HV20 gain

Jay Stebbins said:
I am in the middle of John Jackman's "lighting for digital video and television". It has been a very good read so far.

* Warning---- I am 3/4 through the book, there might be something on the last page that shoots this all to hell......
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Thanks Jay,

Yes that book was AWESOME. I read it in one read (whew) but need to go back again and take some notes now. Looking forward to some greats shots with the HV20 and Brevis. Seems like a match made in (affordable) heaven.

Thanks!

Rob Robinson
 
Robert Robinson said:
This seems like a comfortable solution considering that there is a constant shutter speed and ZERO gain. The iris on the camera is not that important (as long as its greater than 1.8) since the aperture on the mounted lens on the adapter is what is really being used to dial in the exposure (and DOF).
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If you don't have a miniSD card you could also look at the iris through the lens of the HV20. When it doesn't open up anymore it starts adding gain instead (if your shutterspeed is locked). I think Barry mentioned earlier in this thread that it would not be a good idea to use the iris on the 35mm lens if you want to step down below F4.0 to get a proper exposure. Apparently that's where you start seeing the grain on the ground glass of the adapter.
 
Norbert said:
If you don't have a miniSD card you could also look at the iris through the lens of the HV20. When it doesn't open up anymore it starts adding gain instead (if your shutterspeed is locked). I think Barry mentioned earlier in this thread that it would not be a good idea to use the iris on the 35mm lens if you want to step down below F4.0 to get a proper exposure. Apparently that's where you start seeing the grain on the ground glass of the adapter.
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Good point (about just looking at the iris) except that with the 35mm adapter connected its more difficult to do (would have to remove it first). Taking the PHOTO is also not all that convenient but hey its all about the least amount of painful work around I guess. Also, from my experience with the Brevis (and certain faster lenses) you can actually go past F4.0 and still be fine (as far as no visible grain).
 
Actually, taking a photo while shooting is very easy. You just hold down the photo button next to the zoom toggle while you are in video mode. The aperture will show up briefly in the lower right corner. If you want to see the histogram, then you need to switch over to view the card.

It is better than nothing. I just wish we could turn off the gain like the Everio....

Jay
 
Jay Stebbins said:
Actually, taking a photo while shooting is very easy. You just hold down the photo button next to the zoom toggle while you are in video mode. The aperture will show up briefly in the lower right corner. If you want to see the histogram, then you need to switch over to view the card.

Jay
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Jay, I just tried that - I get a little red box in the lower left that says [Off] instead. Is there a setting I need to turn on?


EDIT: Just found it - "Still Image Set" - Cool! That makes it sooooo much easier!

Thanks!

Rob Robinson
 
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Interesting... When using PHOTO in video mode (thanks Jay!) you see the aperture (or is it? - read on) and the shutter speed (if you press the PHOTO button down halfway). What is interesting is that the lowest reading is F2.2 (lens cap on) and then it increments by .2 as you add more light (i.e. 2.2, 2.4, 2.6, 2.8 etc...). This must be the addition of gain between stops I would imagine? (1/3 increments) So, in order for the ZERO gain trick to work we'll need to stay clear of the bottom (2.2) and look for something like 2.4 I would think? Although, I caught it reading 3.6 which the is the next few stops down (3.4) plus presumably some gain!? Oh no! So is the answer to make sure that the reading is EXACTLY the stop intervals? (1.8, 2.0, 2.4, 2.8, 3.4, 4.0, 4.8, 5.6, 6.7, 8.0 as per the manual page 47). The assumption being is that the display is yielding actual EXPOSURE readouts (not just the iris ). So as long as the figure is one of the iris settings (with no added gain increments) then we're OK? I think this PHOTO trick may be giving us just the info we need!

EDIT: Now that I think about it, 2.2 (with lens cap on) must be almost wide open iris (2.0) plus an increment of gain (2.0 + .2 = 2.2). Makes sense now. So 2.2 is bad, very bad... 2.4 on the other hand sounds like ZERO gain to me!

EDIT: FOLKS WE MAY HAVE IT! I was able to lock in the shutter at 1/48 and the EXPOSURE (iris + ZERO gain) at 2.4 (can't get to less than 2.4 it seems) and then I had total exposure control with the brevis 35mm adapter. SWEET!!!!

EDIT: For those without a 35mm adapter (not to leave anyone out here), you can still adjust the EXP bar and then see what the actual EXPOSURE is with the PHOTO method (above), then lock it in (by leeaving the EXP bar displayed). Again, in order to have ZERO gain, my conjecture is that the readout needs to be an interval of 2.4, 2.8, 3.4, etc.. (The list of available apertues on page 47)

EDIT: I have the term "Gain" confused with ND filters in this post - duh!

Thanks!

Rob Robinson
 
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No, 2.2 and 2.4 won't represent gain at all. 2.4 is a 1/2-stop marking between 2.0 and 2.8, so 2.2 and 2.6 are 1/4-stop settings. Either way they should be at zero gain.

