HV20 gain

With lens capped, in CINE exposure mode, and 24P, I stepped through the range of exposure options. The exposure dial goes from +3 to -11.

+3: 1/8 f/1.8 10.5dB?
+2: 1/15 f/1.8 10.5dB?
+1: 1/15 f/1.8 9dB
+0: 1/24 f/1.8 9dB
-1: 1/24 f/1.8 7.5dB
-2: 1/24 f/1.8 6dB
-3: 1/24 f/1.8 4.5dB
-4: 1/24 f/1.8 3dB
-5: 1/24 f/1.8 1.5dB
-6: 1/24 f/1.8 0dB
-7: 1/24 f/1.8 0dB
-8: 1/30 f/1.8 0dB
-9: 1/30 f/1.8 0dB
-10: 1/30 f/1.8 0dB
-11: 1/48 f/1.8 0dB


So -- there's a way that you can force 1/48 and 0dB of gain -- set the HV20 in CINE mode, cap the lens and lock the exposure, then force the exposure dial all the way down to -11. Problem is, you've now taken away the iris as a means of setting exposure, so how do you account for changing light conditions? You could do it with an arsenal of ND filters I guess...
 
In exterior conditions, pointed at a moderate sky (not blazing sunlight, but still a moderately bright sky) and 24P/CINE mode, it defaulted to F/5.6 at 1/48. I then locked exposure and ran through the gamut.

+11: 1/48 f/4.8 0dB
+10: 1/48 f/4.8 0dB
+9: 1/48 f/5.6 0dB
+8: 1/48 f/5.6 0dB
+7: 1/48 f/5.6 0dB
+6: 1/48 f/5.6 0dB
+5: 1/48 f/5.6 0dB
+4: 1/48 f/5.6 0dB
+3: 1/48 f/5.6 0dB
+2: 1/48 f/5.6 0dB
+1: 1/48 f/5.6 0dB
+0: 1/48 f/5.6 0dB
-1: 1/48 f/5.6 0dB
-2: 1/48 f/5.6 0dB
-3: 1/48 f/6.7 0dB
-4: 1/48 f/6.7 0dB
-5: 1/48 f/8.0 0dB
-6: 1/60 f/8.0 0dB
-7: 1/75 f/8.0 0dB
-8: 1/90 f/8.0 0dB
-9: 1/100 f/8.0 0dB
-10: 1/120 f/8.0 0dB
-11: 1/150 f/8.0 0dB

I have no explanation fo rthis one, I have no idea what it was doing between +9 to -1, there's no discernable difference in the exposure data, but there's a massive difference in the recorded image. The aperture and shutter and gain didn't appear to change at all, but the image definitely got much brighter.

My question is -- is there some sort of "adjustable ISO" system that the camera goes through? Like gain, but not classified as gain? A "stealth" gain? I stared in the iris while walking it through its range of - to +, and couldn't see any evidence of any neutral density filters moving into place or anything (nor could I see how that would even be practical!) So what is it doing? I suspect it's some sort of CMOS ISO adjustment, which is in effect "gain", but not classified according to the data code as "gain".

I don't know what that means though, as far as quality of image. From experimenting with it, it seems like the CINE system does prefer 1/48 when it can get it, but you can definitely get shutter speeds way out of range when using CINE mode (anywhere from 1/150th all the way to 1/8th). If you want to know for sure you're getting 1/48th, the only way to assure yourself of that is to use the Shutter Priority mode.
 
When using Shutter Priority (Tv) mode: starting with the lens capped is useless, because it starts with 27dB of gain. So you have 1/48th, but even if you push the exposure all the way down to -11 you'll still have 12dB of gain...
 
Wow, thanks Barry! Even though I won't own a HV20 (Maybe later, as a tapedeck for the ordered XHA1), this was like a peek into a masterclass.

:)
 
Barry, you're the man.

Does the camera at least tell you what it is doing so far as aperture, shutter speed, and gain are concerned? In other words, were those numbers easy to find for any particular setup? This would at least prevent you from being surprized at the result of any image.

