Shutter speed "Auto"?  overexposure

J

jferris

Member
Hi

I just purchased a Dvx100a and have a question for members of the board. In the default "Auto" mode if I take the camera out into daylight it is very overexposed. Switching the ND filter to any setting but "off" corrects this or switchiing the shutter speed to "on" and manually increasing it. Is this normal? I thought that the "Auto" setting would take care of the correct exposure indoor or outside using shutter or iris priority without having to manually switch the ND filter or shutter speed.

It appears that there is no auto shutter priority when set to "Auto" with the shutter off. What is the shutter set at when it is in "off"?


Thanks Phil
 
Re: Shutter speed "Auto"?  overexposure

Hi Phil

The ND FILTER is completely separate to the IRIS. IRIS off is 1/48th (DVX100A I think? :-/ I have the Prequel version :D)

The Shutter speed is another separate element. To deal with exposure, concentrate on Manual IRIS and ND (Forget about Auto Iris except maybe to check the reccomendations)
 
Re: Shutter speed "Auto"?  overexposure

Thanks.

I see now after deciphering the manual that when the shutter is off (and camera set at 60i) that the shutter speed is set at 1/60. Even with an aperture of f16 it is overexposed. I am used to working with 35mm still camera so I understand these settings but I'm fairly new to manual video. In 35mm terms this would mean the dvx has a low light equivalent of setting a 35mm to 800asa?
So, it seems that when shooting outdoors in sunlight, a ND filter must be used or increasing the shutter speed. Which would mean that the dvx doesn't truly have an "Auto" setting.


Phil
 
Re: Shutter speed "Auto"?  overexposure

DVX is 640 ASA in progressive mode, and 1280 ASA in interlaced.

And yes, outdoors you will need to set the ND filter on. It cannot be automatically engaged, it must be manually engaged. (unless, perhaps, when you press the "full auto" switch, but even then I think it still needs to be manually switched in.)
 
Re: Shutter speed "Auto"?  overexposure

[quote author=Barry_Green link=board=Events;num=1082776178;start=0#4 date=04/24/04 at 07:27:12]DVX is 640 ASA in progressive mode, and 1280 ASA in interlaced.[/quote]

Really? I've measured my DVX to be 320ASA in progressive mode with normal exposure, as measured by shooting a grey card and setting the camera on Auto exposure. I then used my meter matched to shutter speed/angle and adjusted the ASA setting until I got the same stop the camera was using.

Is 640 a new measurment for the DVX-100A? I'm on a DVX-100. Another stop would be awesome.
 
Re: Shutter speed "Auto"?  overexposure

No, that's for the DVX-100, not the 100A. I measured reflected light on gray as well as in real-life circumstances, shooting outside, the sky, plants, indoors, low light, bright light, normal shutter, fast shutter, everything imaginable. It always came back as 640. We used two different meters, to make sure that a miscalibrated meter wouldn't be at fault. It's 640.

One thing you might check is the AE exposure bias -- in the scene dial defaults it's usually set to -3 on progressive, which will artificially cost you half a stop. Be sure to set that on zero to get the actual reading.
 
Re: Shutter speed "Auto"?  overexposure

Yeah,

I zeroed everything out before I did the meter reading, also did it with 2 meters and under both natural and artificial light. As suspected, it was the 100/100A difference.

thanks for the clarification Barry and John.
 
Re: Shutter speed "Auto"?  overexposure

Hrmm,

I have to disagree with Barry here. I think the DVX100A has ASA closer to 320. That is, if he is saying that the DVX100A has 640 ASA. Of course, different MPED, Gamma setting would make the difference.

However, I've tried in several different situations, and have found that my tests were closer to 320. I used a Sekonic Gray card along with a Sekonic L-508 zoom meter and dome. I set the A. Iris and Mped to zero, white balanced properly, then set Gamma and Matrix to Norm and did my test.

I know for a fact that Cine in DVX100 has a different curve than 100A, so that may be the difference if there is some confusion.

Additionally, I measured the IRE levels for the gray card and made sure that the IRE level was at 50, in the Waveform monitor.

Can you tell me your testing procedure Barry, so I can confirm my tests?
 
Re: Shutter speed "Auto"?  overexposure

First clarification: the testing I did was with the DVX100, not the 100A.  I sincerely doubt there is any sensitivity difference between the cameras.

Second, there was a massive post here that described the testing procedures.  I used a Sekonic L-508C meter, in SPOT meter mode.  You don't want to use the dome because then you're comparing spot against dome.  The DVX has a spot meter in it and measures reflected light, so you have to measure reflected light to get similar readings.