You'll only have gain creeping in if you open up wider than the maximum; even so the iris should still show maximum. The increments you're seeing are not gain. The HV20 won't tell you what gain it's at, at all, near as I can tell.
 
Barry_Green said:
No, 2.2 and 2.4 won't represent gain at all. 2.4 is a 1/2-stop marking between 2.0 and 2.8, so 2.2 and 2.6 are 1/4-stop settings. Either way they should be at zero gain.

You'll only have gain creeping in if you open up wider than the maximum; even so the iris should still show maximum. The increments you're seeing are not gain. The HV20 won't tell you what gain it's at, at all, near as I can tell.
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Barry (in my most humbled voice),

Aha! I may have it backwards (told you I was a noobe). I may have gain and ND filters reversed in my thinking. So to go from 2.0 to 2.2 that is not GAIN being added, but likely an ND filter? Gain is added when going the other direction (from 3.8 to 3.6 lets say). Ok, to restate what the GOAL is then: We want ZERO gain and NO ND filters perhaps? Does my original conjecture still stand though? That as long as the EXPOSURE reading (via PHOTO) is an interval of the actual aperture values then we can be assured that no gain or filters have been added? I mean why would they is the iris has taken care of it first?

Thanks!

Rob Robinson
 
No, 2.0 to 2.2 to 2.4 to 2.8 ... all the way down to 8.0 and 9.5 and 11, etc, are all indications that the iris is getting smaller.

The goal is zero gain, with a 1/48 shutter; whether there are filters present or not. And that's the one thing the HV20 doesn't tell you, is the amount of gain it's adding. However, presumably if it's smaller than maximum wide open (and that number changes depending on what zoom position you're at!) there should be no gain.

So as long as it's not wide open, there's probably no gain being added.
 
Barry_Green said:
So as long as it's not wide open, there's probably no gain being added.
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I got ya now. So, since 2.4 is not wide-open then like you say "probably no gain being added". Works for me!

Thanks!

Rob Robinson
 
Hey Robert,

Wide open is f/1.8... At 1.8 the iris is wide open to let in the light, just like your eyes. If the camera had started to show f/stops like 1.1 or .7 then your theory on gain compensated aperture readings would have been right. The more wide the aperture the more shallow the depth of field will be as well. When the hv-20 can't open the aperture any further to let in more light, it starts adding gain. It is like using a faster film (higher ISO) in a camera. The higher the ISO or gain, the more grain is introduced to your picture.

When you stop down a lens, make the iris smaller, let in less light, like your eye does when you step outside, the f/stop number goes higher (f/11-f/20?). When the aperture gets as small as possible the HV-20 slides Neutral Density filters in place to keep the picture from becoming over exposed. The more you stop down a camera the wider the depth of field becomes.

The various scene settings will change when gain is added, ND filters are engaged, shutter speed limited. Slowly through people experimenting and sharing, maybe we can figure out what this camera is doing.


I hope this helps put a little more of this in perspective.

Good luck,
Jay
 
It's 1.8 at wide angle, but when you zoom in then it becomes more like 2.8 or so. (I don't have it in front of me so can't verify right away). But the point is, it's not a constant 1.8; it depends on your zoom setting.
 
Jay Stebbins said:
Hey Robert,

I hope this helps put a little more of this in perspective.

Jay
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Jay,

Thanks, that does help clear some things up for me. Especially the part about the ND filters not being added until the iris is the smallest (didnt know that). On my post I really had gain and filter backwards (long day). I do know the difference, but its just hard to keep them straight when referring to the exposure settings, etc...

Barry,

Your point about the zoom setting makes total sense to me know. Thats why I can't see 1.8 with the lens cap on (as I would have expected). I'll have to check what zoom I had it on when I read 2.2 as the bottom in my example.

So, my next question is that what are those .2 increments all about? If they are not gain (since we're in the middle of the iris range) and they are not ND filters then what are they? Is it possible for the HV20 to do 1/2 and 1/4 stops (physically?) So, unlike a real lens you can have partial stop movements?

If that's the case then perhaps the "new" plan of attack would be to put the lens cap on (to get the iris opened up as much as possible) then depending on your zoom settings you would see an APERTURE readout (not compensated exposure as I originally thought) by using PHOTO and the EXP bar readout for +0. Then increase the EXP bar until you see it add at LEAST one .2 increment (i.e. from 2.2 to 2.4). Then you'd know that you are now free from any GAIN (and now I've learned free of any ND filters as well). Then either leave it there (I think I will) or perhaps then move it back one EXP "notch" to have the iris as wide-open as possible with the hope that you're still free from gain (two notches and you'd be asking for trouble for sure)?

Wow, this stuff is tricky! Thanks to you both for having patience with me as we figure this out. I very much want this "little cam that could" to work out!