If there was only a way to lock any or all of the variables at will. You could lock gain at 0db, shutter at 1/48, and then adjust the iris for exposure. That might be asking too much from a $1,000 camera, but my thinking is this: they already have the control system in place for the camera to adjust all of those three variables--why not just open that control to the user?

But I guess you can't always get what you want.
 
Does the camera at least tell you what it is doing so far as aperture, shutter speed, and gain are concerned?
Click to expand...
No, not at all. It gives you none of that info if you're using any of the programs. The only feedback you can get is if you use Aperture Priority (which will tell you the aperture, but nothing else) or Shutter Priority (which will tell you the shutter, but nothing else).

In other words, were those numbers easy to find for any particular setup?
Click to expand...
No, it was a royal pain in the butt. You can find out shutter speed and aperture after the fact, by turning on the data code and playing your footage back, but it won't show you gain at all. The *only* way to find out what gain you were at is to take the tape out of the HV20 and play it in another HDV camcorder that DOES display the gain in the data code (i.e., it's recording the gain info to the tape, but its display system won't show you that data!) I dug up a Sony HDV camcorder, turned on the data code, and then played the HV20 tape in it to find out what the gain was. So I had to spend a couple of hours running the HV20 through every possible configuration, narrating it the whole way, and then playing it back on the HV20 to find out what the shutter speed was (because the Sony HDV camcorder doesn't recognize and won't show 1/48 or 1/24; it lies to you and says it's 1/30 or 1/15!) So playing on the HV20 is the only way to figure out what the real shutter speed was, but it's useless for figuring out the gain. So I'd make notes on what all the shutter speeds were, then have to rewind the tape and play it on the Sony to get it to tell me what all the corresponding gain values were.

But you cannot know what the parameters are while you're shooting. If this were a $2500 camcorder I'd call that a fatal flaw. But for a $925 camcorder, I'm still grinning that I was able to figure it out, and that it's controllable enough that if you jump through enough hoops you can sort of get what you want from it. It's like overclocking a CPU, or putting a hopped-up exhaust system on your Honda Civic; it's totally a game of beat-the-camcorder... :thumbsup:

If there was only a way to lock any or all of the variables at will. You could lock gain at 0db, shutter at 1/48, and then adjust the iris for exposure
Click to expand...
That's what pro/prosumer cameras are for. The HV20 isn't anywhere near that same class, it's a little pocket-cam. Can make some pretty pictures, but in no way is this little cam comparable to an XHA1 or DVX as far as controls and feedback.

I'm thinking that if you wanted to actually use this in any sort of controlled circumstance, you might have to lock it at 1/48 & f/2.8, and then just use a stack of ND filters to control exposure. I'm almost wondering if one of those variable-ND filters might be the way to go... http://www.singh-ray.com/varind.html (of course, that filter costs half as much as an HV20, so that's not a good solution for those who'd be buying an HV20!)
 
Last edited:
Y'know, the one way I've been able to find a common baseline/ground for the HV20 is to completely cap the lens, so you know exactly what the HV20's going to expose at in any circumstance, right? Well, I'm thinking... the ultimate HV20 accessory would be some sort of light source that you could clamp onto the front of the lens, that emits a certain # of lumens of light (whatever the appropriate # is) in order to cause the HV20 to default to 1/48 & f/1.8 at 0dB. So you'd put on this thing to the front of the lens and tell the HV20 to expose, and it'd measure the incoming light and set for 1/48 & f/1.8, right? Then you could lock the exposure there, and have full use of the EXP range and it should only be affecting the iris at that point.

I wonder if I could figure out some graphic to display on a laptop, or if there's a cell phone LED that would emit enough light, or... I dunno, just thinkin'... for example, I brought up the B&H Photo site on my Dell 2405, and stuck the HV20 to where it was butted up against the screen, so the whole sensor is filled with the projected white light. Then I locked exposure using Tv(1/48). And I found I could get nearly the full range of exposure, from f/1.8 down to f/5.6 (but deep into f/5.6, I can't explain that, -2 to -11 all show f/5.6 somehow) and all of it at 0dB of gain. That's practically useful. Only thing is, you'd have to do this every time you moved into camera mode, every time you turned the camera on, etc. So you'd need a portable system (which is why I'm wondering if you could display something on your cell phone LCD that fills the screen and provides enough light to move the HV20 into middle-ground exposure, thus giving you the full range...)
 
