Getting a full range of Gain/Exposure with the light trick

[DavidD]

I am experiment with the light aimed at the camera lens trick. Right now, I have -11 -> +11 exposure, with 0 being a little dark, but not overly when the light is removed. I think it looks quite nice, but I want to be sure as I work through it so I can get just the right amount of light going through. Is this what Barry Green was trying to achieve? I have achieved it with a light trick that I put together that I can make quite cheaply and easily. The question is, how do I know if this is exactly the right range for exposure? Thanks

[DavidD]

No takers? Ok, I am going forward with some tests with the light cap I created. Right now, it looks really good. I am worried about this camera because there is the white lines in the middle of the LCD (maybe normal). I am buying a small mini-SD card this week (for under $10.00) and testing it on the camera with the light cap to see how the gain is affected.

[geekd]

I am worried about this camera because there is the white lines in the middle of the LCD (maybe normal).

You mean a grid like a tic-tac-toe board? You can turn that off. Menu -> Display -> Markers

-geekd

[DavidD]

No, it is like thin white lines when the gain is up.

[Abe Ford]

No takers? Ok, I am going forward with some tests with the light cap I created.

I *think* all that matters is achieving a manual exposure where in lowlight you get only one 1.8 f setting displayed, or that you never use the second instance of 1.8. I keep re-reading the various posts on the subject and someday I'll understand it all. Good luck on the LCD problem.

AF

p.s. did you build a lighted lens cap? it would be great to see a picture.

[DavidD]

I did build one, I am just working on getting the right amount of light into the cap. Too much is not good. I will have pics when it is done.

[Lorax74]

Hi,

I ordered my HV20 last night from B&H (thanks to the Where to Buy forum!) and will be receiving my camera tomorrow, it feels like Christmas Eve already .

Could the "white lines" be zebras?

[duketh]

Could the "white lines" be zebras?

no the white lines appear when the gain is up really high.
I've noticed it, it's as if each vertical line of pixels has its own decision on what the brightness/colour/gain/sensitivity (one of them) should be. It is unusable in my opinion but I never try to shoot over f2.0 with the camera.

[DavidD]

Ok, I was thinking about telling my buddy to send his camera to Mack Camera for a repair, but if this is normal, all is well.

With my light cap, I am getting 11+ through -11, which is great, but without a mini-SD card to check the gain, I can't tell what is happening. The picture looks amazing, but I want to be sure. The Mini-SD card should be in before the end of this week for testing.,

[lasssman]

I was thinking of this idea (the light cap). What are you using as a source?

[Abe Ford]

Re: white lines: I would check the Component output when they are present in the viewfinder to see if it will be recorded to tape.

Looking forward to seeing your lenscap deal- right now I'm using my iPod screen, which allows a brightness setting, but it's a bit clumsy for me.

[DavidD]

How do you mean "check the component out"? Do you mean, watch it on a TV?

[Abe Ford]

yes, that's all i'm saying, just in case you haven't tried it already. if your tv doesn't accept copmponent, use composite. i've shot in very low light with gain and didn't notice any lcd lines- but i'll check again.

[lasssman]

I did build one, I am just working on getting the right amount of light into the cap. Too much is not good. I will have pics when it is done.

David, what are you using as a light source?

[Michael Davis]

With my light cap, I am getting 11+ through -11, which is great, but without a mini-SD card to check the gain, I can't tell what is happening.

The miniSD card doesn't give you the gain.

The way the HV20 works is when it detects a specific set of variables, it adjusts it's aperture, gain, and other settings in a very specific, and predictable way. If the set of variables is the same, the settings the HV20 chooses will be the same.

The guy who originally did all this testing figured out that if you completely cover the lens so that the HV20 only sees black, then lock the exposure, and adjust the exposure to -11, you will have a wide open iris, no gain, and a 1/48th shutter speed. Every time you do this you'll get the same results. Personally these are the settings I want almost EVERY shot, so even when this results in too bright of an image, I just use neutral density to stop out some light, rather than change any of those three settings.

It gets tricky when you'd like to close your iris for more depth of field, or change your shutter speed (possibly for artistic reasons).

When you do the trick where you completely cover the lens, you only get one useable exposure value: -11. However, if you shine a moderate amount of light into the lens, you can get values from -11 to 6 or so that have no gain. The problem is, every light source you use is different. But if you use the same light source every time, and you learn what settings are usable with that light source, you can get repeatable results. When people refer to the "cell phone trick," they're using their cell phone's screen to fill the lens. Every time they use the same light from the same screen of the same cell phone, the exposure values the HV20 chooses will be the same.