Thanks!

Rob Robinson
 
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Ok, tried a few things...

First, my zoom setting is about 1/3 zoomed in (in order to frame the GC in the Brevis 35mm adapter perfectly). As Barry points out that affects what the lowest iris setting can be (the range is in fact from 1.8 (wide) to 2.8(full zoom) ).

After knowing my "bottom" was 2.2 (for my given zoom), I then looked at what EXP adjustments I could make. Well, with the lens cap on you can't increase (only decrease from +0 to -11). Makes sense since one would expect the cam to try to add MAX gain with total darkness (lens cap on). So I figured that using the lens cap alone won't do the trick (since I can't get the aperture to move off from 2.2 I can't reliable say for sure that I've removed all the gain it was adding).

So, instead I tried this. I took the lens cap off, the then pointed the cam so that I registered anything greater than my bottom of 2.2 (although staying as close to 2.2 as possible). As an example, I read F3.4 on the cam (again using PHOTO - love that BTW), then set the EXP bar to +0 to "lock it in". Then with each successive movement of the EXP bar (increasing) the APERTURE reading went from 3.4 to 3.2, 2.8, 2.6, 2.4, and finally back to 2.2 (which was +5 on the EXP bar). Then for the final test, I kept going (to +6 through +11) and as expected the APERTURE didnt budge (stayed at 2.2), BUT you could see GAIN being adding to the picture (again as expected when the iris is "wide-open"). I then put the EXP bar back to +5 (which is 2.2) and I think I am fairly confident now that a) I have the iris as wide open as possible (given the zoom setting) and that I have ZERO gain added by the camera!

EDIT: So the take home here is that you first need to "find your bottom" that is dependent on your zoom setting by using a lens cap (total darkness).

Are we there yet?

Thanks!

Rob Robinson
 
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Robert, all that makes perfect sense to me. Stupid question maybe, but do you need a miniSD card in the camera to use the PHOTO button trick? I can't get it to work in camera mode and I'm starting to think it's because I don't have a card.
 
Norbert said:
Robert, all that makes perfect sense to me. Stupid question maybe, but do you need a miniSD card in the camera to use the PHOTO button trick? I can't get it to work in camera mode and I'm starting to think it's because I don't have a card.
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Yes, you do need a card (although by pressing the PHOTO button down only half way you never really take a picture - and thus fill up the card with junk). You also need to set "Still I Rec." to ON in the menu.
 
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I took some inside and outside shots today and tried out the new technique. I'm happy to say that it is a very workable solution (for me at least). One other thing that helped was to turn OFF the BEEP so that when pressing the PHOTO button halfway (which you end up doing a lot to verify the aperture) it doesn't get annoying. I can now within a few seconds of framing the shot press EXP, dial in my "bottom" setting of 2.2 (based on the zoom setting), and then lock it it in for the duration of the shot knowing that BOTH shutter speed and aperture are now FIXED and that there is no GAIN being added to the shot.

Now, I'm experimenting with good combinations of using the lens aperture on the Brevis 35mm adapter and HV20 aperture as both in combination equals the ultimate exposure. On the one extreme I'd like to only use the 35mm adapter (and thereby maximize my DOF) but at some point the grain from the GC (from the adapter) interferes so I may need to increase the aperture on the HV20 (which I can now do reliably using the EXP bar and PHOTO buttons). Bummer of course is that whatever settings I used on the 35 adapter won't be recorded on the tape (for playback reference). So, my latest thought is to FIRST decide what DOF I'm interested in, set the 35 adapter aperture accordingly and then set the aperture on the HV20 in order to set the final exposure (checking zebras, etc...) What's handy is that when you turn EXP off the HV20 tries to find "optimal" exposure for you anyway and its a good place to start from when then going back and manually adjusting the final desired aperture setting .

EDIT: For reference the complete sequence:

1) TV mode (shutter priority) - Set shutter to desired speed (1/48 for 24p)
2) Set "Still Image Rec" to ON - in order use the PHOTO button in video mode (you'll also need a mini-sd card in the cam)
3) Frame the shot (set zoom)
4) Put lens cap on
5) Press the PHOTO button down halfway - this will display current aperture and shutter
6) Note what the aperture setting is. It will be between 1.8 and 2.8 depending on the amount of zoom. Lets call this the "bottom" iris setting.
7) Take lens cap back off and re-frame shot
8) Select EXP bar (with joystick)
9) Press PHOTO button down halfway and note aperture
10) While moving EXP bar (increase or decrease) also press PHOTO button halfway to select the desired aperture
11) Note that once the aperture is at the "bottom" iris setting as noted in step 6 then any more movements of the EXP bar will introduce gain (so dont go past this if you want ZERO gain)
12) Press joystick again to leave just the EXP bar displayed so that the exposure is now FIXED.
13) Record footage! - knowing that shutter, aperture, and gain are all under your control!
 
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