Last edited:
Okay, so here's the new test -- I used my Nokia N93 phone's web browser to bring up Yahoo (a mostly-white screen) and used that as a "lens cap" on the Canon. Put it in CINE mode and locked exposure, then run through the gamut.
+11: f/1.8 3dB 1/24
+10: 1.8 0dB 1/24
+9: 1.8 0dB 1/24
+8: 1.8 0dB 1/30
+7: 1.8 0dB 1/30
+6: 1.8 0dB 1/30
+5: 1.8 0dB 1/48
+4: 2.0 0dB 1/48
+3: 2.2 0dB 1/48
+2: 2.4 0dB 1/48
+1: 2.6 0dB 1/48
0: f/2.8 0dB 1/48
-1: f/3.1 0dB 1/48
-2: 3.4 0dB 1/48
-3: 3.7 0dB 1/48
-4: 4.0 0dB 1/48
-5: 4.4 0dB 1/48
-6: 4.8 0dB 1/48
-7: 5.2 0dB 1/48
-8: 5.6 0dB 1/48
-9: 5.6 0dB 1/48
-10: 5.6 0dB 1/48
-11: 5.6 0dB 1/48

This might actually be workable. It's a field solution, it forces it to a set level, and you have usable range from -11 all the way up to +5. That's not bad. I'll have to try it in the field and see how practical it is outdoors... :thumbsup:
 
Last edited:
Sounds like you need a lens cap with led's inside of it. A watch battery (hopefuly) and a button on the lens cap. It's a lens cap. But, press the button and it's your exposure cap. Sounds like a vidled thing...
 
Tried it with my phone, loading up a JPG of pure white. It gave slightly more usable range, anything from -11 up to +6. I'm almost happy with that, but it'd be nice if I could get some additional range...
 
Barry,

it seems that in Photo mode, you can view the shutter speed value and the apature value and the manual exposure value - all at the same time... that's what it looks like in the manual on page 17. can you use this?
 
if it works, then you could just take a photo of your live stream, then check what all your values where in photo mode...

and you get a histogram!
 
I did some experiments a few days ago and came up with this:

I was a bit concerned about manual control after trying out the HV20 tonight. My concerns are somewhat allayed after doing some experimentation. If someone comes out with a camera with the HV20 imagery, and the GS400 controls...look out. After getting used to that "consumer" cam's manual controls, the HV20 is a bit of a disappointment. Whoever puts the HV20's 24p imagery in a Panasonic GS400-like chassis will have a runaway hit product with the prosumer crowd.

In any case, here's part 1 of a mulit-part post on using the HV20 as an adapter cam. I placed the HV20 in shutter priority mode (TV), pressed the joystick to bring up EXP control and toggled it on. I went from -11 to +11 and then observed the aperture blades directly looking through the lens both with an LED headlamp, and then at an angle with overhead light. It is very apparent that the adjusment gradient will vary depending on the auto exposure level the camera has dialed in when you engage exposure control.

Based on my initial observations, here is what I would suggest for adapter use shooting 24P.

1. Set zebras at 70%
2. Set camera to 24P mode
3. Switch to TV mode, and set at 1/48s
4. Frame a shot so about 50% of the frame is displaying zebras. This is so the cam is neither fully gained up, or fully stopped down. It's just an approx. baseline.
5. Press joystick and toggle EXP on.
6. At this point here is a rough guide to what the EXP settings correspond to.

-11 = Aperture 80% closed, ND2 fully engaged.
-6 = Aperture 80% closed, ND2 full disengaged, ND1 visible.
0 = Apeture fully closed, ND1 disengaged completely.
+5 = Aperture 50% open.
+11 = Aperture 100% open.

Max sharpnes for this lens is likley somewhere around +9 on this scale. If you engage EXP with TV on and shutter at 1/48s but the cam pointed zoomed in on a light, you'll see 100% aperture closed, and I'd guess 100% ND filter engagement too.

If you want at least a vertical flip, here are some pics of how to do it.
 
