always follow what the camera is actually doing. The data code usually does report the true camera settings. This is especially true of gain as in auto there is variable gain but in manual only switched positions so even on the data code it could be wrong !!! In some respects this is the value of using the Sony's ( or Canon's ) in semi auto mode with AE shift as it is possible to get exposures not easily possible in full manual with consumer cameras that switch iris in switched positions rather than a variable iris. Unfortunately even the AE shift is in fixed positions !!!

Ron Evans

[Steven Digges]

Originally Posted by Ron Evans

In some respects this is the value of using the Sony's ( or Canon's ) in semi auto mode with AE shift as it is possible to get exposures not easily possible in full manual with consumer cameras that switch iris in switched positions rather than a variable iris. Unfortunately even the AE shift is in fixed positions !!!

Ron Evans

Ron,

I was with you and agreed until now? The statement above does not make any sense to me? What are you trying to say?

Manual is manual. You can set the camera up to any setting physically available. Consumer cameras do not always do what you might expect them to do when any auto mode is enabled. They try to be smarter then a "amateur consumer" by controlling the camera as a "whole". For example, in full auto, when you have plenty of shutter speed left to go slower they will revert to iris or gain to adjust exposure and stay at 1/60 (example) to prevent blur and shake. If you want to avoid that you need to limit the auto functions until you get what YOU want.

Is'nt this thread about: can you or the camera control exposure beyond shutter, iris, and gain, with exposure compensation because the camera will use internal adjustments like knee and other parameters to achieve it? That does not make sense to me and I doubt it is possible but I thought that was one of Craig's original points??? Am I completely confused here?

Steve

[Ron Evans]

I was referring to the fact that the automatic adjustment do not need to be the fixed available parameters of full manual. In automatic the camera can control in a variable way not possible in consumer cameras. So by using AE shift the camera still has this control. I also think that in iAuto it will control parameters like knee just not available in manual operation on the consumer cameras. This is evident when using the spotlight setting. If you set them to full manual you loose this capability and have to set parameters to the values available. I have a few small Sony's, SR11, XR500, CX700 and NX30U and they work best in this semi auto mode. My comments are of course for these consumer cameras not a full pro camera with all the controls available.

Ron Evans

[Chris Barcellos]

Per Rob's discussion, I checked shutter speed and other information, and it showed shutter speed at 1/4000.