So if you built a light cap, there's no way anyone but you can record the exposure values you get from the HV20 when using it (unless you mail it to someone to test for you :P).

The way to do it is to shine the light from the light cap into your camera, lock the exposure, then see what each setting on the exposure slider results in. There is a program that some German kid (or somewhere in Europe I believe) made that when your HV20 is plugged into your computer via Firewire, it will tell you what your current gain is. if you have a PAL camera, it will also tell you your iris and shutter speed, but it reports incorrect values for an NTSC camera (but the gain is still correct.)

So since no one can tell you what settings your light cap generates, you're going to need this program (I'm sure someone else who posts on this forum can link you, I've just moved and I'm on a laptop stealing wireless internet from a neighbor, I have the program on my desktop) and you'll need a miniSD card.

Keep in mind the only reason to do any of this is to avoid gain. If you can live with electronic gain, don't bother, just move the exposure slider until your shot looks good to you and record.

[DavidD]

I have managed to get 1.8 all the way to +11 on the exposure. I assume this is what most people are looking for... The light coming in is just adequate for this to work.
Now, making this with an on/off switch is the next step!

[Michael Davis]

Um...

Keep in mind the only reason to do any of this is to avoid gain.

That is what most people are looking for. At +11 you might have a bunch of digital gain added. Without actually checking you'll never know, and then building a light cap was a waste of time.

edit---
From re-reading this thread, I think you might be mistaking your aperture (how open your iris is, measured in f-stops) with digital gain (which is the computer in the camera trying to brighten the image digitally, which results in digital noise in the image). Having your camera's aperture set to f1.8 is not the same as having no digital gain.

[DavidD]

Ok,
Made a lens cap that works everytime. I get the same readings as Barry Green
http://www.dvxuser.com/jason/hv20/
When the camera is first turned on, it is 0 1/48 3.7 0dB (with the 1/2 push on the photo button), I zoom in a bit and then back out to full, check the 1/2 push button again, I am at 3.4, zoom in and out fully again, 2.8 - lock the exposure and now it works perfect (only takes about 20 seconds in all to get to 2.8). I have done this 10 times in a row, each with the exact same result. It is nice to put on the lens cap and not worry about holding a cell phone in front to achieve the same thing.

[lasssman]

DavidD - I have asked this twice so far, and you are not responding. What are you using for a light source?

I'm running out of time - if I am to build something for a trip I am about to take, I now only have a week left.

I'm disappointed that you seem to think this is a great secret - I can understand that you have testing to do, and want credit for the idea. That's not a problem for me - but right now I really would like to know what you are using. Who knows - I might even be able to contribute.

[Chuck]

I agree... what's the light source? Pictures?

And, how are you checking your gain?

[DavidD]

Lassman, I didn't want to promote something until it worked - I am sure you can understand that. If it didn't work, I would get flamed about how it 'didn't work', so that is why I waited.

I am using a LED light. I attached a 3V circular battery to it. To get the diffusion, I use a range of materials to get it so that it is the correct brightness. Wax paper is one of them of the diffusers among others.

As for gain, I am using the same principles as Barry Green - light into the lens at 2.8, lock the exposure. I then check with my HC1 and see that there is 0dB of gain all the way to +6.

[Ian-T]

David, it's good that you are doing this. I think lassman, including myself, is eager to see your progress. If you had pictures available maybe some other wise individual here could give you some pointers to help you along the way. That's usually how I see other DIY projects go...but...I understand...that is totally up to you.

[DavidD]

I am excited about this as well. I borrowed my friends HV20 camera, AND was so impressed I bought one myself. Now, I am testing out the light cap. I was thinking about putting an on/off switch, but it starts to get complicated with the wiring, so I am not sure if I want to go that route just yet.

[nzo]

Likewise I'm looking forward to seeing/hearing more about your experiments lasssman. No pressure...just quietly waiting in the wings

[Chuck]

Has anyone ever tried one of the tap lights?

http://www.amazon.com/American-Tack-.../dp/B00004XS9T

I have one around somewhere, I will have to dig it out. It is a little bigger than I'd like, but would definately fit in a camera bag for quick access. If they made one half the size it might be perfect.