We also used a Minolta spot meter, don't remember the exact model #.

I set the DVX to 1/60, and the spot meter to 1/60, then pointed the DVX at various scenes, then used the spot meter to capture the same general area, and then changed the ASA on the spot meter until the exposures met.  I tested gray cards, white surfaces, and actual objects including walls, skies, bright light, dim light, indoors, outdoors, tungsten and daylight presets, anything and everything.

In every single instance, the spotmeter matched the DVX exposure readings when the spotmeter was set to 640 ASA.

I had a hard time believing it, so I did a second round of testing.  To remove the ND filters from the equation during outside shooting, I set the DVX and the spotmeter to be 1/1000 shutter speed.  The results? 640 ASA.

All in all, I must have shot fifty different subjects, comparing the results of the autoexposure system vs. the spot meter.  Always it came to 640 ASA.

Filmmaker58 had a hard time believing it, so he came over and we tested again.  640 ASA.

Jarred wouldn't believe it, so he tried testing in a different way: he shot a scene using his DVX, then shot the same scene using a digital still camera that's rated at 400ASA.  Set both cameras to the exact same aperture.  The DVX picture was brighter, implying a faster-than-400 ASA.

The spotmeter I use is calibrated in 1/10 of a stop increments.  The DVX has a continously-variable aperture, but the markings occur in half-stop increments.  So many times I would adjust the light level until the DVX's meter would just cross a threshold (i.e., it'd just go from 8.0 to 9.6) and then I'd take a reading that the spot meter would read as 8.0 5 (which means halfway past 8.0).  That should have delivered tenth-of-a-stop accuracy, and the ASA needed to do that was: 640.
 
Re: Shutter speed "Auto"?  overexposure


I believe that you did your test properly. I'm just trying to figure out what's causing the discrepancy.

Also, the DVX's aperture increments are displayed on the LCD as 1/2 stops, but I found that there are 3 miniture 1/9 stops in each of those half stop increment (atleast for my DVX100A). For instance, if you carefully move the aperture dial between 4.0 to 4.8 there is a 4.0 0, 4.0 1/3, and 4.0 2/3 stops.

I think I may know why there is a difference. Can you tell me the gamma setting did you set?

I know for a fact that the Cine curve in DVX100 is different than the Cine curve in the DVX100A. That may have something to do with it. I'm not too sure about the Normal gamma curves between DVX100 and DVX100A though.
 
Re: Shutter speed "Auto"?  overexposure

Oops,

those 1/3s are not 1/3 of a single stop. They are 1/3 of the distance between 4.0 and 4.8, so they should actually be:

4.0 0/6, 4.0 1/6, and 4.0 2/6

Hope that's not confusing...
 
Re: Shutter speed "Auto"?  overexposure

Are you saying that shows up in the viewfinder? Cool... DVX100 doesn't show that, it only shows half-stops. Or are you saying that you can see a physical change in exposure, as if the iris isn't continuously-variable but is calibrated in 1/3-of-a-stop increments (well, I guess it'd be 1/6-of-a-stop)?

As for gamma, I checked it in both Cine and Normal.
 
Re: Shutter speed "Auto"?  overexposure


I wish those 1/6 stops show on the camera, it's really annoying trying to figure out what the exact F-stop. The latter is correct; you notice it on the monitor and on the resulting video output.

So let's say if you have 4.0 on one setting and 4.8 on the other, you could potentially be off by almost a half stop if you don't find out the exact position.

e.g.:

Setting 1 shows f4.0 and is actually f4.0
Setting 2 shows f4.8 but is actually f4.8 5/6 (almost f5.6)

So in that case, if you don't be careful, your tests are not correct.

I'm not saying that you did this, as it seems unlikely if you tried the same test over and over again on different conditions. Most definately the margin of error would reduce as you try the test multiple times -- that is unless you are EXTREMELY unlucky.


But I do think it is Gamma setting that is off-setting the two camcorder. Adam Wilt reviews that the DVX100A's cine's knee is at 100% whereas DVX100's cine goes up to 120% and clips out. The DVX100A additionally has CineD mode and CineV mode, which have knees 105 and 110 respectively. I did some extensive testing, and I'm quite certain this is true.

This is what might be the difference between my tests and yours. Although, I'm not too sure about the Normal gammas...

Hopefully that makes sense.
 
Re: Shutter speed "Auto"?  overexposure

It's one of those days, I'm confusing myself and you guys...

sorry.


What I meant was that for those 1/6 stops was...

You can see a physical change in exposure and not on the
monitor
 
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