Jason Ramsey said:
Sounds like you need a lens cap with led's inside of it. A watch battery (hopefuly) and a button on the lens cap. It's a lens cap. But, press the button and it's your exposure cap. Sounds like a vidled thing...
Click to expand...

Yes, I could make something like that, no problem.
Barry, how much luminocity spread can this thing have? Also, you mentioned that the Sony is mistakenly reporting the shutter speed; how do you know it is the Sony who is reporting this wrong, and not the Canon? Just curious if this was actually established that the Canon IS true 1/48 second.
 
Barry, you are the man for sure. Thanks for being so persistent about this. You seem to be working out a good way to get the most out of it. I haven't got my hands on an HV20 yet but my old Sony handycam apparently adds gain if you set the exposure to max. I looked into the lens and saw that the iris was wide open at max exposure and it didn't start to close until I stepped down 7 steps, so the last 6 steps are all just adding gain.

When you were talking about variable ND-filters to control exposure I couldn't help to think that maybe a 35mm adapter would be another way to do this. You'd have a manual iris ring on the lens on the adapter. But how should this be done? I recon the iris on the camera should be wide open and shutter speed should be locked and then you control the exposure with the lens on the adapter. Is there a way to open up the iris to fully opened without introducing gain on the HV20? Based on my tests with my old Sony I don't think you will get a bright picture enough with a 35mm adapter if you just open up the iris as much as you can and then don't go any further by adding gain.
 
Last edited:
vidled said:
Also, you mentioned that the Sony is mistakenly reporting the shutter speed; how do you know it is the Sony who is reporting this wrong, and not the Canon?
Click to expand...
The Sony's an old FX1, almost three years old now, and it came out before there was such a thing as 1/48 and 1/24. So it doesn't have the capability to report those numbers.
Just curious if this was actually established that the Canon IS true 1/48 second.
Click to expand...
That's one of the few things I can actually verify; according to the Canon's manual, yes it is 1/48. And you can manually select 1/48 or 1/24 in the Tv mode. So I am of the opinion that the Canon's telling the truth, it actually is 1/48, and that the Sony's translation/lookup table just doesn't have an entry for 1/48 so it reports the closest value it can find in its list (which would be 1/30 apparently).
 
Dennis Wood said:
-11 = Aperture 80% closed, ND2 fully engaged.
-6 = Aperture 80% closed, ND2 full disengaged, ND1 visible.
Click to expand...

See, this is what puzzles me -- I couldn't see any evidence of there being a physical ND filter in there. I did a similar test, got under a very bright light and used a flashlight, and stepped through the whole raft of options, and I can see the aperture closing down fine but I never saw any evidence of any ND filters sliding into place... and how would it be able to execute a physical filter sliding into place in the middle of a shot? I don't get it. I mean, I'd like to understand this better, as the presence of some manner of ND filters would help explain what the heck is going on at the lower end of the scale, but I couldn't find any evidence of 'em. Did I just miss it somehow? Maybe I didn't have it stopping down far enough to engage 'em?

Also, as for variable ND filters -- the Singh Ray variable ND is $400. Er, that's a tad expensive for a $925 camcorder. But apparently the Singh Ray Vari-ND is merely a circular polarizer with a linear polarizer in front of it. So you could probably grab a circ-pol and a linear-pol off ebay cheaply, stick 'em together, and come up with a similar solution.
 
Norbert said:
When you were talking about variable ND-filters to control exposure I couldn't help to think that maybe a 35mm adapter would be another way to do this. You'd have a manual iris ring on the lens on the adapter.
Click to expand...
Yes, you could do this. But you shouldn't, because 35mm adapters usually only perform well at about f4 and above; stopping down below f/4 usually involves making the grain of the ground glass apparent, and the more you stop down the more visible the grain gets. You should be using the camera's own iris and ND filters to control exposure.
 
Thanks for all the info Barry, very much appreciated.

Have you done any tests of what the aperture would be at full telephoto?
 
zoom X - widest aperture

0 - 1.8
1 - 1.92
2 - 2.04
3 - 2.16
4 - 2.28
5 - 2.4
6 - 2.52
7 - 2.64
8 - 2.76
9 - 2.88
10 - 3
 
You must log in or register to reply here.
Back
Top